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#3003 - 04/18/09 12:29 PM DTC P1518 Throttle Actuator Control (TAC) Module  
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DTC P1518 Throttle Actuator Control (TAC) Module Serial Data Circuit

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 malfunction indicator lamp (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 OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has 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:

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

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.


Loose terminal connection

- Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

- Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

Test Description

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

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.


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#3004 - 04/18/09 01:25 PM Re: DTC P1518 Throttle Actuator Control (TAC) Module [Re: teamzr1]  

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This code has been a mother for me, lots of conditions can effect the serial circuit from bad grounds to a faulty ignition switch. In my case I used these troubleshooting steps not included here but following where you left off to get to a bad TAC module if I did it correctly. I will try to borrow a TAC module to test. Thanks JR good information as always.

Mark

#3005 - 04/18/09 03:02 PM Re: DTC P1518 Throttle Actuator Control (TAC) Module [Re: ]  
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teamzr1 Offline
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teamzr1  Offline
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Can be a common data chatter problem where the TAC is fine but data to or from it gets wacked on the data bus so it is wrongly assumed TAC is failing.

Common when flashing like the PCM that hogs the Starbus while TAC tries to send out a keepalive frame but bus is too busy with all the flash data frames and falsely trips a P1518 and why GM content says at times this P1518 DRC can be ignored.

If clearly the DTC a few times does not clear the error then issue has to be looked into with more depth.


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