Join Date: Aug 2004
Location: Fredericksburg, VA
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Acc Pos #1/#2 (Throttle Pedal) differ in voltage by 0.4V, replaced, still P2138 code!
Sorry for the involved technical question, but I've been battling a problem on my 04 CC SE 4x4 for about 2 weeks now. I've done all the troubleshooting possible and I'm stumped. I"m hoping a tech or somebody with a lot of experience with these trucks can help me. Here is what happened and what I've done:
When I bought the truck the CEL (SES) was on. Checked codes and it was throwing a P2138. Every time it threw the code it would go into limp mode (traction light on, stuck below 1500 rpm). Service manual states to check the following:
1. Accelerator Pedal Position Sensors (ACC sensors #1 and #2)
2. TPS (TPS sensors #1 and #2)
3. Body grounds
I hooked up a Cipher and checked open/closed voltage on ACC#1 and #2 (acc pedal sensors). The voltage RANGES were within spec - about 0.5V to 4.5V (don't remember exactly but they all checked out). But then on a double check ONE of the voltages went SLIGHTLY over where it was supposed to be - about 0.1V if I remember correctly. So, I figured I'd replace the Acc Pedal (comes with sensors) since it is cheaper than a dealer diagnostic charge.
After I replaced it, and reset the engine codes, I took it for a drive. It seemed fixed. Drove it about 25 miles, then, CEL and limp mode popped on again.
Then I hooked Cipher up and did some logs while driving. I logged battery voltage, TPS #1/#2, ACC Position sensors #1 and #2, TPS Relay, and a couple other things.
What I found was that every time the CEL light popped on, ACC #1 was about 0.3-0.4V ABOVE ACC #2. I wanted to be certain since I had a BRAND NEW ACC PEDAL in there, so I also took the intake trac off and cleaned the throttle body very well, I redid the engine/body grounds, etc.
None of that has helped. Each time I drive it the ACC signals range about 0.05V-0.25V apart, and then all the sudden #2 spikes to 0.3-0.4V above #1 and the CEL light comes back on.
If I hadn't replaced the throttle pedal I would be SURE I had a bad one. But it does this with either pedal (I tried swapping the old one in). I am at a loss. I can keep throwing parts like a throttle body or ECU at it - but I feel this HAS to be in the pedal or the wiring, but I just cant figure out how.
ANY help is MUCH apprecitaed. This is very frustrating but I hat eto take it to the dealer, probably pay them list prices to throw parts at it as well.