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 Descriptors

DTC P0601: Control Module Read Only Memory (ROM)
DTC P1650: Control Module Internal Performance
DTC P1655: Control Module Internal Performance

### Circuit/System Description

This diagnostic applies to internal microprocessor integrity conditions within the engine control module (ECM). This diagnostic also addresses if the ECM is not programmed.

### Conditions for Running the DTC

#### DTC P0601

• | The ignition is ON, or the engine is running.

• | The DTCs run once an ignition cycle.

#### DTC P1650 and P1655

• | The ignition is ON, or the engine is running.

• | The DTCs run once an ignition cycle.

### Conditions for Setting the DTC

#### DTC P0601

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

#### P1650 and P1655

The ECM detects a low power counter error for greater than 3 seconds.

### Action Taken When the DTC Sets

• | DTC P0601 is a Type A DTC.

• | DTC P1650 is a Type C DTC.

• | DTC P1655 is a Type B DTC.

### Conditions for Clearing the DTC

• | DTC P0601 is a Type A DTC.

• | DTC P1650 is a Type C DTC.

• | DTC P1655 is a Type B DTC.

### Reference Information

#### Description and Operation

Engine Control Module Description

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

### Circuit/System Testing

Ignition ON, observe the DTC information with a scan tool. DTCs P0601, P1650, or P1655 should not set.

⇒ | If DTCs P0601, P1650, or P1655 failed this ignition, replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM replacement, setup, and programming