P1518
DTC P1518 Throttle Actuator Control (TAC) Module Serial Data Circuit
Circuit Description
The throttle actuator control (TAC) module and the powertrain control module (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 a loss of data or invalid data is detected, this DTC will set.
Conditions For Running the DTC
* The ignition is in the crank or run position.
* The ignition voltage is more than 5.23 volts.
Conditions for Setting the DTC
* Invalid or missing serial data messages are detected for a predetermined amount of time.
* Above condition met for less than 1 second.
Action Taken When the DTC Sets
* The PCM will illuminate the malfunction indicator lamp (MIL) and the Reduced Engine Power light will be on when this diagnostic fails.
* The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.
* If no other TAC System DTCs are set, the TAC System will operate in Reduced Engine Power mode, and this DTC will be stored. If certain TAC System DTCs are set at the same time, the TAC System will either default to a more tightly restricted mode of operation if it is determined that limited safe operation is possible, or command engine shut down.
Conditions for Clearing the MIL/DTC
* The PCM will turn the MIL OFF after 3 consecutive drive trips that the diagnostic runs and does not fail.
* 40 consecutive warm-up cycles has occurred
A History DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
* A last test failed (current DTC) will clear when the diagnostic runs and does not fail.
* PCM battery voltage is interrupted.
Important: The clear DTC info function may have to be performed twice in order to clear a throttle actuator Control System DTC.
* Using a scan tool
Diagnostic Aids
* Inspect for the cause of intermittents. An intermittent may be caused by the following conditions:
- Poor connections
- Corrosion
- Misrouted harness
- Rubbed through wire insulation
- Broken wire inside the insulation
- Water intrusion
* Inspect for intermittent connections at the TAC module power and ground circuits and the TAC Module/PCM serial data circuits.
* Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs should be set and no circuit or component problems can be located.
* Inspect for adequate terminal tension. Refer to Wiring Repairs Wiring Repairs in Wiring Systems.
* Inspect for further causes of intermittents. Refer Symptoms Symptoms.
* If a repair is completed and the DTC was cleared using a scan tool on the same ignition cycle, the default action will not clear until an ignition cycle has occurred.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. If this DTC does not Fail This Ignition, continue to monitor this DTC status while moving related harnesses and connectors. Refer to Diagnostic Aids if the harness movement causes this DTC to set.
16. At this point you have ruled out the harness as the cause of the problem. Since there is no method to verify the transmission of serial data with commonly available tools, it is most cost effective to replace the TAC module first. Refer to Electronic Throttle Actuator Control Module Replacement Service and Repair If the fault is still present after replacing the TAC module, reinstall the original TAC module and replace the PCM. Refer to Powertrain Control Module Replacement Service and Repair.
19. When a problem is detected within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests run continuously on this system. It is possible that locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing captured DTC info.
