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Username Post: 88 Chevy 1500 ECU issues?        (Topic#366694)
Derpenstein69 
Newbie
Posts: 5

Age: 32
Loc: CA
Reg: 10-13-21
10-13-21 03:14 PM - Post#2829107    

so i get up to take my truck to smog, decide to check codes before i waste my time (check engine light doesnt work). DTC 31,32,33,35,42,43,51,52,5 4,55 show up. this seems similar to something that happened to me about two years ago, replaced ECM, fixed all the problems and codes went away 2 years ago. so i assume since its throwing ECM and related codes, thats likely the issue this time again. replace ECU again, yes i am certain i got the right ECU. put in the new ECU and get codes 12,14,23,25,34,35,41,42,4 3,51 immediately on first startup. run it for a couple minutes on what im assuming is limp home mode, smells to be running rich and idling high. recheck the codes now i have 13,25,34,35,42,43,51,54,5 5. i did put the calpack and prom chip into the new ecu correctly (they only fit one way by design they cant be put in backwards) took out the chips checked the connections and replaced them again, left battery unhooked to clear codes and tried again. after reset im getting codes 12,13,14,23,25,33,34,35,4 2,43,51,54,55. i had read on some of these forums that it could be a grounding issue, so i ran a wire from negative battery terminal to the housing of the unit just to be able to test and be certain it wasnt a bad ground with no change in the DTC codes. I'm really not sure what to check or try next i hoped that replacing the ECU would fix it again but no such luck this time around. any tips, tricks, advice, or things to try is most welcome, im not sure how to proceed from here.
edit: 1227747 ECM (replaces 777747) purchased remanufactured Cardone ECU from O'Riellys



 
thx1138v2 
Contributor
Posts: 246

Reg: 05-01-14
10-14-21 12:29 PM - Post#2829162    
    In response to Derpenstein69

If that is all correct your are getting conflicting ODB1 codes. Code 12 means "System normal" which means you shouldn't be getting any of the other codes.

Have you driven it around for 1/2 hour or so after resetting everything? If not, do so and check again. When driving around do some normal "city" stop and go and then put some hiway miles on it.



Edited by thx1138v2 on 10-14-21 12:29 PM. Reason for edit: No reason given.

 
Derpenstein69 
Newbie
Posts: 5

Age: 32
Loc: CA
Reg: 10-13-21
10-14-21 01:31 PM - Post#2829166    
    In response to thx1138v2

yes the conflicting codes i am assuming are from the faulty ECU, as a similar thing happened with a bunch of unrelated codes all variations of the computer is reading a signal that seems wrong the last time i had to replace the ECU about two years ago. Each code has something to do with the computer reading a signal however so that leads me to believe the majority of the codes are being thrown due to a fault in my ECU or a wiring issue possibly?. i have not driven it but i will try that today with the new ECU and see what happens. i am aware that i should find out WHY my truck has thrown two ECU's in the past two years, my most likely culprits are the aftermarket security and radio that was installed by the previous owner. the last time i changed ECU the codes were gone immediately it was fixed without driving, but i will still try that to see if it works. is it possible i just got a bad remanufactured PSU from the auto store? some other threads i was reading on here where someone had to try a few different remans before finding a working one. im not going to mess anything up too bad driving it around for a half hour on limp home mode with it idling high and running rich?

edit: reading through another thread there was someone suggesting that the check engine light was due to bad computer and they had someone put a 9v battery to a certain pin on the wiring harness to see if the 9v battery illuminated the light when the psu wasnt? my check engine light is not working, im not sure how long it has been that way i seem to remember it used to work, but throwing codes without a check engine light is that possibly relevant?



Edited by Derpenstein69 on 10-14-21 01:35 PM. Reason for edit: No reason given.

 
someotherguy 
Senior Moderator
Posts: 29480
someotherguy
Loc: Texas
Reg: 08-01-03
10-14-21 02:59 PM - Post#2829170    
    In response to Derpenstein69

When you turn the key on, prior to starting the truck, a lot of your dash indicator lights should come on. This is the 'bulb test' - and the check engine light should be one of them. Most likely reason for no CEL function is the bulb is simply burned out. Easy to replace.. start there.

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
Derpenstein69 
Newbie
Posts: 5

Age: 32
Loc: CA
Reg: 10-13-21
10-14-21 03:13 PM - Post#2829171    
    In response to someotherguy

ya the check engine doesnt come on at start with the other lights, ill check the bulb. i will drive it for a half hour or so and try that and report back.



 
thx1138v2 
Contributor
Posts: 246

Reg: 05-01-14
10-14-21 04:32 PM - Post#2829174    
    In response to Derpenstein69

I'm not at all familiar with the '88 1500 but you should also check where the wiring harness leads to the sensors being reported go through the firewall. There might also be connectors going through the firewall at various places rather than wires. They would need a continuity check also.



 
Derpenstein69 
Newbie
Posts: 5

Age: 32
Loc: CA
Reg: 10-13-21
10-14-21 05:12 PM - Post#2829177    
    In response to thx1138v2

drove the truck for 45 minutes, no changes in the codes being thrown, it was worth a try. i have a multimeter and code scanner and know the basics of how to use them, how does one go about checking to make sure its the pcu not the input wires? continuity check on the wiring harness is something i have seen mentioned in other related threads on this site but dont really know how to do. i assume im looking at a specific wire for a specific measurement on the multimeter?




 
thx1138v2 
Contributor
Posts: 246

Reg: 05-01-14
10-15-21 02:51 AM - Post#2829197    
    In response to Derpenstein69

A continuity check just checks whether or not a wire is continuous, i.e. has no breaks or shorts.

You have to locate both ends of the wire. Then set your meter to ohms and put a probe on each end. If it reads zero or just a few ohms there is no break in the wire. If it doesn't give a reading then there IS a break in the wire.

Most meters these days have a setting that does this and indicates continuity with a tone.





 
65_Impala 
Very Senior Member
Posts: 4818

Reg: 12-29-02
10-15-21 06:10 AM - Post#2829205    
    In response to Derpenstein69

The ECM's don't fail to limp mode very often. They don't output codes when that happens either.

Take the ground off the ECM case if you haven't, that is a quick way to burn-up an ECM. Only ever ground the ground wires to the engine and keep the case floating.

You sure you're reading the codes correctly? You've got codes that don't apply to that ECM, 23 & 25 don't apply, that ECM doesn't use an intake air temp sensor.

Start checking the power and ground wires to the ECM.

Check the charging voltage to ensure it is correct. 53 = High battery voltage is odd to see.

12 isn't a "system normal" code. It is a code saying no reference pulses are received from the distributor. It will be set when you turn the key on and the engine isn't cranking. It would stay off if you cleared the codes while the engine is running but would come back on the next start.

Here's a good source of info.

http://gearhead-efi.com/Fuel-Injection/showth read....





 
Derpenstein69 
Newbie
Posts: 5

Age: 32
Loc: CA
Reg: 10-13-21
10-15-21 11:29 AM - Post#2829216    
    In response to 65_Impala

If a failed ECM wont put out codes, well there goes my best guess! i know its rare but possibly the prom actually is the issue? i dont know for a fact it is in limp home mode, im not sure how to verify that, i know its idling high and running rich and that made me think it was in the limp home mode. i am using an obd1 code reader with the chevy attachment that lists the codes on my reader, it has been a good machine that i have used for this truck before, not doing the jumper wire and watching blinking light method, so the codes couldnt be me misinterpreting the blinks at least.

Based on the feedback i intend to do a continuity check on the wiring harness on some of those sensors that say they arent reading properly, and check the power and ground wires to the ECM using those diagrams that were linked, and ill check the engine charging voltage. im not sure how to clear codes with the engine running, since the only way i am aware is to disconnect power, is there another way i am missing? (my code reader wont clear the obd1 codes)

i will update you all when i have done the suggested things, i really appreciate all the help. i love this truck a lot more than its value and want to keep it for my son someday, whatever it needs im gonna try to make it work.

edit: waiting to be approved on that other forum to be able to see the diagrams, also i had removed the ground from the case to the battery right after i had tested to see if that was the issue, didnt know it could be a problem but since my ECU is still throwing codes i think from what i have read that means i fortunately didnt fry it

Edit 2: finally approved for the other forum with the wiring diagrams, will find time this week to do the recommended testing now that i have access to that information and post here again when i have have more info from that.



Edited by Derpenstein69 on 10-19-21 12:07 PM. Reason for edit: No reason given.

 
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