Diagnostic Aids

The PCM/TCM relies on Vehicle Speed Sensor Buffer Module (DRAC) to indicate what gear range has been selected. DRAC must be functioning properly or DTC 85 may be set. Check all connections, especially those at the transmission pass-thru connector. Compare scan tool gear ratio reading to specifications in GEAR RATIO table.

Fig 1: DTC 85 Schematic - 1993

Courtesy of GENERAL MOTORS CORP.

Fig 2: DTC 85 Flow Chart - 1993

Courtesy of GENERAL MOTORS CORP.