Data Link Connector Diagnosis

CIRCUIT DESCRIPTION
The diagnostic tables in this section are, by design, for use with a scan tool. If the scan tool is inoperative, correct the scan tool before beginning any other diagnostic procedures. The DLC connector powers the scan tool, DLC terminal 16 provides the B+ power. DLC terminal 4 provides the ground for the scan tool°s power supply. DLC terminal 5 is an additional ground for serial data. Serial data for Powertrain diagnostics is on DLC terminal 7.

Part 1 Of 2:

Part 2 Of 2:

TEST DESCRIPTION
The number(s) below refer to the step number(s) on the Diagnostic Table.
2. If the ground circuit on DLC terminal 4 opens after the Scan Tool is up and running, the screen will go blank but the Scan Tool may remain on. If there is no ground at terminal 4 initially, the Scan Tool will not power up.
9. Some of the older Scan Tool receive power through a separate power cord from the cigar lighter. If you use this type of Scan Tool and the tool will not power up, check the cigar lighter socket for damage or a poor connection. Refer to Cigar Lighter Testing and Inspection for further details.
13. If there is no communication between the TCM and the Scan Tool, no data will be displayed. Serial Data is disrupted when the system voltage is below 9.0 Volts or above 16.0 Volts. A Scan Tool will not display the data if the system voltage is outside of this range. If no data is displayed with the engine running, but the data is displayed with the ignition ON, engine OFF, high system voltage (overcharging) may be at fault. If this is the case, the Scan Tool should display DTC P0560 System Voltage with the ignition ON and the engine OFF,
15. Try the Scan Tool on another Catera if one is available. The Catera uses ISO serial data and communicates with the Scan Tool on DLC terminal 7. Most other GM OBD 11 vehicles use Class 2 serial data on DLC terminal 2. Therefore, testing the Scan Tool on a vehicle that uses a different serial data system will not verify that the tool can communicate properly on terminal 7. An alternate approach is to try a different Scan Tool on the same vehicle if one is available. Before trying a different Scan Tool, check for a poor connection between the DLC and the Scan Tool cable.

Refer to General Electrical Diagnosis Procedures in Diagnostic Aids.

18. Before trying a different Scan Tool, check for a poor connection between the DLC and the Scan Tool cable.