DTC P1A20 GMC

Cause and Solution

The TCCM monitors the rear differential lock high control circuit, and the rear differential low reference circuit, for high and low voltage.The TCCM detects a high voltage when a low voltage is expected, or a low voltage when a high voltage is expected, on either the rear differential lock high control circuit or the rear differential low reference circuit.Fault must be present for 1 minute.