e40 random and very intermittent P2138 and reduced power

I have a LS2 in a swap application with a non-GM manual transmission.

I am using an 2005 e40 PCM, I actually have 2, and both have been SPS flashed as 05 GTO. I have a gold blade LS3 throttle body on it. The car runs very well and I have several thousand miles on it. No problems tuning it at all.

The issue is that occasionally, probably every 50 miles or so but there is no clear pattern (although it only seems to happen at start up or at idle , never at WOT), I get a P2138 and reduced power with a dead pedal. One time it happened tweice in 10 minutes, most recently it went for 5 days of daily driving without throwing the code.

I was using a c7 pedal but switched to a C6 pedal with no change. I scanned all of the APP and TPS channels and nothing ever looks strange although I have never caught it in the act when it threw the code.

The problem is the same with each PCM.

If it was a wiring problem I would expect a little more consistency - I have moved, shaken and pulled on every relevant wire while the car is running and I can not make it throw the code, but driving around town it will randomly pop up.

Any ideas? I am not sure what the next step should be.

I have a 2005 Colorado with a V8 swap running an E40 programmed as a 06 SSR manual trans. Ran into the same issue as you describe trying to tune it on the dyno. It got so bad the tuner gave up and said he couldn't help me. That inspired me to buy HP Tuners and do it myself, but I digress.

What I did to fix it was to change throttle bodies. I had an LS2 TB but for whatever reason it would randomly go into reduced power and dead pedal. The harness was brand new but despite the fact I still checked and rechecked connections and wiring. Finally, I swapped the LS2 for a TBSS throttle body I had laying around. No issues since.

I have a gold blade as well but never used it with this combo. In my research on other model specific forums, I read about LS2 cars having issues with the gold blade TB's. Some worked, most didn't. FWIW

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Originally Posted by MainstreaM

I have a 2005 Colorado with a V8 swap running an E40 programmed as a 06 SSR manual trans. Ran into the same issue as you describe trying to tune it on the dyno. It got so bad the tuner gave up and said he couldn't help me. That inspired me to buy HP Tuners and do it myself, but I digress.

What I did to fix it was to change throttle bodies. I had an LS2 TB but for whatever reason it would randomly go into reduced power and dead pedal. The harness was brand new but despite the fact I still checked and rechecked connections and wiring. Finally, I swapped the LS2 for a TBSS throttle body I had laying around. No issues since.

I have a gold blade as well but never used it with this combo. In my research on other model specific forums, I read about LS2 cars having issues with the gold blade TB's. Some worked, most didn't. FWIW

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Were you getting any codes other than p2138?

That is pretty interesting. I might have to give a TBSS throttle body a try.

Well I tried a TBSS throttle body and it worked great --- for about 25 miles :(


Back to the drawing board.......

Mine never threw a code which made it even more strange. Lost banks of cylinders, both fuel and / or spark. Went into reduced power, according to the dic anyway.

Is there a particular reason to use the GTO OS instead of Corvette, since you have a Corvette pedal? If nothing else it would give a little more confidence in following published diagnostics when something like this pops up.

GTO OS allows for conventional fan control and a couple of other minor things.

When I look at the freeze frame data it does indeed look like there is a mismatch; the odd thing is that we are talking 1 second of operation out of tens of thousands. I suspect that it is something in the wiring to the pedal I checked the resistance of allof the wires and 5 of the 6 wires had .6 ohms and 1 had .9 ohms. Doesn't see like a lot of difference and not enough to cause a constant problem.

Wait, why does the Corvette OS not work with Discrete fans? Do you know this because you've tested it and found it doesn't work, or just assuming because the stock setting is PWM Electric? The '05 & '06 Trailblazer E40 is PWM EV fan stock but will run both PWM Electric and Discrete fans just fine, just change the fan settings to match the config.

A static ohms test of the wiring between ECM & APP... I can't even. You will need an oscilloscope, or the services of someone who has one and knows what to do with it. But if it were me I would not even touch it knowing the APP & OS are mismatched.

Also, I just remembered the GTO is its own separate Service Number E40 and not shared with anything else. If you tried a Corvette OS on a GTO-ony Service Number, that might explain stuff not working. I would not be trying to use any oddball GTO parts unless you use ALL GTO parts. Mix-n-match is not your friend here.

The SPS flash of both of my E-40 PCMs to the 05 GTO spec was not problematic, both were from 05 Corvettes.

I did not say that a test of the resistance of the wires was a definitive test. I always thought that when trying to diagnose a problem you would start with the things that are simple and easiest to do first - I suppose I should have hired a team of calibration engineers and set up a 50 channel oscilloscope to see what is going on.

Every aspect of the PCM runs perfectly except for the mismatch between APP1 and APP2 which happens for under a second out of tens of thousands of seconds.

You have a ECM/OS mismatch AND a OS/APP mismatch, and the only symptom is an occasional DTC? You should go buy a lottery ticket.