Accelerator Pedal Codes - P012023 P012038

[jadnhm]

I have been getting these two codes for some time

• P012023 Throttle/Pedal Position Sensor A Circuit. General Signal Failures. Signal stuck low
  P012038 Throttle/Pedal Position Sensor A Circuit. FM (Frequency Modulated) / PWM (Pulse Width Modulated) Failures. Signal

I am getting the messages on the dash that says "Engine System Service Urgent" and "Engine System Service Required"

I pulled the accelerator pedal aassembly apart a bit and found it was completely solid state and there was nothing to clean and nothing smelled burt or anything... I assumed I needed a new pedal assembly.

I just got a new assembly on the car the other day and the ECM is still showing these messages. I'm a little frustrated and unsure of how to proceed.

VIDA doesn't provide much help except to say "check the wiring" basically.

I have the wiring diagram, which /does/ give me an indication of what wires lead where, but apart from the ground wire this is not really helpful in determining what /should/ be on each line... I can see where the pedal assembly is connected to the ECM on a particular wire, ground on another, and a set of wires connect to the CEM.

Judging from this wiring information and the pedal assembly codes I'm guessing there is some kind of fancy PWM signal directly to the ECM and a lower resolution 'backup' signal over CAN to the CEM?

Anyone who's experienced anything like this in a P3 car, or anyone else that could provide some insight - I would be very happy to hear from you!

[jadnhm]

Judging from the wiring information and the pedal assembly codes I guessed there is some kind of fancy PWM signal directly to the ECM and a lower resolution 'backup' signal over CAN to the CEM.

I focused on the PWM set of wires on the accelerator pedal assembly. The CAN bus wires seem to be working fine - I can see the parameters change in VIDA and also the car does drive

I first checked that the ground wire Black-Green was grounded - it was.
Then I checked that the power wire Blue-Red was supplying power - it was supplying 12V.

So then I decided I needed to check continuity on the PWM signal wire from the accelerator pedal assembly to the first connector I could find. I used the Volvo wiring diagrams to track down the connector location between the CEM to ECM harness, labelled as 74/301 in the volvo wiring diagrams - it was pretty hard to find, buried underneath the passenger headlight assembly, and I had to disassemble the front bumper/clip a bit to get to it. Luckily it was pretty accessible once the bumper trim was pulled apart.

Both the wiring diagrams I got from you and the Volvo ones said I was looking for a Blue-White wire on pin 12. I checked over and over and could not get continuity on this wire, so I decided this was the culprit.

I then theorized it was perhaps shorted to ground, and tested by checking the voltage between the signal wire at the accelerator pedal assembly and the positive battery terminal, and I got a full 12V - definitely shorted to ground.

I then tested with a 'bodge' wire - I cut the PWM Blue-White signal wire at the accelerator pedal assembly and after the 74/301 harness connector, and ran a jumper wire directly. Checking in VIDA I could now see the PWM signal reporting correctly!

So I've found my problem, and I think I've decided I will now run a permanent bodge/jumper wire from the pedal assembly to the 74/301 connector - I feel like the work involved in hunting down the short in the wire harness would be substantial. I haven't done this yet, as this is our only car and it needs to be in service for my family, but I prepared the wires on either end to be jumpered and I will look for a way to nicely run my wire the next time I can get at the car.