Subaru Forester Electronic Throttle faults p2109


Subaru Forester 2004 ej25 turbo series 1


The vehicle drove into the workshop running poorly at that but running, the client advised that if he cleared the fault codes related to the throttle he would be able to drive it a little while before it goes into limp mode.


We took a look that the fault codes and found that the fault code would not clear P2109 “Throttle / Pedal Position Sensor A Minimum Stop Performance”. Not understanding too much about how the subraru electronti throttle control worked, we decided that we should sue the scope to measure what is happening at the throttle control motor.
The scope verified that there was power to tps switches and that the throttle position switch was showing a normal reading, we turned the scope now to the power circuits and found no ECU control of the throttle actuator, Could this be the ecu is switching off the control circuit due to high current draw on the throttle motor, we shut down the engine and with the scope still connected started the engine and foudn that there was never a signal to the throttle motor, Time for a wiring diagram.

Consulting with the wiring diagram showed that the ECU has inputs and outputs for throttle control, the inputs such as throttle control relay and outputs for the duty cycle of the throttle actuator

“before you can get an output you must have an input”                                  2004-Forester-Electronic-Throttle-Control-relay

We happened to get lucky and cycled the ignition and found that the relay circuit was being controlled by the ecu, the ecu would switch on the throttle relay for a split second before shutting it down, with this in mind we decided to manually make the relay stay on and see if the vehicles throttle actuator would operate, no such luck, we installed a new relay and continued on, before condemning the ECU, the wiring from ecu to the throttle control actuator should be checked any shorts to ground. After confirming that there was no integrity issues with the wiring we rang around all the wreckers to find an ecu, after several hours searching we found an ecu,


The particular ECU needs to be programmed, the client found a mobile guy that comes around and will program the ECU, a practical lesson learned on programming ECU’s

“Make sure you Put the same part number in”.                                                  Forester-Throttle-Control-Actuator

after a new ECU was Programmed the Vehicle started and the throttle actuator was operational, after this was the clean up and clear the faults, carry out a test drive before ring the client to let him know the vehicle was ready.


Always test what you can get to before replacing unnecessary parts, make sure you test all the wiring before calling for a new ecu, including the throttle actuators resistance.

Wiring Diagram