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.

### Circuit/System Description

The data link connector (DLC) is a standardized 16-cavity connector. Design and location is dictated by an industry-wide standard. The following is required to be provided:

• | Scan tool power battery positive voltage at terminal 16

• | Scan tool power ground at terminal 4

• | Common signal ground at terminal 5

The scan tool will power up with the ignition OFF. Some modules, however, will not communicate unless the ignition is ON and the power mode master (PMM) module sends the appropriate power mode message.

### Reference Information

#### Schematic Reference

Data Communication Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Data Link Communications Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool References

Control Module References for Scan Tool Information

### Circuit/System Verification

1. Ignition OFF, test for less than 5 ohm between terminal 4 at the data link connector (DLC) and ground.

⇒ | If greater than the specified value, test the ground circuit for an open/high resistance.

2. Ignition OFF, test for less than 5 ohm between the DLC terminal 5 and ground.

⇒ | If greater than the specified value, test the ground circuit for an open/high resistance.

3. Ignition ON, test for B+ between the DLC terminals 16 and ground.

⇒ | If not the specified value, test the B+ circuit for a short to ground or an open/high resistance.

4. If all circuits test normal, refer to the scan tool user guide.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.