Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 2. Repeat the command as many times as necessary. When the glow plugs are commanded ON by the scan tool, an internal PCM timer protects the glow plugs from damage by cycling the plugs ON for 3 seconds and OFF for 12 seconds. After the 12 seconds has elapsed, the glow plugs can be commanded ON again.
2. 9. If no trouble is found in the control circuit or in the connection at the PCM, the PCM maybe malfunctioning. This is an extremely unlikely failure.

Fig 1: DTC P1643

Courtesy of GENERAL MOTORS CORP.