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 the PCM of the 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 period of time.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
Inspect for the following:
Important: DTC P1518 sets if the battery voltage is low or the PCM is replaced or reflashed. If the customer's concern is slow cranking, or if the engine is not cranking because the battery voltage is low, ignore DTC P1518. Clear any DTCs from memory that may have set from the low battery voltage condition.
If the condition is intermittent, refer to Intermittent Conditions .
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
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 Failure Records conditions. Does the scan tool indicate DTC P1518 failed this ignition? | -- | Go to Step 3 | Go to Diagnostic Aids |
3 |
Is voltage at or near the specified value? | 0 V | Go to Step 4 | Go to Step 10 |
4 |
Does the voltage measure at or near the specified value? | B+ | Go to Step 5 | Go to Step 12 |
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? | -- | Go to Step 6 | Go to Step 13 |
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 values? | 2-5 V | Go to Step 14 | Go to Step 7 |
7 | Does the voltage measure more than the specified value? | 5 V | Go to Step 11 | Go to Step 8 |
8 | Does the voltage measure less than the specified value? | 5 V | Go to Step 9 | -- |
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? | -- | Go to Step 18 | Go to Step 16 |
10 | Repair the short to battery voltage in the ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 18 | -- |
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? | -- | Go to Step 18 | Go to Step 17 |
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? | -- | Go to Step 18 | -- |
13 | Repair the open in the TAC module ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 18 | -- |
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? | -- | Go to Step 18 | Go to Step 15 |
15 | Replace the TAC module. Refer to Accelerator Pedal Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- |
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? | -- | Go to Step 18 | Go to Step 17 |
17 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 18 | -- |
18 |
Does the DTC run, and pass? | -- | Go to Step 19 | Go to Step 2 |
With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | ||
