LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Chevrolet >> 1994 >> Corvette Base, 2D Convertible, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> ECM/Pcm Code Charts >> Code 91, 1-4 Upshift Light >> Notes
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Code 91, 1-4 Upshift Light: Notes

When 1-4 shift light is energized, PCM is energizing 2nd-3rd blockout relay and gearshift can only be moved from 1st to 4th gear. This will occur only once per upshift cycle. Upshift can not be repeated until vehicle speed drops to less than one MPH.

NOTE: Test numbers refer to numbers on diagnostic chart.
  1. The 1-4 upshift light should not turn on. If light is on, circuit is shorted to ground or PCM is faulty.
  2. PCM should turn on 1-4 upshift light.
  3. Checks 1-4 upshift light circuit up to the PCM connector. If light illuminates, PCM connector is faulty or PCM does not have the ability to ground circuit.
scientia non olet · About LEMON Manuals