How do I reset the PCM on a 2001 Safari?

How do I reset the PCM on a 2001 Safari?

Postby aktrossen [OP] » February 27th 2019, 1:19am

I have a 2001 GMC safari 4.3L and I have been running pretty lean. I dont have any trouble codes and just passed smog but when I hook up my OBDII scanner my LTFT in both bank 1 and 2 are hitting +20% and higher. Honestly, it seems as though it runs quite well. I just replaced the oxygen sensors and catalytic converter which needed to be done and I have no vacuum leak. THis van has a lot of new stuff! When I did this repair, as usual, I took my scan tool and erased the codes. All the monitors cleared and the system was ready and I passed my smog but when I took it to a mechanic with an advanced scanner all my old DTC codes were still stored on the PCM. He didn't give me much good information on removing them but after a little research, I read that you need to disconnect the negative terminal overnight in order to drain the capacitors completely if you don't have the scanner that will perform this function for you. Is this true? Does anybody have any good information on clearing stored codes on the PCM? Thanks in advance!
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Re: How do I reset the PCM on a 2001 Safari?

Postby MechBob » February 27th 2019, 1:46am

OBD2 vehicles have 3 types of codes,soft,hard and memory.Only a very good scan tool can remove the memory,a cheaper one sometimes does not even display them.Also,thrown into the mix,is all the "learn" features in the programming.You may have fixed the vehicle properly,but it fights the "Learn".Found this out the hard way,on a first generation Trundra.The procedure is to clear codes(factory scanner),then unhook battery for 30 minutes,then clear codes again(even if it shows none).You really do not have to wait 30 minutes,just unhook the positive cable,short it to ground,it will dump all the caps.
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Re: How do I reset the PCM on a 2001 Safari?

Postby aktrossen [OP] » February 27th 2019, 1:59am

Thanks MechBob! I appreciate the comment. Questions... So by taking the negative terminal off for a long period of time wont reset the PCM or it will only clear the soft and hard codes? By factory scanner do you mean any OBDII scanner or do I have to find a mechanic with a fancy scanner?
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Re: How do I reset the PCM on a 2001 Safari?

Postby MechBob » February 27th 2019, 2:11am

Unhooking the battery "may" clear soft codes.What you are doing/need to do,is clear the "Learn memory"[email protected] pcm's are complex,and replacing the bad part can still be affected by the memory,which sets the running parameters,over time.The factory scan tools(newer ones) mostly can do this,bunt not necessarily on older vehicles.The stored memory can give you false codes,even though you fixed the bad part.Go to any reputable shop that has a factory or snap-on,mac,etc quality scanner.Have them clear the codes.Unhook the positive cable,ground it out,hook back up.Start vehicle,let idle(a/c defrost off) until up to operating temps,if not already hot,then have shop recheck for codes.Should be none,but happens.Tell him to hit the "clear codes" button" even if there are no codes.Then go drive.Some aftermarket scanners will clear learn memory,but I doubt you want to spend a grand.That is my suggestion.If a problem still exsists,then you are starting with a clean slate,to find it.
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Re: How do I reset the PCM on a 2001 Safari?

Postby aktrossen [OP] » February 27th 2019, 3:08am

So frustrating honestly. I just want to fix the problem and move on
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Re: How do I reset the PCM on a 2001 Safari?

Postby MechBob » February 27th 2019, 3:19am

aktrossen wrote:So frustrating honestly. I just want to fix the problem and move on

Take it to a quality repair shop and write a check,instead of "throwing" parts at it.
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Re: How do I reset the PCM on a 2001 Safari?

Postby aktrossen [OP] » February 27th 2019, 3:36am

I dont mind doing the labor and all the repairs I have done were needed. I dont feel like I have been throwing parts at it trying to fix the problem. It is just the enhanced scanners and re learns for OBDII that annoy me. And I enjoy learning this stuff!
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Re: How do I reset the PCM on a 2001 Safari?

Postby 97cargocrawler » February 27th 2019, 9:49am

Disconnecting the battery for a good long while will initiate a relearn. Often longer than overnight.

The deep saved OBD codes are not causing you any performance issues...so why are you worried about them? Sounds more like what a seller would worry about...trying to cover something up. The saved history has no impact on current running parameters provided the issues that triggered them have been repaired and a relearn occured. You will always know when a relearn is happening..your van will run like total **** for a few minutes on startup and all monitors will be pending.

But alas the history is easily cleared with a Tech2 or similar diagnostic scanner.

Your lean condition will most likely remain after a relearn. That tends to be an oxygen starvation or timing issue. If not solved with physical repairs the only way to alter the mixture is by manipulating the lookup tables in the PCM which requires a sophisticated tuning programmer.
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Re: How do I reset the PCM on a 2001 Safari?

Postby konybravo » February 27th 2019, 2:25pm

I would seriously doubt, the ECM would get "confused"...I would rather suspect a mechanical issue, of some sort.Did you smoke the intake, to rule out a vacuum leak? And is the lean condition still present, at mid rpms- 2500-3000?
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Re: How do I reset the PCM on a 2001 Safari?

Postby aktrossen [OP] » March 2nd 2019, 8:40pm

Ok that’s makes sense maybe I’ll smoke it and see but I really don’t think it’s a vacuum leak. We’ll see
Original Poster [OP]
aktrossen
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Van Model Year: 2001
Van Make/Model: GMC Safari
Extra Info: 4.3L


 
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