P2127 code on a Focus XR5/Focus ST

I had an issue with my 2007 Ford Focus XR5 (aka Focus ST) recently.

I started getting a ‘Steering Assist Failure‘ message appear occasionally when starting my car. Usually I could just turn if off, leave it for a little while then start again and it would be OK, and the car would be behave normally.

Shortly after I got an ‘Engine Systems Fault‘ message and the car entered ‘Low Acceleration Mode‘ to protect itself. Using my OBD-II adapter and the ‘Torque’ Android app, I found the specific error to be:

P2127 – Throttle/Pedal Position Sensor/Switch ‘E’ Circuit Low

Using the magic powers of Google, I found this:

“Finally the P2127 error code was sorted.

When the car is started in the morning the voltage drops below 9v.

9v is the threshold voltage for the all the ECU sensors, first sensor on my car that then schemes there’s [email protected] in the land is the throttle position sensor.”

Using my very cheap multimeter, I tested the load across the battery. When I turned the key, sure enough, the voltage dropped from 12.43V to 8.3V, sending the throttle position sensor into an error state. Testing the same thing on Bek’s car showed it dropped to about 10.5V which is much healthier.

Once I installed a new battery, everything worked perfectly.

Hopefully this might help someone else, although I’m sure a different type of car would exhibit different symptoms.