P1518

Circuit Description

The TAC Module and the PCM communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity but also adequate system voltage. This diagnostic monitors the accuracy of the serial data transmitted between the TAC Module and the PCM. If the PCM/TAC module detects a loss of data or invalid data, this DTC sets.

Conditions for Running the DTC

The ignition switch is in the crank or run position.

Conditions for Setting the DTC

^ Invalid or missing serial data messages are detected for a predetermined amount of time.
^ All of the above conditions met for less than 1 second.

Action Taken When the DTC Sets

^ The PCM will illuminate the MIL during the first trip in which the diagnostic runs and fails.
^ If equipped with traction control, the PCM will command the Electronic Brake and Traction Control Module (EBTCM) via the serial data circuit to turn OFF traction control and illuminate the TRACTION OFF lamp.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.

Conditions for Clearing the MIL/DTC

^ The PCM will turn the MIL OFF during the third consecutive trip in which the diagnostic has been run and passed.
^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the Scan Tool.

Diagnostic Aids

Important:
^ DTC P1518 sets if the battery voltage is low. If the customer's concern is slow cranking or no crank because battery voltage is low, ignore DTC P1518. Clear any DTCs from memory that may have set from the low battery voltage condition.
^ Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing/replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

Check the TAC Module power and ground circuits and the TAC Module/PCM serial data circuits for intermittent connections.

The following problems may cause an intermittent:

- Poor connections. Check for adequate terminal tension. Refer to wiring Repairs in Diagrams for proper procedure.
- Corrosion
- Mis-routed harness
- Rubbed through wire insulation
- Broken wire inside the insulation
- Inspect the connectors for signs of water intrusion. When this occurs, multiple DTCs should be set and no circuit or component problems can be located.
- For an intermittent condition, refer to Symptoms. Symptom Related Diagnostic Procedures
^ If a repair is complete and the DTC was cleared by using a scan tool on the same ignition cycle, the default action will not clear until an ignition cycle has occurred.
^ When the PCM/TAC module detects a problem within the ETC System other DTCs may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. keep this in mind when reviewing captured DTC info.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

19. When the PCM detects a problem within the ETC System other DTCs may set due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. keep this in mind when reviewing captured DTC info.