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.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Important: If DTC P1120, P1220, P1221, P1515 or P1516 are set, refer to the appropriate DTC first for further diagnosis. Operate the vehicle within Fail Records conditions. 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 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 Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
10 | Repair the short to battery voltage in the ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
11 | Test for a short to voltage on the TAC module serial data circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
12 | Repair the open or short to ground in the ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
13 | Repair the open in the TAC module ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
14 | Inspect for a faulty serial data connections at the TAC module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. 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 Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
17 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . 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 applicable DTC | System OK |
