Clearing H codes ! 1992 LT-1
Thread Starter
Instructor
Joined: Nov 2012
Posts: 242
Likes: 4
From: Grand Island - Nebraska
Clearing H codes ! 1992 LT-1
Trying to clear history codes . Codes are h72,h26, h27, h64. At start up it reads C12, and after the car heats up up it lights up the ASR service and then eventually the service engine soon light..New Opti, plugs, wires, waterpump, MAP. FPR. I have heard that the throttle cable can cause this condition. Any thoughts or help? Thanks Forum.
Pro
Joined: Mar 2013
Posts: 628
Likes: 13
From: Indiana
Disconnect the battery for ten minutes. Codes are stored in volatile memory and will erase with loss of power. So will all your radio channels but at least your computer will be cleared. Afterwards start the car without hitting the gas pedal and let it idle for five minutes. Next take it out and go through the gears several times. Next hold it at 55 mph on the highway for five minutes straight with out varying your speed. This lets the computer learn the mixture codes for proper running and should be done whenever the computer is reset.
Thread Starter
Instructor
Joined: Nov 2012
Posts: 242
Likes: 4
From: Grand Island - Nebraska
Disconnect the battery for ten minutes. Codes are stored in volatile memory and will erase with loss of power. So will all your radio channels but at least your computer will be cleared. Afterwards start the car without hitting the gas pedal and let it idle for five minutes. Next take it out and go through the gears several times. Next hold it at 55 mph on the highway for five minutes straight with out varying your speed. This lets the computer learn the mixture codes for proper running and should be done whenever the computer is reset.
Pro
Joined: Mar 2013
Posts: 628
Likes: 13
From: Indiana
Here is a link to GM document that shows where to install the resistors. I don't know if there is a step-by-step write up or not.
http://www.corvetteforum.net/c4/dave8476/index4.shtml
http://www.corvetteforum.net/c4/dave8476/index4.shtml
Team Owner
Joined: Sep 2003
Posts: 25,398
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I don't believe a removal of power will clear "H" history codes in the CCM and I wouldn't go there. Here is a link to a complete diagnostic that can be done from the DIC module and there's an appropriate procedure also to clear CCM H codes. At the bottom there are also explanations of the H72 & 74 that are frequently noted after an after-market install. Do a read of this link a couple times so that you understand it well and there's quite a bit you can learn from it regarding your C4:
http://tech.corvettecentral.com/2011...trouble-codes/
The removal of power will clear the ECM but NOT I believe the CCM. The "re-learn" procedure mentioned should be sufficient. You certainly seem to have accumulated a rather large error code history so the clearing of the ECM is maybe quite wise and just start over!
http://tech.corvettecentral.com/2011...trouble-codes/
The removal of power will clear the ECM but NOT I believe the CCM. The "re-learn" procedure mentioned should be sufficient. You certainly seem to have accumulated a rather large error code history so the clearing of the ECM is maybe quite wise and just start over!
Last edited by WVZR-1; Mar 30, 2014 at 11:43 AM.
