For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P0800: Active Transfer Case (ATC) Control Module Requested MIL Illumination

### Circuit/System Description

This diagnostic trouble code (DTC) indicates that an emission related transmission DTC set in the active transfer case (ATC) control module. The engine control module (ECM) receives the ATC information over the serial data circuit. The ECM turns ON the malfunction indicator lamp (MIL) when the ATC sends a message over the serial data circuit requesting MIL illumination. The DTC information for the ECM will only display DTC P0800, but the freeze frame/failure records data will display the transmission DTC that set.

### Conditions for Running the DTC

• | The ignition is ON or the engine is operating.

• | DTC P0800 runs continuously.

### Conditions for Setting the DTC

The ECM receives a serial data message, from the ATC, in order to illuminate the MIL.

### Action Taken When the DTC Sets

DTC P0800 is a Type A DTC.

### Conditions for Clearing the DTC

DTC P0800 is a Type A DTC.

### Reference Information

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

Important: Correct any Engine Controls DTCs before diagnosing ATC DTCs.

1. DTC P0800 is an informational DTC. If there are no Engine Controls DTCs, refer to Diagnostic Trouble Code (DTC) List - Vehicle for diagnosis of ATC DTCs.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.