Hi guys! I need some help on a major issue I'm having with my 2005 Grand Prix GXP 5.3L. Let me start off with a bit about myself. 20+ year state certified master mechanic. Ive been around the block more than a few times. This is my personal car and right now, I'm at a loss.

Lets go back about two years ago. One day, I suddenly lost my cruise control, tap shift and my compass now says "CAL". I needed to upgrade the TCM and PCM anyways so I had a custom tuning company flash me performance modules for the car, in hopes it would take care of those issues. I was wrong but the problems weren't that big of a deal. Lets fast forward to last weekend. I was driving along during a country drive and suddenly I noticed my air conditioning went warm. I thought "oh great, just what I need in this heat we have been having". I was less than 1/4 mile from my destination so I just wrote the AC issue off for that moment in time. A couple hours later, I was ready to head home and I remote started my car. It fired for about 5 seconds and shut off. I thought that was odd, its never done that before. I got into the car, and it started with the key. I started to head down the road and it was shifting VERY firmly and my CEL was on. Great, now the trans is in limp mode because of a stored or active engine code. I get it home and put it on the code scanner and it only shows a P0102 ( MAF low voltage). I cleaned the MAF with MAF cleaner, reset the code and tried it again. Same results with a CEL and trans in limp mode. I put on my AC manifold gauges and the pressures were right where they are supposed to be to allow the activation of the AC clutch, but it wasnt activating. I thought maybe my MAF really took a dump and went and picked up a new one. Installed it and disconnected the battery for a couple hours. Hooked the battery back up and took it for a ride. Still no AC, trans still in limp mode and eventually the P0102 code was triggered.

I checked over most engine electrical connections, nothing visually obvious wrong. I'm throwing this out here in hopes to pick someone'* brain for ideas on what the heck could be going on with this car.

Thanks in advance for your help!

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Did the upgrades take care of these "concerns", or are they still a problem 2 years later?

As far as your remote goes, I think when a P code is set, the remote start is disabled......

As far as your a/c goes, you checked hi/lo pressures, and they are above min pressure I assume? Do you have access to a scan tool capable of reading data from the a/c pressure sensor? If yes, does it match your gages? Does your scan tool have the ability to read "B" codes for HVAC?

Have you read MAF data from a scan tool? Checked male/female connections in harness connector to MAF? Flexed harness while watching data?

Have you checked fuses and relays, preferably with a meter?

You mean... Northstar 4.6.

​​​​​​Sorry... I was thinking Bonneville. You're right.

It'* been four months and jusber15 never even responded to our initial input. Guessing he'* not going to be back. Would have been nice to know what fixed his issue.