2004 Subaru Outback Lost Accelerator (ULEV)



Left for work yesterday AM on a “dark and stormy” morning. About 1/2 mile down the road lost my accelerator. Engine was running fine, but pushing pedal did nothing. Engine check light “ON”. Opened hood and found a small mouse nest on top of throttle body. Came back after work. Looked for chewed cables, none found. Car started up and accelerator worked, drove home, hooked up code reader, P0138: downstream O2 sensor, high voltage.
What could it be?
Accelerator Pedal Position Sensor?

PS: trapped a mouse in the garage last night…one down 5,789 to go!


Those “dark and stormy nights, or mornings in this case” that Tom and Ray talk about can really be bad news to the car owner. LOL

The P0138 code refers to the O2 sensor after the CAT for bank 1. It is seeing a rich mixture for some reason. Here is a link to refer to:


The trouble you described seemed to be sudden, like power to the TPS sensor was being interrupted but no code was generated to indicate that. I suggest you check the codes again to see if the code has cleared or is now pending.


Something – either the O2 sensor or TPS or some other problem – may have convinced the ECM to put the engine in a special mode (usually called “limp mode”) that only allows low speed driving. It doesn’t matter how much you press on the pedal, the car won’t go faster than its limp-mode speed. It’s done to protect the engine (and driver presumably) until the problem is resolved. I wouldn’t think an O2 sensor problem at that location would cause a limp mode, but maybe it does. If it was a TPS problem, usually that would at least set a pending code. Did you read out both the pending and active codes?


Ah, the rare ULEV model!
I always wonder why companies bother to label this on their cars when the general public has no idea what it means, and wouldn’t care if they did.