About to replace my ignition switch on my '08 LMM Chevy Express @140k miles.... What started with a bad engine bay fuse box, followed by a blown 5V cigarette lighter fuse in the cabin fuse box preventing me from hooking up a scanner... Followed by a bad EBCM that killed my entire van (pulled it out and the right diode had burned a hole through the silicone board) van started up immediately after disconnecting it... Installed new EBCM and programmed it with the latest GM software. That got my D letter to illuminate again with gears 2 and 3, still in limp mode though and park won't light up, nor will the dash register its in park. ABS was completely fixed by replacing my engine to frame ground strap with a hefty 0guage battery cable and dielectric grease on both terminals. But I'm still stuck with gears 2 and 3. Tried replacing NSBU switch and lined it up exactly with the old one. Still only get D to light up. Also replaced shift cable for good measure, nice and tight) I then checked the code descriptions with my tech2 and the last 2 codes I'm stuck with are:
P0705 - shift range sensor circuit failed and
P0751 - shift solenoid A control circuit low voltage. I've also replaced and flashed the TCM with my licensed GM MDI 2 to no avail.
I even tried to eliminate ALL variables by swapping in a new ECM with the latest GM stock calibrations since I run a custom tune for my oversized tires... No difference in vehicle performance but managed to pull some additional codes, one possibly leading directly to the ignition switch itself: P2510 - Engine controls ignition relay feedback circuit
I'm also getting some odd codes that are constant like:
P0532- A/C refrigerant pressure sensor circuit low voltage (even though I replaced the connector and carefully spliced it on with heat shrink wrap so its moisture tight)
I've also used my wiring schematics to go around the whole vehicle and scrape clean every single ground point, including the EBCM ground to frame by the driver door, adding dielectric grease afterwards and using my digital mutlimeter to test for voltage drop
I've also gone around to each connector and cleaned it with electronic cleaner and condensed air if it had way too much dielectric grease squished in to it (the EBCM one of them, Chevy replaced the connector but slathered grease on the female side instead of the male like you're supposed to, probably what caused the first EBCM to short itself out and burn a hole in the diode)
I should mention I also have excellent brand new dual AGM starter batteries, and cleaned the grounds to both of them. I even spliced in a new 0 guage positive cable to the engine bay fusebox megafuse from the starter battery so there is literally zero voltage drop at the fuses.
I also have a brand new OEM starter... The vehicle starts up like a champ, (1 second fire ups on cold mornings) warms up great and even shifts perfectly from gears 2 and 3 on first warm up...but if I drive around and take it easy for about an hour or so the shifts will get hard, the check engine light comes on and I get the shift solenoid A valve performance code. Brand new trans fluid and filter, zero metal shavings on the magnet (recently rebuilt trans 4L85E) and I even replaced shift solenoid A (the wiring is perfect) to no avail. Using full synthetic trans fluid too, its still perfectly pink, nothing burnt. Proper fluid levels.
Its got to be the ignition switch right? Its the only thing I haven't done... And I ordered a spare acdelco off rockauto in case I ever needed it... I just hope this is it because I've been tackling this for almost 2 years, even had jaws drop when I explained to Chevy mechanics what I'd done and repaired, they of course never got anywhere and gave me 50% off after admitting I've done everything they would do and that it sounds like I'm getting close.
Wish me luck guys...
Well after much frustration, cursing, and instructions for my truck that are wrong, I finally got the ignition switch back in properly aligned (2 notches over from where the instructions on alldata told me to set it) and nothing has improved. Still no park indicator, lights up in drive but throws p0705 and p0973 for low voltage to solenoid A control circuit. I repeat: a brand new TCM, NSBU switch, ignition switch, and entirely new engine bay fusebox, and brand new batteries, have not fixed the control circuit low voltage.
At this point I might just sell it.
