John Tyra

1988 Chevrolet 2500 Pickup - Scanner Won’t communicate - Paperclip Won’t work & Much More



1988 Chevrolet 2500 pickup with 350 engine, TBI and OBD1. I bought the truck in 1990 with 21,000 miles on it. It is now up to 280,000. Within the last 3 years most of the sensors and connectors have been replaced. A new distributor and coil was put on about a year ago. Fuel pump and filter is brand new and the fuel pressure is right at 12 lbs. Installation of the pump was prompted by poor engine performance and low fuel pressure. Pump was very old and had a break in the suction tube. Engine performance was restored.



For several years I have used a Actron 9145 scanner to trace minor problems and make repairs. About a months ago I had what I thought was a check engine light come on. I discovered that the Actron would not communicate with the ECM and showed I had a Link Error or something similar. I attempted to read the codes the old fashioned way with a paper clip jumper and had negative results. The engine seemed to be running fine and I disconnected the battery and cleared the codes. After a three mile drive, I parked the truck and tried to use the Actron again to look for codes or read data. I could not communicate but the check engine light was not on indicating a problem. Later in the day, I started the truck and the Check Engine Light came on. I turned the engine off and came inside to do some auto repair research on the internet. After about 45 minutes I went out and started the truck and I did not have a Check Engine Light. Again I went for a short drive and everything remained normal and I I did not have a Check Engine Light . Tried to scan and could not communicate. After about 30 minutes I started the truck and had the Check Engine Light back. Tried to scan and could not communicate. After 20 minutes I found that the Check Engine Light had cleared.







Recap of above paragraph:



Had Check Engine Light

Actron 9145 would not communicate with the ECM

Paper clip method would not work either

Went for a drive and parked with Check Engine Light (CEL) still showing

Disconnected the battery and cleared the codes

Went for 3 mile drive…..no CEL…..running fine.

Tried to use the Actron 9145…..could not communicate but the CEL was not on indicating a problem

Later in the day, I started the truck and the CEL came on

After 45 minutes, started truck and CEL had gone off

Short drive…running fine….No CEL

Tried to scan and could not communicate

After about 30 minutes…. Started the truck and CEL was back

Tried to scan and could not communicate

After 20 minutes, started truck and the CEL had cleared

I have ALLDATAdty and ran the GM flow charts to check for missing voltage, broken cables and bad connections between ALDA connector and ECM. My problem does not completely match any of the ALLDATA chains of testing but ran with their thinking in hopes I would stumble into the problem. Didn’t happen. Your help would be appreciated.

Sabino56

I guess I’d focus on making sure the ECM is alive and well first. If you can’t get it to flash codes with a paper clip that’s the place to start.
If I had what you described the first question I’d try to answer is whether the ALDL connector is solid. Look at the connector, make sure the contacts look ok, none are bent up, etc. if nothing obvious on connector or wires into connector - then it’s to the ECM to check. I assume the ECM is behind the glove box like on my 93. You’ll need to find the ECM # and then the pin out for the connectors on the ECM and do the paper clip test there. You can Check on GM ECM - Bins - TunerPro Definition Files - Wiring Diagrams - Tuner Info! for info. Maybe someone there has better suggestions on how to verify an ECM is working ok.

good luck

John Tyra

I have been on the road and just got back in to read your post. I agree with you that it is possibly the ECM. I just want to feel stronger about it before ordering a $100.00 item. The webpage you recomended looks good. I am waiting to be approved in order to dig in deeper. Thank you.

John Tyra

I think I am on a trail. The ECM container box heats up and that is when it fails to communicate....no data and will not give code 12 or any other codes. I cool the box down with a high speed fan and I get my CMU back,,,,it works. Have you ever heard of this? Is it a sensor with a problem causeing this or is it just a bad CMU?. I guess it could also be a short somewhere but I can't find one.

I still haven't been approved onb the site you told me about. I have done some research there.

Sabino....... I grew up 20 miles from Sabinal, Texas.

Sabino56

It makes sense to me that if the ECM is getting too hot it will fail, fail to communicate. I don’t know what a CMU is?
regardless, I wouldn’t think a sensor input would cause the ECM to overheat. There are some drivers in there that may but I’m way out of my league on debugging an ECM. The guys on gearhead-efi would be place to ask.
Sabino is from a canyon in Tucson, Az, though ok grew up in Houston.

John Tyra

When I say CMU, I am trying to say ECM. My brain and fingers don't communicate very well.

I think I am approved to move around Gearhead now. It will be interesting to see what I find out.

Thanks for your help. I will let you know the final outcome.

John Tyra

When I say CMU, I am trying to say ECM. My brain and fingers don't communicate very well.

I think I am approved to move around Gearhead now. It will be interesting to see what I find out.

Thanks for your help. I will let you know the final outcome.

Sabino56

I was told that when electronics fail 98% of the time it’s a bad capacitor or bad solder joint. If you end up pulling out and opening ECM you can look for anything obvious (ie something that looks fried). If you go route of replacing ECM my understanding is you need same ECM pn and bin (code). You can’t just replace with any ECM. Again those guys on gearhead would be best for advice. They seem to be more into tuning than troubleshooting so may have to be patient. Good luck

John Tyra

Thanks. I really appreciate your help.