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 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 and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the MIL 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 Body and Accessories 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 . |
| • | 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.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 | If DTC P1120, P1220, P1221, P1515 or P1516 are set, refer to the appropriate DTC first for further diagnosis.
Does the scan tool indicate DTC P1518 failed this ignition? | -- | Go to Diagnostic Aids | |
3 |
Does voltage at or near the specified value? | 0 V | ||
4 |
Does the voltage measure at or near the specified value? | B+ | ||
5 | Test the TAC Module ground circuits using a J 35616-200 test lamp that is connected to B+. Does the test lamp illuminate when probing both circuits? | -- | ||
6 | Test for voltage between both TAC Module serial data circuits and a good ground using a DMM. Does the voltage measure within the specified range? | 2-5 V | ||
7 | Does the voltage measure more than the specified range? | 2-5 V | ||
8 | Does the voltage measure less than the specified range? | 2-5 V | -- | |
9 | Test for an open or short to ground in the serial data circuit. Refer to Wiring Repairs . Did you find and correct the condition? | -- | ||
10 | Repair the short to voltage in the ignition feed circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | -- | |
11 | Test for a short to voltage on the TAC Module serial data circuit. Refer to Wiring Repairs . Did you find and correct the condition? | -- | ||
12 | Repair the open or short to ground in the ignition feed circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | -- | |
13 | Repair the open in the TAC Module ground circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | -- | |
14 | Inspect for a faulty serial data connections at the TAC Module. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | ||
15 | Replace the TAC Module. Refer to Accelerator Pedal Replacement . Did you complete the replacement? | -- | -- | |
16 | Inspect for faulty connections at the PCM. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | ||
17 |
Important: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Did you complete the replacement? | -- | -- | |
18 |
Does the DTC reset? | -- | ||
Does the scan tool indicate any DTCs set that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
