P1518

Schematic:

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.

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 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/Failure 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 a scan tool.

DIAGNOSTIC AIDS
Inspect for the following:

IMPORTANT: DTC P1518 sets if the battery voltage is low or the PCM is replaced/reflashed. If the customers 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.

The following could cause an intermittent condition:

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection.
Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Diagrams.
^ Damaged harness.
Inspect the wiring harness for damage. If the harness appears to be OK, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display may indicate the location of the fault. Refer to Wiring Repairs in Diagrams.
^ Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION

Steps 1 - 8:

Steps 9 - 19:

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.