GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Powertrain On Board Diagnostic (OBD) System Check--Performance Engine, or Powertrain On Board Diagnostic (OBD) System Check--Ram Jet Engine 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.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

DLC B+

1

1

--

--

DLC Ground

--

1

--

--

1. Scan Tool Does Not Power Up

Circuit/System Description

The data link connector (DLC) is a standardized 16 cavity connector. The connector is designed to provide the following:

    • Scan tool B+ voltage at terminal 16
    • Scan tool ground at terminal 4
    • Common ground at terminal 5

Diagnostic Aids

    • The scan tool will power up with the ignition OFF. The engine control module will not communicate unless the ignition is ON.
    • If the B+ circuit, ground circuits, and connections of the DLC are functioning properly, the malfunction must be due to the scan tool/CANdi module.

Reference Information

Schematic Reference

Data Communication Schematics

Connector End View Reference

    •  Engine Control Module Connector End Views--Performance Engine
    •  Engine Controls Connector End Views--Performance Engine
    •  Engine Control Module Connector End Views--Ram Jet Engine
    •  Engine Controls Connector End Views--Ram Jet Engine

Engine Control Module 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 Reference

    •  Engine Control Module Scan Tool Information--Performance Engine for scan tool information.
    •  Engine Control Module Scan Tool Information--Ram Jet Engine for scan tool information.

Circuit/System Verification

Connect the scan tool to the data link connector (DLC). Attempt to power-up the scan tool. The scan tool should power-up.

Circuit/System Testing

  1. Ignition OFF, test for less than 2 ohms between the following ground circuits terminals of the DLC and ground:
  2. • terminal 4
    • terminal 5
    If greater than the specified range, repair the ground circuit for an open/high resistance.
  3. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 16 at the DLC and ground.
  4. If the test lamp does not illuminate, repair the voltage supply circuit for a short to ground or an open/high resistance.
  5. If all circuits test normal, refer to the scan tool/CANdi module user guide.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.