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 provide an overview of each diagnostic category.

### DTC Descriptors

DTC P0601: Control Module Read Only Memory (ROM)
DTC P0604: Control Module Random Access Memory (RAM)
DTC P0605: Control Module Programming Read Only Memory (ROM)

### Circuit/System Description

This diagnostic applies to internal microprocessor integrity conditions within the engine control module (ECM).

### Conditions for Running the DTC

• | The ignition is ON, with the engine OFF or the engine is operating.

• | The DTCs run once an ignition cycle.

### Conditions for Setting the DTC

#### P0601

The ECM detects that the checksum calculation does not match the expected checksum.

#### P0604 or P0605

The ECM detects an internal condition for more than 3 seconds.

### Action Taken When the DTC Sets

DTCs P0601, P0604, and P0605 are Type B DTCs.

### Conditions for Clearing the DTC

DTCs P0601, P0604, and P0605 are Type B DTCs.

### Reference Information

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Description and Operation:

Engine Control Module Description

### Circuit/System Testing

Ignition ON, observe the DTC information with a scan tool.

⇒ | If DTCs P0601, P0604, or P0605 failed this ignition, replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for engine control module replacement, setup, and programming