I have a 98 Eldo that registers some history codes when I run them, but my mechanic put hooked his diagnostic computer up and nothing showed for codes on his computer?
Is this due to them being "history" codes?
I don't have any issues with my Eldo running, no service engine light, nothing appears to be an issue. I am just concened about the "history" codes. Maybe I shouldn't be??? I wrote them down to just keep an eye on things, but I was a bit confused when nothing showed on the mechanics computer?? Anyone familiar with this type of thing?

If it's in history...don't worry about it. It just means that the PCM recorded a fault at one point in time, and kept a record of it. As long as there's no current faults, then there's nothing to worry about.

Yeah, don't sweat history codes. Clear 'em and see if they return. Out of curiosity, what where they?

Thanks guys, i have been told "history" codes are nothing to worry about if there is no current issues, but being a novice and learning I need to hear a few times to really be confident they aren't an issue.
I will post the codes tomorrow, I have them at home. Back to work, again, thanks.

Some codes are proprietary, non emissions codes. Not all computers will display them. Which ones did not show up?

It doesn't matter if they are history or not. It has more to do with the list in the computer matching the codes in the car.

Many U, B and C codes won't turn up when looking in the PCM as an example.
You may have several codes that start with those letters, perhaps he was checking the engine computer but the codes were in one of the dozen or so other computers on the car. The self check usually shows you ALL the module codes. Typically though the DIC will show you fewer codes than are actually stored in the computers. This is more true on 2000 and up models.
I can't tell you how many times I have had codes in the PCM that didn't show up on the self test but did show up on the scan tool.

History codes can be helpful in diagnosing intermittent problems, but depending on the code and the system they can me more of a distraction than a diagnostic tool.

But he was saying just the opposite: Codes do show up on the DIC but not on his mechanic's computer. Sounds like his mechanic doesn't have the right tool for the job!

No comments please... :D

Peteski

Please re-read the first part of my last post. But you could be correct, he didn't tell us what type of scanner the mechanic was using. If it isn't a factory scan tool.....

I'm not trying to be a wise-a$$ but I am a bit confused by your posting which says that one method gives you more codes than another. After reading the message several more times, I'm even more confused... Which gives more codes? A Factory Scan Tool or the diagnostic output on the DIC?

Sorry...

Peteski

On 2000 and up Devilles I have lost count of how many times I did a DIC check for "all codes" and got nothing. Then I hooked up the factory scan tool and found lots of them.
On an older car, like the '98 in question, I don't remember seeing this phenomenon.

My main point was that if he does a code check on the DIC he's going to get ABS, SIR, PCM, suspension, body control codes, etc. etc.
With a scan tool he's only going to see the codes that are in ONE module at a time. This might have lead him to his current state of confusion where he remembers seeing lots of codes on the DIC but the scan tool only shows one or two.
Plus based on who built the scan tool, it might not even have access to the codes in the body and suspension systems.

Sorry for the confusion, I hope this makes clear what I was trying to get accross.

To further clarify, when I said "U B and C codes" what I meant was U codes are communication codes, B codes are body codes and C codes are chassis. They all come from different modules under different conditions but show up on a "self test" even though they may not be stored in the PCM.
You could have 20 U, B and C codes but when reading PCM codes with a scan tool you could have none.
See what I mean?

Yup - it is clear now. Thanks Will!

Peteski