The Engine Control Module (ECM) fitted to the 2004 Subaru Impreza WRX STI uses a five-connector harness on the turbocharged H4DOTC horizontally-opposed 2.0 litre engine, as documented in Fuji Heavy Industries service manual G1870GE3. The ECM serves both the WRX and WRX STI within the GD/GG chassis family and is located under the steering column inside the instrument panel lower trim panel. Connectors are designated B134 (28-pin), B135 (22-pin), B84 (31-pin), B136 (17-pin), and B137 (24-pin); the wiring section (G1870GE7) explicitly distinguishes the turbo (TB) engine model subset from the naturally-aspirated variant. The 2005 Saab 9-2X Aero, a rebadged US-market WRX, shares the same ECM connector arrangement.
ECU - Electronic Control Unit Connector.
Connector B134
| Pin | name | Signal |
|---|---|---|
| 23 | Engine Speed Output Sensor | RPM |
Connector B135
| Pin | name | Signal |
|---|---|---|
| 1 | Power Ground | Ground |
| 27 | Vehicle Speed Sensor | Speed |
Connector B136
| Pin | name | Signal |
|---|---|---|
| 8 | Brake Switch 2 | Analog |
| 9 | Brake Switch 1 | Analog |
| 13 | Intake Air Temperature Sensor | Analog |
| 17 | Accelerator Position Sensor | Analog |
| 18 | Electric Throttle Sensor | Analog |
| 21 | Fuel Tank Pressure Sensor | Analog |
| 22 | Manifold Absolute Pressure Sensor | Analog |
| 23 | Mass Air Flow Sensor | Analog |
Notes
The ECM is located under the steering column, inside the instrument panel lower trim panel. The turbocharged engine model uses all five connectors (B134, B135, B84, B136, B137); the naturally-aspirated model uses only B134, B135, and B136. Disconnecting the battery before removing the ECM is required to avoid damaging the fuel injection system; the ECM must be replaced with a unit of the correct specification. Sensor power supply is 5 V at B84-3; battery backup (memory) power is always live at B84-10 (10–13 V); main control-unit power supply is 12 V ignition-on at B84-2.
Signals
- Engine Speed Output Sensor — crankshaft rotational speed signal output from the ECM (B134-23)
- Power Ground — ECM power ground return (B135-1)
- Vehicle Speed Sensor — vehicle speed signal input to the ECM (B135-27)
- Brake Switch 2 — secondary brake switch analogue input (B136-8)
- Brake Switch 1 — primary brake switch analogue input (B136-9)
- Intake Air Temperature Sensor — IAT signal input; sensor is integrated with the mass air flow sensor (B136-13)
- Accelerator Position Sensor — accelerator pedal position signal input (B136-17)
- Electric Throttle Sensor — electronic throttle position signal input (B136-18)
- Fuel Tank Pressure Sensor — evaporative emission fuel tank pressure signal input (B136-21)
- Manifold Absolute Pressure Sensor — MAP sensor signal input for boost and load calculation (B136-22)
- Mass Air Flow Sensor — MAF sensor signal input for air-mass measurement (B136-23)