Which Computer Module is Bad?

[Dammage]

You guys seem to know your stuff and that's very much appreciated. With that in mind, I am having an issue that I am slowly narrowing down. As of now, I think it is a computer problem. My shift indicator does not move in my dash, the speedometer doesn't work, the odometer doesn't work, the ODB II port isn't allowing me to connect my diagnostic tool, the cruise doesn't function, my reverse lights won't turn on, the automatic unlock in park function is inoperable, and the transmission isn't locking into 4th...oh, and my service brake system warning is activated. All of this is still the case after replacing the park/neutral switch, the VSS, the ABS speed sensors, the instrument cluster, and checking all of the fuses. So....riddle me this; is this a computer/control module, and which one is it? If I could get my scan-tool to work, I'd be pretty happy, but if I could get the majority of the other items fixed at the same time, I'd be elated.

Thanks for your future input.

Dammage

 

[808_LS_EXT]

I am only guessing,
as I don't really "know my stuff" with this generation of multiple modules.

All of the problems you listed are powered only when IGNITION is ON? Correct?
If all of those problems arose at once, then I would suspect a fuse, fusible link or circuit breaker has failed.

2¢

 

[The_Roadie]

Hmmm, how much have you read about how flaky grounds can cause almost all of that? Especially the one at the bottom of the radio stack?

Also check front fuse #13.

 

[Dammage]

I ran across a mention of a ground being an issue, but I honestly haven't searched them out because I don't know where to start looking. If I do a search for "grounds" I'm sure I will get a million hits. Is there a map of all of the ground point locations?

I'll recheck fuse #13, but both of my power sockets are working.

 

[The_Roadie]

Good googling is a required life skill. If you get too many hits, add words to the phrase. When you search for "location of grounds", site-restrict the search to gmtnation.com, then hit the images button, I bet you'll cry Eureka!

 

[Dammage]

Okay, so I have checked everything out and nothing has changed. I put star washers on all of the ground connections and rechecked all of my fuses. So, someone told me in another thread that it was my ECM, but I want to know for sure that that is the correct module before ordering it. Can anyone give me any help on troubleshooting which module is bad? I don't want to spend several hundred dollars on computers that are not bad.

Thanks!

 

[Texan]

Did you check the ground connection under the center stack (radio) inside the truck
on the passenger side under the carpet?

 

[Dammage]

Yes I did. It was clean and tight, but I installed a star washer on it anyway.

 

[Dammage]

This is the only thing that I saw that didn't make much sense. Is this post supposed to be empty and why is this wire not connected to anything. This is on the side of the front fuse box.

 

[Dammage]

That red wire is right in front of the naked post and it has a washer connector on it. I consulted the wiring diagrams, but I can't figure out what it is and why it's just sitting there.

 

[Mounce]

That feeds 12v to the trailer wiring harness connector. It comes unhooked from the factory and is only used if you have a battery on your trailer that you want to charge.

 

[Texan]

I think that there is a ground connection underneath the truck, drivers side
on the frame rail not to far from the ABS system.

 

[Dammage]

I haven't checked that one yet, but I'm currently trying to map all of the locations. I've checked 4 so far, but I think I've got a lot more to go. I'll have to wait until this weekend to get the truck back into the garage, but I hope that I'll know all of the locations by then so I can do them all at the same time.

If all of the grounds are good, should I be pretty confident that the ECM is the issue? I don't want to throw good money at a non-issue.

 

[Texan]

I have gone back and reread your original post more than once. Can we get a better history of
how this all came about? Did this all happen at once? Does it run OK? How long have you
had this TB? What is the maintenance history? Just trying to help.

 

[Dammage]

I bought the truck from a dealer who said that the only thing wrong was a speed sensor and plugged catalytic converters. I didn't pay much for it, but this is a bit beyond what I was prepared for. It turns out that the dealer swapped instrument clusters so the mileage is unverifiable, the sensors have all been changed, and I can't get any service history.

I have owned the truck for a month now but I haven't driven it since bringing it home from the dealer. It runs well and the engine seems strong, but I can't establish a connection with my scan-tool to begin to diagnose any specific issues. If I can narrow down the electrical issues, I will be able to determine what mechanical issues are present, if any.

I am pretty good at this stuff, but I'm beginning to regret ever looking at this truck. I'm sure if I can sort this out, I can fix it, but that is starting to seem impossible. Since none of my "treat each issue separately" solutions have fixed anything, I've deduced that it has to be a more central issue. Does that make any sense?

 

[Mounce]

Have you checked the cigar lighter fuse? (I believe #13) It also feeds power to the OBDII port.

 

[Dammage]

Yes, I checked all of the fuses.

 

[Texan]

Are you using a "Bluetooth" connected scanner? In another thread I noticed that you
stated that you had a problem with a ELM327 adaptor. I would hook up a direct
connected scanner before I bought a new ECM. Just a suggestion.

 

[Dammage]

It is a bluetooth scanner, but since it works in my other vehicles, I just discounted the fact that it could be my scanner. I will take it down the street and see if one of the parts stores will hook up a hard-line scanner to it. Thank you for the suggestion.

 

[Dammage]

So, I haven't found any bad grounds. I also haven't replaced the ignition switch yet (because I have just been too busy the last week or so). I had my dad bring his Tech II scanner up, and even though we get power to the ODB port, there is no info. SO....where do you all suggest to go to get a new ECM? I haven't seen any obvious options in my search so far but I imagine that there has got to be one somewhere.

Thanks!

 

[bassman]

Its been a while and I don't know if you found your problem yet. Do not unplug engine computer from your body computer as it won't start. You can unplug any seat modules or door modules one at a time and if it corrects your problem, you have located the area where your problem originates.

 

[Dammage]

Thanks for the advice. I will try disconnecting individual modules and see if I can narrow it down. I haven't driven the truck in many months and would like to get it on the road. As it's getting nicer out, I'm going to be picking back up on my troubleshooting.

Thanks again!