LS3 Swap No-Start p0807 CPP Circuit Low

[BigL350]

I’m making a post separate from my build thread so this gets some more attention and is searchable on its own.

So, the car, e36 M3 sedan, had an LS1/T56 and I swapped the LS1 for an LS3. I made the wiring harness myself and am using the GM E38 PCM and an e46 DBW pedal.

The engine cranks but doesn’t start. These are the codes I get:



I disabled VATS. Checked the wiring between the pedal connector and PCM, and all good. Checked wiring from the throttle body to PCM, all good. Swapped throttle bodies, no change. Wired up the GM DBW pedal, no change. The throttle opens and closes with pedal movement. After I reconnect the battery, the first time I turn the ignition on, the fuel pump will prime. The only time after that i hear the fuel pump run is when I’ve downloaded the tune to the PCM, and it does this every time. This indicates that it’s the PCM keeping the car from starting and there’s nothing wrong with the fuel pump or wiring.


Here’s where it gets interesting. I borrowed a friend’s PCM from another LS3, disabled VATS, and still no start, but there are no throttle/pedal codes, only p0807 for clutch pedal position sensor circuit low:



I know I’m not the first joker to do an LS3 swap, so I’m hoping one of you guys has been through this and has a solution. Otherwise I’m going to have to figure out how to install a CPP sensor and add the wiring for it.


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[BigL350]

It was VATS. I disabled it in HP Tuners but didn’t choose “Write Entire” when writing the changes, so it never got changed in the ECM. Lesson learned.


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[Tim Mc]

So you solved your own mystery!

Cool!