03 TB, 29 trouble codes, most are communication codes

[jheltze3]

I have a 2003 Chevy TrailBlazer with 84,000 miles on it. I bought it from a used car dealer 2 months ago. Changed O2 sensor, battery, and cleaned the throttle body.

Last night the check engine light came on. This morning I took it to Autozone and they read off 29 trouble codes. I was told there were ABS codes and about 25 of the codes were communication codes.

The technician said it was possible the ECU needed to be flashed and I could take it to the Chevy dealer to see if they could do that.

Does anyone have any information on this type of issue? Are there any recalls on this vehicle dealing with this issue?

Any help would be great!

Thanks,
Josh

 

[The_Roadie]

Welcome! Glad you found us.

29 codes is an extraordinary number! I have to guess most of them are "pending" or historical codes in memory, not actively the cause of the CEL. If there's any way you have access to a code reader that can give you a list that's separated by urgency level, that would help a lot.

There is no generic recall or TSB for general communication failures. A problem communicating to the ABS module will typically light up the ABS/brake warning lamp, not the CEL, which is mostly reserved for engine issues. There are definitely updates for the PCM available at the dealer, but most of them are for specific issues you may or may not be having. Like improved performance for the fan clutch in hot weather, cruise control surging when descending slight grades, etc. The dealer could also do a proper diagnosis of the immediate root cause of the CEL, but so could any competent independent mechanic. Most of us on enthusiast forums are fans of independent mechanics for things we can't do ourselves. Dealers can be stellar or not. The worst ones take your money, don't fix the real problem, and don't guarantee they have the diagnosis right the first time. Independents with poor reviews can do the same. You gotta be careful.

For $50 you can buy your own code reader, and I recommend one person in EVERY group of friends or neighborhood has one. You could buy one and then charge a six-pack to use it on your buddy's vehicles, and pay it off in a short time. If you get a better place than a parts store to read your codes, you will get a better sense of the priority you need to assign to fixing the issues.

Does your ABS work on a sandy or gravel road, for instance? If it does, then you can defer doing anything about ABS codes.

 

[jheltze3]

I believe they said all of them were history codes and that nothing was active. They didn't seem to think there was anything I could do other than call the dealer. If they update the PCM, does that mean they flash it?

 

[The_Roadie]

Autozone = Fail. There would not be a CEL lit up without an active, current code. You need to find a code reader more competent than the non-mechanics at the parts store. Then tell us what the code is that's causing the CEL to be on.

Yes, the dealer's process to update the PCM is called a reflash. I doubt you need it.

Any independent mechanic will have a decent code reader, but they'll charge you as much to read the code once as it will cost you to buy your own. And then you have it forever. Check your buddies for recommendations, or my favorite for honest (mostly) reviews is yelp.com.

Do you have anything obvious wrong like the temp gauge is not sitting straight up at 210 degrees?

 

[CaptainXL]

Last night the check engine light came on. This morning I took it to Autozone and they read off 29 trouble codes.

Ok. What are the codes?

 

[jheltze3]

Sorry for the long wait. Hope no one was on the edge of their seat, lol.

Yes, Autozone did nothing to help the problem. The Chevy dealer set me straight, after I paid more than I would like for a diagnosis.

1. Do not unhook the battery to erase codes. This may cause other codes, such as the communication codes Autozone saw and assumed it was my PCM. It may also damage the PCM. Definitely an important lesson in their somewhere.

2. The only active code was a low coolant temp sensor, P0128. I had seen this before and ignored it when the MIL went away. It was later explained to me that my engine runs around 175, instead of the recommended 210. I knew this, but thought nothing of it. After all, it's not overheating. However, running to cold is not good for the engine either, as engine oil viscosity is a function of temperature.

I assume a lot of you I6 engine owners known this, but changing the thermostat is not an easy job. I did it, and do not plan to deal with thermostat/alternator issues myself for awhile. The old thermostat appeared to have been stuck open. I put a new one in. Guess what... engine temp runs right at 210 when warmed up.