1999 GMC Pickup — 4L80E, No Line Rise

This problem and fix comes from Wilf Burnett from Wilf’s Transmissions in Vancouver Canada. The truck came in with severe clutch failure. They discovered a no-line-rise malfunction and proceeded to diagnose the problem. Their diagnosis confirmed that the PCM was not providing the correct signal to the pressure-control solenoid. A closer look revealed the security light for the PAT (passive anti-theft) was on. This particular vehicle was converted to propane and would run, even with the PAT system triggered. However, under this circumstance the PCM would not provide a line-rise signal. The fix was to reset the PAT system.

 

This certainly classifies as an uncommon problem but it does support the practice of making sure all systems are functioning properly before diagnosing a transmission failure.

 

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