Diagnostic Aids

When attempting to diagnose an intermittent problem, use scan tester to review supplemental diagnostic information. Supplemental data (scan tester MALF HISTORY) can be used to help duplicate an intermittent problem. Using Diagnostic Service Probe (12092782) allows voltage to be read on wires without disconnecting connectors. Compare scan coolant signal with scan intake air temperature signal. On a vehicle which has cooled overnight, temperatures should be within 4°C of each other.

Fig 1: Code 25 Schematic IAT Sensor Circuit (High Temperature Indicated)

Fig 2: Code 25 Diagnostic Flow Chart IAT Sensor Circuit (High Temperature Indicated)