Ecu Pinout | 4s-fe

The story of the Toyota 4S-FE ECU is one of survival and precision. As part of Toyota’s legendary "S" engine family, the 4S-FE was the refined, 1.8-liter workhorse often found in the JDM Toyota Corona (ST190) Toyota Chaser

. Its ECU is the "brain" that manages fuel economy and smooth idling, but after decades on the road, these units are known for common electronic aging issues. The Pinout: Decoding the Brain

Understanding the pinout is the "key" to diagnosing a car that won't start or has a rough idle. While specific configurations can vary slightly by year (early 90s vs. late 90s), a typical 4S-FE ECU uses a standard Toyota multi-plug arrangement (often 26-pin and 16-pin connectors). Common Terminal Purpose in the Story Switched Power (+12V) The "Heartbeat"—without this, the ECU never wakes up. Constant Battery Power

The "Memory"—keeps your fuel trim and diagnostic codes saved. Computer Grounds

The "Anchor"—corroded grounds are the #1 cause of "ghost" sensor errors. Ignition Trigger/Feedback

The "Spark"—IGT tells the coil to fire; IGF tells the ECU the spark actually happened. Fuel Injector Pulses

The "Pulse"—these pins ground the injectors in pairs to deliver fuel. Water & Air Temp Signals

The "Senses"—essential for the ECU to know if it's a cold morning or a hot highway run. Pressure Intake Manifold

The "Breath"—the MAP sensor signal used to calculate engine load. The "Mid-Life Crisis": Capacitor Failure

The most common "plot twist" for a 4S-FE owner involves the internal electrolytic capacitors

. Over 20–30 years, these small components can leak acid onto the circuit board, eating through the copper traces.

Intermittent stalling, refusal to start when hot, or a "Check Engine" light that never illuminates.

Enthusiasts often perform a "re-cap," replacing the old capacitors with modern, high-heat versions to bring the "brain" back to life. The DIY Swap: Modification & Diagnostics

If you are performing an engine swap or troubleshooting, use the

terminals in the diagnostic "Check Connector." By jumping these pins with a paperclip, you can force the ECU to "blink" its diagnostic codes through the dashboard light, revealing hidden engine secrets without needing a scanner.

Always verify your specific ECU part number (e.g., 89661-xxxxx) before soldering, as JDM and export models sometimes swap pin locations for emissions equipment. You can find detailed technical guides and user discussions on forums like ToyotaNation wiring diagram

for a particular Toyota model like the Corona or the Carina? 4E-FE ECU Pinout and Wiring Details | PDF - Scribd

Electrical Load Signal System. Taillight Relay. AC2. Unknown. 12V To Aircon Computer. TE2. White-Blue. Check Connector. TE1. Gray. 4E-FE ECU Pinout and Wiring Guide | PDF | Throttle - Scribd

The Toyota 4S-FE engine is a 1.8L variant of the S-series family, commonly found in JDM (Japanese Domestic Market) vehicles like the Corona (ST190) and Carina. Because it was largely a Japanese market engine, finding English-language pinouts can be tricky, but it shares significant architecture with the more common 3S-FE. 💡 Key ECU Pinout Highlights

For the 4S-FE (specifically the ST190 generation), the ECU typically uses a three-plug configuration (26-pin, 16-pin, and 22-pin). Power & Ground: B+ / +B1: Switched power from the EFI relay. BATT: Constant 12V for memory. E01 / E02 / E1: Main computer and power grounds. Ignition Signals: IGT: Ignition Trigger signal to the igniter.

IGF: Ignition Confirmation signal back from the igniter (crucial for fuel delivery). Fueling:

#10 / #20 (or #1 / #2): Injector pulse signals. Many 4S-FE units use "batch fire" injection. Sensors: PIM: Pressure Intake Manifold (MAP sensor signal). THW / THA: Water and Intake Air temperature signals. OX: Oxygen sensor signal. 🛠️ Troubleshooting & Resources

Cross-Compatibility: If you cannot find a specific 4S-FE diagram, the 3S-FE wiring from the same year and chassis is almost identical in pin assignment.

Connector Identification: Always count pins from the wire side of the plug (not the ECU pins) to avoid mirroring your wiring.

JDM Specifics: Many 4S-FE ECUs feature an "Econ" light or specific lean-burn pins if the engine is an "S-FE Lean Burn" variant. 🔗 Useful Links

General Toyota Diagrams: You can find high-resolution JDM wiring maps on Scribd's Toyota JDM Guide.

Forums: The CarTechnology forum has archived threads specifically requesting 4S-FE pinouts for the ST190 Corona. Toyota 4S-FE ecu pin out please - Printable Version

Toyota 4S-FE ecu pin out please - Printable Version. Toyota 4S-FE ecu pin out please - Printable Version. +- CarTechnoloGY (https: CarTechnoloGY Toyota Carina AT192 - 5A-FE ECU Pinout & Wiring Diagrams

You're looking for the ECU pinout for a 4S-FE engine!

The 4S-FE engine is a 1.8L inline-4 cylinder engine produced by Toyota, used in various models such as the Toyota Camry, Corolla, and Solara.

Here is the ECU pinout for a 4S-FE engine:

Toyota 4S-FE ECU Pinout ( 1990-1996 models)

The ECU used in 4S-FE engines from 1990 to 1996 is the Toyota ECU type " 89661-..." or " 89761-...".

Here is a basic pinout of the ECU:

Connector 1 (J1, 26 pins)

| Pin # | Signal Name | Description | | --- | --- | --- | | 1 | EGT | Engine Ground | | 2 | IGT | Ignition Timing Signal | | 3 | IGF | Ignition Feedback Signal | | 4 | GND | Ground | | 5 | +B | Battery Voltage | | 6 | THA | Throttle Angle Sensor ( TPS) | | 7 | ODO | Odometer Signal | | 8 | ISC | Idle Speed Control | | 9 | SFT | Shift Solenoid (Automatic Transmission) | | 10 | L | Fuel Pump Relay | | 11 | W | Fuel Pump Monitor | | 12 | RCO | Resistance (Resistor) Check Output | | 13 | NE | Engine Speed Sensor (CKP) | | 14 | NTC | Coolant Temperature Sensor (ECTS) | | 15 | AFS | Air/Fuel Sensor (Oxygen Sensor) | | 16 | A/F | Air/Fuel Mixture Control | | 17 | Rx | Serial Communication Receive | | 18 | Tx | Serial Communication Transmit | | 19-26 | - | Not Used |

Connector 2 (J2, 28 pins)

| Pin # | Signal Name | Description | | --- | --- | --- | | 1 | +5V | 5V Reference Voltage | | 2 | GND | Ground | | 3 | VS | Vehicle Speed Sensor | | 4 | IAC | Idle Air Control Valve | | 5 | ISC2 | Idle Speed Control (auxiliary) | | 6 | F | Fuel Injector 1 ( Cylinder 1) | | 7 | F2 | Fuel Injector 2 (Cylinder 2) | | 8 | F3 | Fuel Injector 3 (Cylinder 3) | | 9 | F4 | Fuel Injector 4 (Cylinder 4) | | 10 | IG | Ignition Coil | | 11 | - | Not Used | | 12-28 | - | Not Used |

Additional notes:

This pinout is for a basic 4S-FE engine ECU. There might be variations depending on the specific model year, trim, or region.
Consult a repair manual or wiring diagram for your specific vehicle for more detailed information.
Some signals might be missing or different depending on the ECU revision.

Keep in mind that ECU pinouts can vary across different models and years, and this information might not be applicable to all 4S-FE engines.

Would you like to know more about a specific aspect of the ECU or engine?

For mechanics, tuners, and DIY enthusiasts, understanding the 4S-FE ECU pinout is the cornerstone of successful engine swaps, troubleshooting, and performance tuning. The Toyota 4S-FE, a 1.8L member of the legendary S-series engine family, was a staple in 1990s Japanese domestic market (JDM) sedans like the Corona, Carina, and Vista.

Because the 4S-FE shares much of its architecture with the larger 3S-FE, their ECU layouts are often nearly identical, typically featuring a 26-pin and 16-pin (or 22-pin) connector configuration. Core ECU Pin Functions

The 4S-FE ECU manages everything from ignition timing to fuel injection pulses. Below is a breakdown of the critical pins and their roles in the engine management system. Power & Ground Terminals

Before testing sensors, you must verify the ECU is receiving clean power and has solid grounds. +B and +B1: Switched +12V power from the EFI main relay.

BATT: Permanent +12V feed from the battery for the ECU’s internal memory (Keep Alive Memory). 4s-fe ecu pinout

E01 & E02: Primary computer grounds (usually bolted to the intake manifold or cylinder head). E1: The main internal ground for the ECU logic circuit.

E2: The dedicated sensor ground circuit; never tap into this for high-current accessories. Ignition & Injection Signals

#10 & #20: These pins control the fuel injectors. On the 4S-FE, these are often "batch-fired" in pairs (1 & 3, 2 & 4).

IGT (Ignition Timing): The output signal sent from the ECU to the igniter to trigger a spark.

IGF (Ignition Feedback): A crucial "confirmation" signal sent back from the igniter to the ECU. If the ECU doesn't see IGF, it will cut fuel to prevent catalytic converter damage.

STA (Starter): Informs the ECU the engine is cranking so it can provide a richer fuel mixture for starting. Critical Sensors

PIM (Pressure Intake Manifold): The MAP sensor signal. This is the primary input the ECU uses to calculate engine load and fuel requirements.

THW (Coolant Temperature): Monitors engine heat to adjust fuel trim and idle speed.

THA (Intake Air Temp): Often integrated into the MAP sensor or air box to account for air density.

OX (Oxygen Sensor): Provides feedback on the air-fuel ratio to keep the engine in "closed loop" efficiency.

NE (Engine Speed/RPM): The signal from the distributor or crank sensor that tells the ECU how fast the engine is spinning. Diagnostic Pins: The TE1 and E1 Bridge

On older Toyota ECUs like the 4S-FE, you don't need a modern OBDII scanner to read codes.

Locate the "Diagnostic" or "Check" connector in the engine bay. Bridge pins TE1 and E1 with a paperclip. Turn the ignition to ON (don't start the engine).

Count the flashes of the "Check Engine" light to read the 2-digit fault codes. Common Wiring Variations

While most 4S-FE engines use a standard Toyota S-series wiring logic, variations exist between early (distributor) and late (distributorless/waste-spark) models. Always verify your specific ECU part number—usually a 10-digit number like 89661-XXXXX—against a Toyota Terminal Guide to ensure you aren't looking at a 4E-FE or 5A-FE diagram, which look similar but have different pin assignments.

Which specific vehicle model or ECU part number are you working with for this 4S-FE project?

engine is a 1.8L member of Toyota's "S" family, commonly found in 1990s models like the Corona, Carina, and Camry/Vista . Because it shares a block design with the 2.0L

, their ECU pinouts are often identical or highly similar, making 3S-FE diagrams a standard reference for 4S-FE troubleshooting. Core ECU Pinout Identification Most 4S-FE ECUs use a 26-pin / 16-pin / 22-pin

multi-plug configuration. Below are the critical terminals for engine management: Typical Wire Color Function & Connection Black-Yellow Switched 12V power from the EFI main relay. White-Green Constant 12V battery power for ECU memory. Primary computer ground. Brown-White Sensor signal ground. Green / Yellow Injector pulse signals (usually paired 1&3 and 2&4). Black-White Ignition Timing signal sent to the igniter.

Ignition Feedback signal from the igniter to confirm firing. Green / Blue Engine speed (RPM) signal from the distributor pickup. Light Green Pressure Intake Manifold (MAP sensor) signal. Green-Black Engine Coolant Temperature (ECT) sensor signal. Oxygen sensor signal (Lambda). Diagnostic and Auxiliary Terminals Technicians often use these pins at the Check Connector

(DLC) or directly at the ECU to read codes and test systems: TE1 / TE2:

Diagnostics "Test" terminals. Shorting TE1 to E1 triggers "Check Engine" light flash codes. Speed signal from the instrument cluster (VSS). Starter signal used to enrich fuel during cranking. Throttle Position Sensor (TPS) idle contact signal. Key Differences: 4S-FE vs. 3S-FE While the wiring is nearly identical, the ECU fuel maps

differ. Using a 3S-FE ECU on a 4S-FE engine may lead to rich running conditions because the 3S-FE is tuned for a larger displacement (2.0L vs 1.8L). Physically, 4S-FE engines often have different sensor locations, such as the engine number being near the oil filter rather than the side of the block. 4E-FE ECU Pinout and Wiring Details | PDF - Scribd

Electrical Load Signal System. Taillight Relay. AC2. Unknown. 12V To Aircon Computer. TE2. White-Blue. Check Connector. TE1. Gray.

Final Thoughts

The 3S-FE ECU is a robust unit from the golden era of Toyota reliability. But 30-year-old wiring gets brittle. Before you blame the ECU, check your grounds and your corrosion.

Print this pinout, tape it to your toolbox, and save yourself three hours of squinting at a blurry PDF.

Got a specific 3S-FE pinout question? Drop your ECU part number in the comments below.

Finding a verified 4S-FE ECU pinout can be tricky since these JDM engines (commonly found in the Toyota Corona, Carina, and Mark II) vary slightly by year and chassis (e.g., ST180 vs. ST190).

However, because the 4S-FE and 3S-FE share the same S-series engine architecture, their ECUs often use the same 26-pin / 16-pin / 22-pin or 12-pin / 16-pin / 26-pin connector configurations. Common Toyota "S-Series" ECU Pinout (Standard Layout)

The following pin descriptions are typical for 1990s-era S-series FE engines using a Manifold Absolute Pressure (MAP) sensor. Power & Ground Pins

BATT (Back-up Power): Provides constant 12V for the ECU memory.

+B / +B1 (Switch Power): 12V power from the EFI relay when the ignition is ON.

E01 / E02 (Power Ground): Heavy-duty grounds for injector drivers.

E1 (Logic Ground): Primary ground for the ECU's internal logic.

E2 / E21 (Sensor Ground): Dedicated clean ground for sensors (MAP, TPS, Coolant). Signal Inputs PIM (Pressure Intake Manifold): Signal from the MAP sensor.

THW (Water Temp): Signal from the Engine Coolant Temperature (ECT) sensor.

THA (Air Temp): Signal from the Intake Air Temperature (IAT) sensor.

VTA (Throttle Position): Signal from the Throttle Position Sensor (TPS).

IDL (Idle Switch): Informs the ECU that the throttle is fully closed.

NE / G (Engine Speed/Position): Signals from the distributor/crank sensor for RPM and timing. Control Outputs

#10, #20 (Injectors): Grounding signals to fire the fuel injectors.

IGT (Ignition Timing): Trigger signal sent to the igniter to fire the coil.

IGF (Ignition Feedback): Signal back from the igniter confirming the coil fired (required to keep the fuel pump running).

ISC / ISCV (Idle Speed Control): Controls the idle air control valve.

W (Check Engine Light): Grounds this pin to illuminate the MIL on the dash. Drafting Your Post If you are sharing this on a forum or social media, The story of the Toyota 4S-FE ECU is

Post Title: Toyota 4S-FE ECU Pinout Reference (ST180/ST190/SX90)

Body:Hey everyone, I know how hard it can be to find solid documentation for the 4S-FE, especially for wiring swaps or troubleshooting sensor issues. Since the 4S is essentially the smaller brother of the 3S-FE, many of the pins are identical. Quick Reference for the 26P-16P-22P Layout: Need Power? Check BATT (Constant) and +B (Switched).

No Spark? Verify IGT is sending a signal and the ECU is receiving IGF.

Rich/Lean Issues? Test the PIM (MAP sensor) and THW (Coolant temp) signals.

Pro-Tip: Always verify your specific plug shape. Toyota switched between "square" and "round" terminal styles in the early '90s. If your wire colors don't match standard 3S diagrams, focus on the pin position rather than the insulation color!

Does anyone have a high-res scan for a 1994 Corona (ST190) specifically? Drop it below! #Toyota #4SFE #3SFE #ECU #Wiring #JDM #EngineSwap

For a specific diagram, you might check community threads like those on ToyotaNation or the Toyota Owners Club, where users frequently share manual scans.

Toyota 4S-FE engine, part of the S-family, was commonly found in Japanese market vehicles like the Corona, Carina, and Mark II

during the early 1990s. Since these engines often used different ECU configurations depending on the specific model and year (e.g., ST180 vs. ST190), the pinout is typically categorized by the number of pins on the ECU connectors. Common ECU Pinout Configurations Most 4S-FE ECUs feature a 3-plug design (typically 26p-16p-22p 10p-18p-14p

). Below is a guide to the primary pins you will need for wiring or diagnostics: Power & Ground : Switched 12V power from the EFI main relay. : Constant 12V from the battery (for ECU memory). E1 / E2 / E01 : Main chassis and sensor grounds. Ignition & Fuel : Ignition trigger signal to the igniter. : Ignition confirmation signal back to the ECU.

: Injector pulse signals (usually batch-fired on these older units). : Intake manifold pressure signal (MAP sensor). : Intake air temperature. : Coolant temperature. : Throttle position sensor (TPS) and idle switch. : Oxygen sensor signal.

: Crankshaft/Camshaft position signals from the distributor. ISC / ISCV : Idle Speed Control Valve.

: Fuel pump relay control (often grounds the circuit to turn the pump on). : Check engine light (MIL) output. Diagnostic Access

To retrieve error codes without a scanner, you can bridge the following pins in the "Diagnosis" box under the hood: : Bridge these with a paperclip. Ignition ON

: Count the flashes of the "Check Engine" light on the dash. Document Resources

For a detailed visual diagram, enthusiasts generally refer to the Toyota ST190/ST191 Repair Manual

Toyota Corona/Carina (1992–1996) Electrical Wiring Diagrams

. You can find community-verified spreadsheets and high-resolution photos of these pinouts on: Toyota-Club.net (Technical database for JDM Toyotas). ToyoDIY.com (Parts cross-referencing). for a particular car model, like a Corona ST190

A deep dive into the 4S-FE ECU pinout!

The 4S-FE is a 1.8L inline-4 engine produced by Toyota, used in various models such as the Camry, Corolla, and Solara. The ECU (Engine Control Unit) for this engine is a complex computer that controls various engine functions, including fuel injection, ignition timing, and emissions.

Here's a detailed breakdown of the 4S-FE ECU pinout:

ECU Pinout Overview

The 4S-FE ECU has a total of 35 pins, which are divided into several categories:

Power and ground pins (5)
Sensor input pins (10)
Actuator output pins (10)
Communication pins (5)
Miscellaneous pins (5)

Power and Ground Pins

B+ (Pin 1) - Battery positive voltage (12V)
B- (Pin 2) - Battery negative voltage (Ground)
IG (Pin 3) - Ignition switch voltage (12V)
E1 (Pin 4) - Engine ground
E2 (Pin 5) - Chassis ground

Sensor Input Pins

TPS (Pin 6) - Throttle position sensor (0-5V)
IAT (Pin 7) - Intake air temperature sensor (0-5V)
ECT (Pin 8) - Engine coolant temperature sensor (0-5V)
O2 (Pin 9) - Oxygen sensor (0-1V)
CKP (Pin 10) - Crankshaft position sensor (0-5V)
CMP (Pin 11) - Camshaft position sensor (0-5V)
VSS (Pin 12) - Vehicle speed sensor (0-5V)
KS (Pin 13) - Knock sensor (0-5V)
MAP (Pin 14) - Manifold absolute pressure sensor (0-5V)
AFM (Pin 15) - Airflow meter (0-5V)

Actuator Output Pins

Fuel injector 1 (Pin 16) - Fuel injector control (12V)
Fuel injector 2 (Pin 17) - Fuel injector control (12V)
Fuel injector 3 (Pin 18) - Fuel injector control (12V)
Fuel injector 4 (Pin 19) - Fuel injector control (12V)
Ignition coil 1 (Pin 20) - Ignition coil control (12V)
Ignition coil 2 (Pin 21) - Ignition coil control (12V)
Idle air control valve (Pin 22) - Idle air control (12V)
Fuel pump relay (Pin 23) - Fuel pump control (12V)
A/C relay (Pin 24) - A/C control (12V)
Fan relay (Pin 25) - Cooling fan control (12V)

Communication Pins

Diagnosis line (Pin 26) - Diagnosis line (K-line)
Serial communication line (Pin 27) - Serial communication line (CAN bus)
Immobilizer line (Pin 28) - Immobilizer communication line
Fuel pump line (Pin 29) - Fuel pump communication line
A/C line (Pin 30) - A/C communication line

Miscellaneous Pins

Service check line (Pin 31) - Service check line
Mil/Check engine light (Pin 32) - Malfunction indicator lamp
Fuel trim line (Pin 33) - Fuel trim line
Knock control line (Pin 34) - Knock control line
Not used (Pin 35) - Not used

Keep in mind that this is a general overview, and actual pinouts may vary depending on the specific ECU and vehicle model. Always consult the repair manual or ECU documentation for specific information.

Would you like to know more about a specific aspect of the 4S-FE ECU or have any questions about the pinout?

The Toyota 4S-FE engine is a 1.8L inline-four from the legendary S-series family, common in 1990s models like the Corona, Carina, and Mark II. Because it shares its architecture with the more famous 3S-FE, many of its ECU pinout abbreviations and wiring logics are identical.

If you are working on a swap or troubleshooting, the most reliable way to identify pins is to look for the abbreviations printed directly on the ECU circuit board (PCB) next to the connector pins. Common 4S-FE ECU Pin Abbreviations & Functions

While specific wire colors can vary between car models (e.g., a Mark II vs. a Carina), the following terminal codes are standard for Toyota ECUs of this era: Full Name / Function +B / +B1 Switched Power +12V power from the EFI Main Relay when the ignition is ON. BATT Constant Battery Power Permanent +12V used to keep the ECU memory (DTCs) alive. E1 / E01 Main Ground The primary computer and power grounds for the ECU. E2 / E21 Sensor Ground

Dedicated ground loop for sensitive sensors to prevent electrical noise. #10 / #20 Injector Signals

Controls the ground side of the fuel injectors (usually batch fired). IGT Ignition Timing Signal sent from the ECU to the igniter to trigger a spark. IGF Ignition Feedback

A "confirmation" signal sent back to the ECU to prove a spark occurred. NE / NE- Crank/Cam Signal Engine speed (RPM) and position data used for timing. PIM Pressure Intake Manifold Signal from the MAP sensor to measure engine load. THW Water Temp Signal Engine Coolant Temperature (ECT) sensor input. THA Intake Air Temp Measures the temperature of the air entering the engine. VCC Sensor Power

5V reference power supplied by the ECU to sensors like the TPS. IDL / VTA Throttle Position

Signals for idle switch (IDL) and variable throttle angle (VTA). OX / HT Oxygen Sensor Feedback from the O2 sensor; "HT" is for the sensor heater. STA Starter Signal

Tells the ECU the engine is cranking to enrich the fuel mixture. W Warning Light Controls the "Check Engine" light on the dashboard. Pinout Configuration (26P - 16P - 22P)

Many 4S-FE models utilize a triple-connector setup. A common configuration found in 90s Toyotas like the Celica and ST202 with the S-series engine includes:

26-Pin Connector: Often contains main power (+B, BATT), grounds (E1, E01), and primary sensor inputs (PIM, THW).

16-Pin Connector: Typically handles auxiliary systems like A/C, speed sensors (SPD), and diagnostic ports (TE1, TE2).

22-Pin Connector: Frequently dedicated to ignition and fuel delivery (IGT, IGF, Injectors). Troubleshooting Tip: Checking the Board

If your harness colors don't match the diagrams you find online, unscrew the ECU casing and look at the bottom of the PCB. Toyota almost always silk-screens the pin names (like "BATT", "E1", "PIM") directly onto the board near the pins. This is the "gold standard" for ensuring you don't fry your computer during a custom wiring job. If you'd like, let me know: The exact car model and year (e.g., 1994 Toyota Corona) The part number on your ECU (e.g., 89661-xxxxx) The connector count (Is it 2-plug or 3-plug?)

The Toyota 4S-FE is a 1.8-liter inline-four engine known for its reliability in 1990s sedans like the Corona, Carina, and Caldina. If you are performing an engine swap, diagnosing a no-start condition, or installing an aftermarket piggyback controller, understanding the 4S-FE ECU pinout is essential. This pinout is for a basic 4S-FE engine ECU

Because the 4S-FE was produced across several generations, the wiring can vary between the early "flat plug" OBD1 style and the later "vertical" connector styles. This guide focuses on the common 26-pin, 16-pin, and 22-pin configurations found in early-to-mid 90s models. Understanding the Connector Layout

Most 4S-FE ECUs utilize a three-plug system. When looking at the ECU pins (not the wire side), the plugs are generally labeled from left to right. Plug A (26-pin): Mostly engine sensors and injectors. Plug B (16-pin): Power, ground, and ignition signals.

Plug C (22-pin): Transmission controls and auxiliary signals. Key Power and Ground Pins

Before testing sensors, you must ensure the ECU is receiving power and has a solid path to the ground.

+B and +B1: These are the main power feeds from the EFI relay. They should show 12V when the ignition is ON.

BATT: This is constant 12V power from the battery used for memory. If this wire is cut, your car may run but will lose "learned" idle data every time you turn it off.

E1, E2, E21: These are ground pins. E1 is the main chassis ground, while E2 is a dedicated ground for sensors like the TPS and Coolant Temp.

EO1, EO2: These are power grounds specifically for the high-current injector drivers. Essential Sensor Inputs

If your engine is cranking but not starting, these are the pins you should probe with a multimeter or oscilloscope:

NE+ and NE- (Crankshaft Position): These provide the RPM signal. Without this, the ECU won't fire the injectors or the coil.

G1 and G2 (Camshaft Position): Used for cylinder identification and sequential injection timing.

THW (Coolant Temperature): High voltage here usually indicates a cold engine; low voltage indicates a warm engine. A fault here often causes a very rich or lean condition.

PIM (Manifold Absolute Pressure): The 4S-FE typically uses a MAP sensor rather than an AFM. This pin tells the ECU how much load the engine is under.

VTA (Throttle Position Sensor): Signals the angle of the throttle plate. Output Control Pins

These pins are where the ECU "talks" to the engine components:

#10, #20 (Injectors): These pins ground the injectors to spray fuel. Note that many 4S-FE setups use "batch fire" injection, where injectors are paired.

IGT (Ignition Timing): This is the trigger signal sent to the igniter to fire the spark plugs.

IGF (Ignition Feedback): The igniter sends a signal back to the ECU on this pin to confirm the coil fired. If the ECU doesn't see IGF, it will cut fuel for safety.

ISC (Idle Speed Control): Controls the bypass valve to maintain a steady idle under load (like when the AC is on). Troubleshooting Tips

Check for Voltage at +B: If you have no power at the +B pin, check your EFI fuse and the EFI relay.

Verify Sensor Grounds: Ensure there is zero resistance between the E2 pin and the sensor connectors. A bad ground can cause "ghost" sensor codes.

Check for Spark (IGT/IGF): If you have no spark, check the IGT signal. If you have spark for one second and then it dies, your IGF signal is likely missing.

Note: Always cross-reference your specific ECU part number (e.g., 89661-2Bxxx) as Toyota made subtle changes to wire colors and pin locations depending on whether the vehicle was an automatic or manual, and which specific chassis it was installed in.

The Toyota 4S-FE ECU pinout serves as a technical map for the Engine Control Unit (ECU) of the 1.8L 4S-FE inline-four engine, commonly found in vehicles like the Corona and Carina. This map identifies the specific functions of each terminal on the ECU connectors, which is essential for engine swaps, troubleshooting sensor issues, or installing aftermarket piggyback controllers.

The 4S-FE ECU generally utilizes a multi-plug configuration (often 26-pin and 16-pin or similar variations depending on the production year) to manage fuel injection, ignition, and idle speed. Core Pinout Functions

Below are the critical signals and pins typically found on 4S-FE engine control units, categorized by their system role: Power and Ground

+B / +B1: Switched battery power (12V) supplied from the EFI main relay. BATT: Continuous 12V battery power for memory storage. E1 / E01 / E02: Main computer and power grounds.

E2: Sensor ground, used for clean signals from components like the coolant temperature sensor. Ignition System

IGT: Ignition Timing signal sent from the ECU to the igniter to trigger a spark.

IGF: Ignition Feedback signal sent back to the ECU to confirm the spark actually occurred.

NE / NE-: Crankshaft or distributor RPM signals used to determine engine speed and position. Fuel and Air Management

#10 / #20: Injector pulse signals; typically, 4S-FE engines use batch fire injection where pins control pairs of injectors (1 & 3, 2 & 4).

PIM / VG: Pressure Intake Manifold (MAP sensor) or Mass Air Flow signal used to calculate engine load. THA: Intake Air Temperature sensor signal. THW: Engine Coolant Temperature signal.

OX / OX1: Oxygen sensor signal for closed-loop fuel trimming. Throttle and Idle Control VCC / VC: 5V constant power supply to the sensors.

VTA / PSW: Throttle Position Sensor (TPS) signal indicating how far the butterfly valve is open.

IDL: Idle switch signal that tells the ECU the throttle is fully closed.

RSC / RSO: Rotary Solenoid signals for controlling the Idle Air Control (IAC) valve. Diagnostic and Auxiliary Pins

TE1 / TE2: Diagnostic test terminals; jumping TE1 to E1 in the diagnostic box allows for reading error codes via the check engine light. W / Check Engine: Output for the dashboard warning light. SPD: Vehicle Speed Sensor (VSS) signal.

STA: Starter signal, informing the ECU that the engine is cranking. Troubleshooting Tips ECU Connectors Everything You Need to Know

1. Leaking Capacitors (The Silent Killer)

Symptoms: Random misfires, erratic idle, transmission shifting hard (AT), no start. Fix: Open the ECU. Look for electrolytic capacitors (cylindrical components) near the harness plug. If they are leaking brown/black goo onto the circuit board, you need immediate repair. Action: Desolder and replace all capacitors (typically 100µF, 220µF, 470µF values). Clean the board with isopropyl alcohol.

Plug A (16 pins) – Power & Actuators

Understanding the 4S-FE Engine Management System

Before we dive into the pinout chart, it is essential to understand what you are dealing with. The 4S-FE uses Toyota’s TCCS (Toyota Computer Controlled System). Unlike modern CAN-bus systems, the 4S-FE ECU is relatively simple. It relies on analog sensors, a distributor-based ignition system, and a batch-fire fuel injection setup.

Plug B (12 pins) – Sensors (5V Reference)

| Pin | Wire Color | Function | Signal Type | Voltage/Note | | :--- | :--- | :--- | :--- | :--- | | B1 | Gray | Throttle Position Sensor (VTA) | 0.3 – 4.8V | Closed = 0.3V / WOT = 4.8V | | B2 | Green | TPS Reference Voltage (VC) | 5V ± 0.1V | Supplied by ECU | | B3 | Brown | TPS Ground (E2) | 0V | Sensor ground | | B4 | Red-Yellow | Intake Air Temp (THA) | 0.5 – 3.5V | Cold = high voltage | | B5 | Blue-Black | Engine Coolant Temp (THW) | 0.2 – 3.5V | Hot engine = ~0.5V | | B6 | (Empty) | N/A | N/A | N/A | | B7 | Black-Blue | MAP / VAF Sensor (PIM) | 1.5 – 4.5V | Idle = 1.5V / WOT = 4.0V | | B8 | Green-Red | MAP/VAF 5V (VCC) | 5V | Sensor power | | B9 | White-Black | MAP/VAF Ground (E2) | 0V | Sensor ground | | B10 | Black-Red | Idle Air Control Valve (RSC) | +12V | IACV coil #1 | | B11 | Black-Yellow | Idle Air Control Valve (RSO) | +12V | IACV coil #2 | | B12 | (Empty) | N/A | N/A | N/A |

1. The "No Spark" Mystery

If you have fuel but no spark on a 4S-FE, check the IGT (Ignition Timing Signal) and IGF (Ignition Feedback Signal) pins.

The ECU sends an IGT signal to the igniter (coil pack driver).
The igniter sends an IGF signal back to the ECU to confirm the spark happened.
If the ECU doesn't receive IGF, it cuts fuel to prevent flooding.

Swapping or Converting to Standalone ECU

Many enthusiasts swap the 4S-FE into older RWD cars (KE70, TE71) or upgrade to a standalone ECU (e.g., Megasquirt, Speeduino, or Link). Using the pinout above, here is what you need to retain:

Keep: MAP sensor (easy to calibrate), IAT, CLT, TPS (variable type).
Modify: Injectors (wired to standalone high-impedance drivers). The 4S-FE injectors are high impedance (~13.8 ohms) – no ballast resistors required.
Replace: Distributor pickup (use a 36-1 trigger wheel or retain distributor for batch fire).
Delete: ISC valve (use a simple PWM idle valve or manual idle screw).

When building a new harness for a standalone, you only need:

Power (12V constant + 12V switched)
Ground (ECU ground direct to engine)
Crank/cam signal
TPS, MAP, IAT, CLT
Injector outputs (4x)
Ignition output (single channel for distributor or wasted spark)

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