KEI FABRICATION
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- Joined
- Feb 12, 2024
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New to the forum. I just went through a successful solution that was a P 0300 random misfire code preventing the transmission torque converter from locking up.
History:
I purchased this 2003 Yukon XL 2500 6.0 4L80E used with 200K on it. When I first looked at it, there was no engine light on, but my scan tool showed the random misfire P 0300 code was present.
I have been driving (towing campers and car trailers) for 50,000 miles since I purchased it and never really had any issues until 245K.
From early on, at 70MPH the check engine light would flash, and within a few seconds it would stop flashing and everything was fine. Every time I checked the code it was P 0300. Even though it was flashing that it was misfiring, I never noticed any stumbling, spark knock, hesitation, or any other performance problem, so I ignored the flashing check engine light for the first 45K miles.
While returning from a 6000mile camping trip, I noticed the converter was not locking up as often as it should.
I also noticed that the check engine light was starting to flash sooner (at about 67 MPH). I did the typical quick fixes like plugs, wires, fuel filters, injector cleaner, coil checks etc. but no improvement. I still NEVER had any indication of any decrease in performance the entire time the P 0300 code was flashing, and I am almost always towing 6000lbs.
Eventually the converter stopped locking up at all while traveling at highway speeds.
While researching possible causes of the converter lock up problem, I learned that the P 0300 code will prevent the converter from locking up.
While talking to a GM tech friend, he said that at the higher milage vehicles experience wear in the timing chain. The cam sensor and crank trigger phasing falls out of the programed acceptable limit, and the PCM triggers the flashing check engine light, and the P 0300 code. The GM tech informed me that the advanced scan tools (like Snap ON) allow you to perform a Cam/Crank phasing relearn. This sets the limits to a new threshold based on the additional slop in the timing chain. I borrowed a Snap On scan tool and performed the cam/crank sensor relearn (took about 10 minutes) and then went for a test drive. The converter was locking up like it was new, and the check engine light never flashed again. That same day I got a call to tow a broken down car for a relative and the trans worked like new with a 2200lb trailer and a 3800lb car in tow.
This might be common knowledge for some, (maybe most) but I thought it might save someone hundreds of $ and time chasing the dreaded P 0300 random misfire code.
I can't tell you how relieved I am to have solved this problem. I have another several thousand mile trip planned this summer, and I really was convinced that I would be rebuilding the trans and replacing the converter this spring.
Obviously, if the problem comes back, I will need to replace the timing chain because additional wear/stretch must be happening. I will keep an eye on it.
If you have 175K plus on your LS powered truck, and are experiencing the P 0300 code, and not noticing any obvious performance issues, I would highly recommend starting with this procedure.
I hope this information is helpful to someone.
Thanks!
Mike.
History:
I purchased this 2003 Yukon XL 2500 6.0 4L80E used with 200K on it. When I first looked at it, there was no engine light on, but my scan tool showed the random misfire P 0300 code was present.
I have been driving (towing campers and car trailers) for 50,000 miles since I purchased it and never really had any issues until 245K.
From early on, at 70MPH the check engine light would flash, and within a few seconds it would stop flashing and everything was fine. Every time I checked the code it was P 0300. Even though it was flashing that it was misfiring, I never noticed any stumbling, spark knock, hesitation, or any other performance problem, so I ignored the flashing check engine light for the first 45K miles.
While returning from a 6000mile camping trip, I noticed the converter was not locking up as often as it should.
I also noticed that the check engine light was starting to flash sooner (at about 67 MPH). I did the typical quick fixes like plugs, wires, fuel filters, injector cleaner, coil checks etc. but no improvement. I still NEVER had any indication of any decrease in performance the entire time the P 0300 code was flashing, and I am almost always towing 6000lbs.
Eventually the converter stopped locking up at all while traveling at highway speeds.
While researching possible causes of the converter lock up problem, I learned that the P 0300 code will prevent the converter from locking up.
While talking to a GM tech friend, he said that at the higher milage vehicles experience wear in the timing chain. The cam sensor and crank trigger phasing falls out of the programed acceptable limit, and the PCM triggers the flashing check engine light, and the P 0300 code. The GM tech informed me that the advanced scan tools (like Snap ON) allow you to perform a Cam/Crank phasing relearn. This sets the limits to a new threshold based on the additional slop in the timing chain. I borrowed a Snap On scan tool and performed the cam/crank sensor relearn (took about 10 minutes) and then went for a test drive. The converter was locking up like it was new, and the check engine light never flashed again. That same day I got a call to tow a broken down car for a relative and the trans worked like new with a 2200lb trailer and a 3800lb car in tow.
This might be common knowledge for some, (maybe most) but I thought it might save someone hundreds of $ and time chasing the dreaded P 0300 random misfire code.
I can't tell you how relieved I am to have solved this problem. I have another several thousand mile trip planned this summer, and I really was convinced that I would be rebuilding the trans and replacing the converter this spring.
Obviously, if the problem comes back, I will need to replace the timing chain because additional wear/stretch must be happening. I will keep an eye on it.
If you have 175K plus on your LS powered truck, and are experiencing the P 0300 code, and not noticing any obvious performance issues, I would highly recommend starting with this procedure.
I hope this information is helpful to someone.
Thanks!
Mike.
