Diagnostic Aids

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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.
When there is a short to battery voltage on the TAC module ground circuit. Inspect the fuses for the circuits that are in the TAC module harness, (i.e., cruise or brake). An inspection of the fuses may lead you to the circuit that is shorted to the TAC module ground circuit.
If the TAC module ignition feed circuit is shorted to a battery voltage supply circuit. The TAC module stays powered-up when the ignition switch is turned OFF. When the ignition switch is turned ON, the TAC module is powered-up before the PCM. DTC P1518 sets because no communication is detected by the TAC module from the PCM. Inspect related circuits for being shorted to a battery voltage supply circuit.

Inspect the TAC module power and ground circuits and the TAC module/PCM serial data circuits for intermittent connections.

Inspect the TAC module connectors for signs of water intrusion. If water intrusion occurs, multiple DTCs may set without any circuit or component conditions found during diagnostic testing.

When the TAC module detects a problem within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing an individual condition may correct more than 1 DTC. Remember this if you review the stored information in Capture Info.

For an Intermittent condition, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.