I just bought a 2004 Monte SS supercharged. Originally my friend bought it about a month ago and we fixed the fuel injector and he posted about it smoking. The smoke cleared up after a good drive. I dont know the history of the car but it is throwing a ton of codes and check engine light is on air bag light is on Abs light is on brake light is on sometimes traction control light is on. Codes are b1000, u1000, u1040, p0171, intermittent u1064, intermittent p0856, intermittent p1626, intermittent p0420, intermittent u1096, intermittent b007. Car doesnt apear to have ever been in an accident . There was an after market radio spliced in with a harness connector with the wires just twisted togeather and not even taped and it didn't work. #1 fuel injector was stuck open and I traced that to a spot the k&n filter was rubbing the wire harness shorting the fuel injector wire to ground. I repaired that and the engine runs good now but long term fuel trims are 16.4. The car seems to run and drive good after fixing the fuel injector wire and I got it cheap or I wouldn't have bought it. With so many codes I'm not sure where to start though. What are the chances these codes started one by one and the previous owner let them go? Or do I have a bad pcm or bad ground or some other electrical problem causing the bulk of them?

 

I just did a search for some of your descriptions and found this that might be worth the look over.


https://www.google.com/search?q=2004...w=1389&bih=680

 

Ok so I'm pretty sure the p0171 lean code is a vacuum leak. I just have to find where its at. The fuel trims are real high at idle. If I give it some gas the short term trim drops immeiately and the long term drops pretty quickly until my fuel trims are in the normal range. Drop it to idle and they shoot back up again. As far as the other codes I checked somewhat for voltage drop and bad ground. I get no drop from the battery to various points on the engine, the body, the firewall, the body of the pcm, or the cigarette lighter. Resistance from the battery negative to the same points is only about 0.3 ohms. The battery was only at about 12.4 volts though despite driving it for the past few days. It' charging at about 14.6 volts. If the engine is not running even small loads make the voltage from the battery drop significantly lower. If I start the engine like 3 times and shut it off the battery is down to 12 volts. I think the battery is bad. The car starts no problem though. I'm going to replace the battery and see if that helps.

 

You might want to have the Alternator checked too. Sometimes when they go bad they take the battery out as well.

 

The alternator seems ok. I changed the battery and checked the connector to the EBCM. I unplugged it and plugged it back in a few times. Then I cleaned the ground to the EBCM. After that the u1040 for the EBCM and the brake light on the dash were now going out and coming back on every now and then, then going out again. I couldn't get that light to go out or code to disappear before. I looked over the wiring harness for damage and didnt see any. I then cleaned the ground to the body right near the battery and noticed no change. I then disconnected the battery again and one by one pulled every fuse having anything to do with the computer systems with the car and cleaned them. After I did that I started the car and the lights for abs, traction, and brake are now off. I scanned it and am still getting the u1040 code though and am still getting b0077, b0080 or b1000 for driver side and left side impact sensor and I believe air bag module. The air bag light is still on. It also threw the p0171 after driving for a bit which I'm pretty sure is a vacuum leak or maby an exhaust leak. But it is weird it didn't throw the check engine light. It didn't throw the brake light either for the u1040. When I key on and start they all light up for the test and go out except the air bag light stays on and the abs light doesn't come on at all. I hope I didn't mess something up. I want to try cleaning the rest of the grounds. I' m going to clean positive cables too. Where do the other main grounds from the the battery go and where does the airbag module ground? Any ideas what else to look at for electrical gremlins?

 

Abs, brake light and check engine came back on.

 

Could be a failing BCM for some of the codes... Fairly common in that generation of Montes IIRC.

 

The only code having to do with the bcm was the u1064 which hasn't come back since I first made this thread. All the stuff the bcm controls such as lights etc are working fine and my scanner has no problem communicating with the bcm which shows no codes.

The codes that almost allways are on are as follows.

U1040 - lost communications with EBCM

B0077 OR B0080 OR B1000 - air bag sensor codes or electronic control unit malfunction

P0171 - lean condition. My fuel trims are realy high at idle. I checked visualy and with tb cleaner for vacuum leaks and didn't find any. I do have an exhaust leak from the downpipe/cat area so maybe that's it.

P0856 - traction control input signal. This one is not on all the time but comes and goes regularly.

Also I was unable to scan for abs codes before but I noticed when the u1040 code and brake light disappear momentarily I was able to scan abs codes and got a c1234 tried to clear it and u1040 came back and I lost communications with abs and my scanner. I highly doubt bcm is the problem. I'm leaning more toward a bad ebcm and air bag module or bad pcm or maybe bad ignition switch or bad wiring but I have been unable to find a wiring problem that fixed any issues. I did also clean the ground under the pcm. Battery holds a good charge of about 12.8 now and alternator outputs about 14.2 or so. I may replace the pcm with a zzp one anyways and get a performance boost and 180 fan turn on temps and maybe fix my problems too. I could do the zzp downpipe too and fix my exhaust leak. I don't have the extra cash for all that at the moment though, got bills to pay. How can I properly trouble shoot these codes without just throwing parts at it.

 

It appears I am having trouble communicating with the ebcm. I got a copy of gm techline esi factory service manuals. After spending some time reviewing it. I found the troubleshooting diagnostic procedure and connector pinouts to properly and thoroughly test the wiring to the ebcm and all other modules communicating on the class II bus with the ability to isolate each module via the splice pack near the bcm. If the wiring checks out to the ebcm with it isolated and I still have no communication to the ebcm then it is bad. Im still suspecting I will find a wiring problem though. I might not have the chance to test this right away but when I do I will update the thread and let everyone know what I find.

 

I tested the wiring to the ebcm. I didn't find any problems with the class ii data wire or positive power wires. The two ground wires show a resistance in the thousands of ohms range though. I was able to scan the ebcm again while the light went out one time and it showed history codes as follows.

c1236 - low system supply voltage
c1248 - ebcm turned on brake warning indicator
c1254 - abnormal shutdown detected
C1277 - torque signal circuit malfunction
c1298 - class ii data malfunction
u1000
and a current c1234 - left rear speed sensor

It seems the problem is I still have a bad ground along with a bad harness to one speed sensor. I'm going to try cleaning the grounds again and this time I will sand the body where they go on instead of just using a wire brush. I believe the ground for it is the one under the pcm and the other one kinda near it I think grounds the actual abs pump. Someone chime in if they know another ground location for the ebcm.

As far as the p0171, I have a zzp 3" catted downpipe on order along with new o2 sensors which are probably ok but the car has 156000 miles and i doubt if they have ever been changed. I also have a new maf on order the generic reman one on the car is definitely suspect and it seems like it might not be calibrated right. Either way I can't trust it