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P0122 Fault Diagnosis on 2002 Ford F-550 Diesel: ETC Sensor Circuit Low Issue

Model: 2002 F-550 Fault Code: P0122 Posted: 2007-07-02 13:40

Hi everyone, I'm working on diagnosing a P0122 fault (ETC sensor circuit low) on my 2002 Ford F-550 diesel. All-Data isn't providing clear guidance on where to locate the electronic throttle control (ETC) unit or how to test it. Since this is a diesel model, there's no traditional throttle body or mechanical throttle plate—this makes troubleshooting more complex. I'm looking for specific diagrams and photos of the ETC system or related sensors, especially the pedal position sensor, as these are critical in diagnosing the circuit low issue. I've already tested reference voltage and ETC signal voltages, and after swapping the pedal position sensor from another vehicle, the fault persisted. The issue seems to be pointing toward the Powertrain Control Module (PCM), though I'm not certain if it's a hardware failure or a wiring problem. I've also checked for shorts in the harness, but no clear evidence was found. Ultimately, I've had the truck towed to the Ford dealership for further evaluation—now I just need to wait and see what they find.

Related fault codes
P0122
Comments (8)
Anonymous 2007-07-02 15:41

To get more accurate diagnostics, please provide your engine type and the 8th digit of the VIN. This helps identify specific model variations.

Anonymous 2007-07-03 07:34

All-Data should show the location of the throttle body or pedal position sensor—verify if it's available in your vehicle’s service manual or online resources.

Anonymous 2007-07-03 08:06

Actually, this is a diesel model without a mechanical throttle plate. The issue likely stems from the PCM or pedal position sensor circuit. I should have investigated more thoroughly before concluding it was a hardware failure.

Anonymous 2007-07-03 08:52

Even in diesel trucks, some models may still include a pedal position sensor. It's worth confirming whether this vehicle has one and where it’s located—this could be the source of the P0122 code.

Anonymous 2007-07-03 09:01

I found the pedal position sensor and tested its reference voltage and signal output. After swapping it with a known-good unit from another vehicle, the fault remained. This points strongly to an issue within the PCM or related wiring. I've now had the truck towed to the Ford dealership for a full inspection—can't afford to fix this myself at this stage.

Anonymous 2007-07-03 09:07

Be cautious: a 'circuit low' fault could indicate a short in the wiring harness rather than an ETC sensor failure. If swapping the ETC unit doesn’t resolve it, a ground or short in the wiring path should be investigated first.

Anonymous 2007-07-03 09:09

I spent considerable time checking for shorts and tracing signals, but ultimately received instructions from above to have the truck delivered directly to the Ford service center. The PCM is now being replaced—this issue is out of my hands for now.

Anonymous 2007-07-03 09:10

That's actually a smart move—sometimes the best decision is to hand it over to professionals when you've exhausted all troubleshooting steps and have no control over the outcome.