Code 51 help?
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Code 51 help?
Hi guys, so as some of you may know I've been having an idle surge problem and a lean hesitation in open loop when you rev the engine, the engine bogs down and then kicks up.
So I've tried pretty much everything I could think of to diagnosis to no avail, so I downloaded tuner pro rt to see if it could give me some insight.
My car is mildy modified, and the computer is tuned and had an adapter soldered in.
This is a 1985 corvette by the way.
Anyway, I got tuner pro rt up and running, and I noticed that two Check Engine Light Codes were picked up by it, this is data logging in diagnostic mode with the a + b terminals shorted.
The two codes were code 22 for TPS voltage low, which can't be because I had just adjusted the TPS today and tuner pro rt was reading .55v at idle, so it definitely isn't low, and code 51, which as I understand is for a problem with PROM or a faulty memcal or something?
So my question is, what is the diagnostic for it? What are the possibilities? Is this normal during diagnostic mode? What is a memcal? Etc. Etc.
Thanks a lot!
So I've tried pretty much everything I could think of to diagnosis to no avail, so I downloaded tuner pro rt to see if it could give me some insight.
My car is mildy modified, and the computer is tuned and had an adapter soldered in.
This is a 1985 corvette by the way.
Anyway, I got tuner pro rt up and running, and I noticed that two Check Engine Light Codes were picked up by it, this is data logging in diagnostic mode with the a + b terminals shorted.
The two codes were code 22 for TPS voltage low, which can't be because I had just adjusted the TPS today and tuner pro rt was reading .55v at idle, so it definitely isn't low, and code 51, which as I understand is for a problem with PROM or a faulty memcal or something?
So my question is, what is the diagnostic for it? What are the possibilities? Is this normal during diagnostic mode? What is a memcal? Etc. Etc.
Thanks a lot!
Thread Starter
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I have never seen this code before, only when I opened up Tuner Pro RT instead of Win ALDL.
Maybe I'll ask in the Scan & Tune forum.
Not sure if it's supposed to show that code during data logging or not, pretty sure it's not supposed to.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
When the ignition is first turned on the ECM does a checksum test. If it fails the test it sets error code 51.
The checksum is done by adding all the bytes in the data section of the EPROM and comparing the result to two numbers stored in the EPROM. If the numbers don't match you get a code 51. This doesn't affect the operation of the car at all. This is a result of modifying the contents of the EPROM. There are programs available that will calculate the correct checksum and then it can be stored in place of the stock checksum result.
There is also a checksum workaround. Supposedly, if you store the value $AA in the first byte of the checksum the ECM will skip the checksum test. I say supposedly, because I have done this and still got a checksum error.
The checksum is done by adding all the bytes in the data section of the EPROM and comparing the result to two numbers stored in the EPROM. If the numbers don't match you get a code 51. This doesn't affect the operation of the car at all. This is a result of modifying the contents of the EPROM. There are programs available that will calculate the correct checksum and then it can be stored in place of the stock checksum result.
There is also a checksum workaround. Supposedly, if you store the value $AA in the first byte of the checksum the ECM will skip the checksum test. I say supposedly, because I have done this and still got a checksum error.
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Safety Car
Joined: Nov 2009
Posts: 3,973
Likes: 341
From: Adelaide South Australia
I had a code 51 and it was a bent tang on the computer chip, have you taken the chip out and checked that all the small internal tangs on the chip are straight ?
(you need good eyes and light for that one !)
(you need good eyes and light for that one !)