Circuit Description
The throttle actuator control (TAC) module and the powertrain control module (PCM) communicate using 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 detects a loss of data or invalid data, or if the throttle limit is exceeded while operating in the Reduced Engine Power mode, DTC P1518 sets.
Conditions for Running the DTC
| • | The ignition is in the crank or run position. |
| • | The ignition voltage is more than 5.23 volts. |
| • | The communication between the TAC module and the PCM must be valid. |
Conditions for Setting the DTC
| • | Invalid or missing serial data messages are detected for a predetermined period of time |
| OR |
| • | The throttle limit is exceeded while operating in the Reduced Engine Power mode. |
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 and/or the Failure Records. |
| • | The control module commands the TAC system to operate in the Reduced Engine Power mode. |
| • | A message center or an indicator displays Reduced Engine Power. |
| • | Under certain conditions the control module commands the engine OFF. |
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
| • | 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 . |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views and Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Is the voltage at the specified value for all sensors? | 0 V | 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 |
Is the resistance less than the specified value for both circuits? | 5ohms | Go to Step 6 | Go to Step 13 |
6 |
Does the voltage measure within the specified range? | 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 for a short to ground in the serial data circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the conditions? | -- | Go to Step 19 | Go to Step 17 |
10 | Repair the short to battery voltage in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- |
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 conditions? | -- | Go to Step 19 | Go to Step 18 |
12 | Repair the open or short to ground in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- |
13 | Repair the open or high resistance in the TAC module ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 19 | -- |
14 | Test the ETC ignition 1 voltage circuit for the high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 15 |
15 | Test for an intermittent and for a poor connection at the throttle body. 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 19 | Go to Step 16 |
16 | Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- |
17 | Test for an intermittent and for a poor connection at the powertrain control module (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 19 | Go to Step 18 |
18 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- |
19 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 20 |
20 |
Important: Be aware that repairing 1 individual condition may correct more than 1 DTC. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | ||
