442 Eprom issue

JAMES L EUBANK

JAMES L EUBANK

Apprentice
Feb 18, 2018
55
18
CLARKSBURG, WV
So, I am looking at a car for sale. I ran the obd scan and it came up with code 51. But, it ran fine down the road. I cleared the code, but it came up again. Code 51 is an eprom issue, but how could it run fine with an eprom issue? Not sure if this is a major issue or not. Has anyone ran into this issue? Problem is on a 1985 Olds 442.
 
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69hurstolds

69hurstolds

Comic Book Super Hero
Supporting Member
Jan 2, 2006
3,886
113
Is it stock? Or supposed to be? Code 51 is a prom error. Could be from reading it wrong, or damaged prom or ECM itself. But if it's running great, then it's probably just getting an incorrect checksum error. Which in and of itself wouldn't do anything performancewise, but it would set the code and you'd get a CEL. Clearing it won't matter as it would come back likely the next time you ran the car afterwards.

Does it have an aftermarket PROM? I've heard of Hypertechs doing this. Not always, but sometimes. Also, if it's not the correct PROM compatible with the ECM firmware, it could cause the code.

Your ECM box should be a 16047963 production, and 1226457 service number. And the PROM for an 85 442 should be an 7987FCH code prom with service replacement number of 16047986.

It would take some digging into to find out exactly why it's doing what it's doing, but if you're wanting to buy it, you can use the fact that's it's throwing a code that won't go away to leverage a discount.

Save a few hundred, then buy this for 75 bucks and replace all that crap at once. :)

https://rover.ebay.com/rover/1/711-...0001&campid=5335822911&icep_item=173367058240

If you can access the ECM...

It should have a big FCH on the label, and if it's a GM PROM, it should have an FCH on it somewhere.


FCH 85 VIN 9 chip boxes.JPG


FCH 85 VIN 9 chip.JPG
 
JAMES L EUBANK

JAMES L EUBANK

Apprentice
Feb 18, 2018
55
18
CLARKSBURG, WV
Is it stock? Or supposed to be? Code 51 is a prom error. Could be from reading it wrong, or damaged prom or ECM itself. But if it's running great, then it's probably just getting an incorrect checksum error. Which in and of itself wouldn't do anything performancewise, but it would set the code and you'd get a CEL. Clearing it won't matter as it would come back likely the next time you ran the car afterwards.

Does it have an aftermarket PROM? I've heard of Hypertechs doing this. Not always, but sometimes. Also, if it's not the correct PROM compatible with the ECM firmware, it could cause the code.

Your ECM box should be a 16047963 production, and 1226457 service number. And the PROM for an 85 442 should be an 7987FCH code prom with service replacement number of 16047986.

It would take some digging into to find out exactly why it's doing what it's doing, but if you're wanting to buy it, you can use the fact that's it's throwing a code that won't go away to leverage a discount.

Save a few hundred, then buy this for 75 bucks and replace all that crap at once. :)

https://rover.ebay.com/rover/1/711-...0001&campid=5335822911&icep_item=173367058240

If you can access the ECM...

It should have a big FCH on the label, and if it's a GM PROM, it should have an FCH on it somewhere.


View attachment 146269

View attachment 146270
Seller cant tell me much on original parts or not. He says he didnt replace it since he has had it. Hes offering $500 off due to the code. Sounds like if I change the eprom out, then the major culprit for this code is removed. Is there a chance of complete shutdown if the car is driven before the eprom is replaced? Should I trailer it if I buy it? It would be a 70 mile drive home and I was hoping to save on trailer rental.
 
motorheadmike

motorheadmike

Geezer
Nov 18, 2009
5,102
113
Ottawa, Ontario Canada
Tell him to make it a grand and you got a deal.
At least - especially if the plan is to keep it OEM.

Have fun finding spares without robbing 69hurstolds house.
 
airboatgreg

airboatgreg

Royal Smart Person
Oct 2, 2016
1,916
113
EProm is the Erasable Programable Read Only Memory that is built into the ECM. It normally expires at about 15k miles so I suspect the PROM needs to be updated, an aftermarket as mentioned above or an ECM issue.
 
69hurstolds

69hurstolds

Comic Book Super Hero
Supporting Member
Jan 2, 2006
3,886
113
How long did you drive it around? If you drove it around for a good bit and nothing bad happened, I'll bet you can easily make it home.

Also, if it was messing up, it likely would have gone into limp home mode, and although run like crap, it would still go. If that's the only issue is the check engine light, the prom either works or it does not. If it runs great then I would suspect there's something amiss with the prom or ecm.

There shouldn't be an "eprom" in that car. Only a PROM. If someone jammed something else in there, then I dunno what you got.

Likely the Prom is messed up if anything. The ECM boxes are pretty durable for the most part. Not saying you can't toast them, but if you did, I suspect the car wouldn't run worth a flip and have several other trouble codes lock in.

Just my advice.
 
JAMES L EUBANK

JAMES L EUBANK

Apprentice
Feb 18, 2018
55
18
CLARKSBURG, WV
How long did you drive it around? If you drove it around for a good bit and nothing bad happened, I'll bet you can easily make it home.

Also, if it was messing up, it likely would have gone into limp home mode, and although run like crap, it would still go. If that's the only issue is the check engine light, the prom either works or it does not. If it runs great then I would suspect there's something amiss with the prom or ecm.

There shouldn't be an "eprom" in that car. Only a PROM. If someone jammed something else in there, then I dunno what you got.

Likely the Prom is messed up if anything. The ECM boxes are pretty durable for the most part. Not saying you can't toast them, but if you did, I suspect the car wouldn't run worth a flip and have several other trouble codes lock in.

Just my advice.
I test drove it for 10 miles and mor on city, county, and interstate roads and ran without a hiccup. The code 51 worried me because I have never ran into that code before. Thanks for the advice. I will keep it in mind.
 
airboatgreg

airboatgreg

Royal Smart Person
Oct 2, 2016
1,916
113
Eprom's are hard wired in to the ECM and not replaceable. If it were mine I would gingerly connect and re-connect the ECM a couple of times. Check engine and body grounds. Do you have a stereo amp near the ECM? If so, could cause some electrical interference
 

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