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OK, here's a weird one for you. I have a 2002 Z28 with 140k+ miles and original everything. It needed new cats cause it was throwing the codes for them. I figured while I was at it, I put in a new clutch.

Getting the old CATS off was a nightmare and I was sure I'd rip the bolts off the exhaust manifold in the process, so I decided to unbolt the exhaust manifolds from the heads and take out the CATS that way. This allowed me to use a torch on the rusted bolts and remove the CATS without destroying the manifold bolts.

The passenger side manifold came off with no issues, other than it was a bitch trying to get my hands in there to unbolt it. The driver side was another story. The first bolt (front of engine) snapped off the head and left about half an inch sticking out that I could grab and unscrew. I wasn't so lucky with the last bolt closest to the firewall. It snapped off flush with the head. So, now I had to take the head off to drill out the bolt hole and re-tap it with a heli-coil. Of course this meant taking off the manifold and everything else that goes with it.

Okay, so here comes the problem. I get everything back together again and all works fine, engine starts right up, clutch works great. No indication of rough idle or vacuum leak of any kind, except now out of nowhere I get a P0107 code (MAP sensor) and a C0240 code saying that the ABS is inoperative. BTW, the check engine light is operative, but it's not on. I only know there is an issue because my scanner says so. A coupe of times I was able to clear the codes for about a minute or two, then they came back. I checked the voltage for 5VDC on the MAP sensor connector and it's fine. I replaced the MAP sensor, still the code won't clear.

Just so you know, I disconnected the battery before I started and it stayed that way for about a month. When I finally finished the work and reconnected the battery, the PCM started throwing these codes. Oh, yeah, the original codes I had related to the CATS are gone now as I replaced the CATS and the 4 Oxygen sensors. The car runs fine, so I doubt there is a vacuum leak. I've tried clearing the codes, but they just come right back again and I'm sure that I haven't shorted any wires, so I'm thinking that maybe the PCM went bad after being dead for a month or so?

Ever heard of that happening?

Thanks for any advice.
 

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Pcm's in these cars rarely go bad. The code for the map indicates low voltage. Since work was done to engine, I would check for any grounds that might have been disturbed. This includes the pcm grounds.

We have a 2000 factory service manual in the 4th gen section to get wiring diagrams and such from. Look for thread titled "GM service manuals".

Map has 2 ground circuits from pcm. Connector A and B.

I would think ABS code might be related to other code, but check your high mounted brake light for operation, as it being out can mess with ABS.
 

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here's a link to some info and a video on the MAP failure, it's not an LS1 but s/b similiar.. What I don't like in the video is he uses a chassis ground to test when he s/b using the ground wire to the MAP in the connector. Basically he's testing the MAP +5 supply and sensor operation but not the complete circuit (ground) from PCM . If you had an open ground wire from the PCM his test would work.. MAP Sensor (Manifold Absolute Pressure) Description
 
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