A/T - 4L80E No Upshift
TECHNICAL BULLETIN # 174TRANSMISSION: 4L80-E
SUBJECT: NO UPSHIFT
APPLICATION: GM
4L80-E NO UPSHIFT
A complaint of no upshift may be caused by a bad Transmission Input Speed Sensor. Reading data with a scan tool may show no vehicle speed signal. Replacing the output speed sensor, DRAC, and even the computer may not restore normal vehicle speed signal, if the computer does not recognize a valid transmission input speed signal.
High line pressure (no Force Motor current) may also occur depending on the software strategy. This condition is most common on two-wheel drive diesel applications, but may also apply to others. The software strategy used on the different models, years, and calibrations are too widely varied to be absolutely certain which vehicles may be affected in this manner.
Verify input speed sensor operation with a scanner before replacing other components needlessly.