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I have a 4L80E in a 91 C3500 dually and the converter will momentarily unlock and then lock right back up. It don't show any codes and has no pattern. Operates very well otherwise. Any suggestions?? Thanks.
Make sure your brake light switch is adjusted and not shorting. It's the 1st thing we check when a converter doesn't lock or keeps onlocking. When the brake light is activated the converter unlocks to allow slippage. And it will not cause a code, because that's the way it's suppose to work. Hope that's your case. Luck.