J-1850 pwm

2004 Cavy 2.2 Ecotec Gas only, Manual, No CC, No ABS, W/ AC is the car in question.

I believe I fried my pcm while trying to diagnose an AC problem I was having. No voltage at relay from computer despite good circuit to PCM (Dvom verified) and the rest of the system was either brand new or cleaned thoroughly. (New compressor, oriface device, acculator, & thermistor) 5v+ to thermistor and ohmed circuit to pcm pins. Also, had no voltage at A.I.T. sensor which turned out to be bad connector to sensor.

After replacing said connector, and I reinstalled everything and the computer started trying codes for bad MAP sensor. After testing, determined no 5V+ ref @ map but good ohms on all 3 pins to pcm.

So I believe I must not have dissipated the capacitors inside the pcm long enough and fried it during all the testing. After I jumped 5v to MAP from AIT, the car would run but very poorly. No codes though.

My questions are, should I just throw in a used pcm & bcm and do the relearn for passlock OR is there a way to save some $ and test or bypass something else that I'm not thinking about?

If I do the new pcm/bcm route, would I be able to pull my current tune from the "bad" pcm and trust it enough to load onto the new? The reason I ask is because I have a pcm& bcm from an auto trans w/ abs & cc car but I'd rather not have to deal with the service light illuminating from my current car not having those systems and also clutch release signal might not be able to be understood by the automatic trans tune.

Thanks guys.

You have more than likely a 5 volt rail(reference) shorting to ground causing the voltage to drop. Seen something similar with a DPFE sensor shorted internally causing all sorts of havoc. The person that owned the vehicle had replaced pretty much every 5 volt sensor. tps, map, and several other electronics because it would pop codes for them and he finally got tired of it and replacing sensors 2 or 3 times already. Unplug sensors with a 5 volt reference and a multimeter hooked up on voltage with key on and see if one of the sensors are shorted first. Or if you have easy access to the pcm plug depin the 5 volt reference that feeds those circuits that you see no 5 volts on. Test directly at the pcm instead of guessing.

Tomorrow is my day off so I plan on diving into this mess finally. After putting in a new pcm and bcm (used), I still get the code for A.I.T. sensor (permanently reads -40*) even though I replaced the connector, sensor, and ohmed tested the circut back to pcm connector. After replacing the connector and installing new pcm, I did have the +5v ref @ the end of the connector as well.

Another issue the car has is I cannot get the PCM to engage the A/C clutch. I had a compressor clutch lock up and that grenaded the compressor. So I've replaced/cleaned everything and got it filled by a shop. They said they put in 22 ounces of R134a (even though I requested 24?!?) But since the compressor still wouldn't engage, I wasn't gonna complain at the time. That should have been enough pressure to enable the compressor. I do have a manifold guage set, just don't remember exactly what my static pressure is at the moment. High 80's I think.

At the fuse block, I have 12v's on both sides of my relay. Ground from the compressor is good. All 3 wires going to the high side sensor ohmed out okay as well all the way back to the pcm. And when connected, good voltage on the middle pin.

Is there any way that I can see what pressure my pcm thinks is in the system? Or even like what signal that the other two wires are sending it? I don't have tuning software, but I do have some scanning apps and a bluetooth OBD2 device. I can also connect to the car through a terminal app on my phone, I just don't know how to write the proper command to get the data I want out of it from the AC. I have done it with RPM values, just didn't get any further than that last time I tried.

From my understanding, if everything is "ok" the pcm simply grounds out the circuit upon AC request from the bcm which gets its signal from my HVAC controls.

Sorry my post is so long, just trying to be thorough.

Might have popped the fuse for the compressor. Or melted it. Seen that before on a locked up compressor. Could be cycling switch.