The preheat Relay controls the preheater from an electric signal from the Engine Control Module (ECM). This function is used to warm up the inlet air during cold conditions. This provides more reliable starting and reduces exhaust emissions during cold starts. Vehicles can be equipped with or without the preheater.

Conditions for diagnostic trouble code (DTC):
1) Output activated
2) Short circuit to battery voltage on A14.EB:25

Observable symptoms
1) Intake air heater (IAH) relay never activated
2) Difficult to start in extreme cold
3) White smoke at cold start

Probable cause
1) Engine wiring harness
2) Connector
3) Intake air heater (IAH) relay