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 test 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, this DTC sets.
Important: Reprogramming the PCM may cause a communication error between the PCM and the TAC. If the PCM detects a communication error, DTC P1518 sets. Clear any DTCs from the memory that may have been set by Reprogramming.
The numbers below refer to the step numbers on the diagnostic table.
This step determines if the ignition relay is supplying a voltage to the ETC/ECM fuse.
Increasing the engine speed to 3,000 RPM aids in locating a shorted throttle actuator motor control circuit. Depending on the polarity of the throttle actuator motor transistors, this DTC may not set with a fault in the control circuits. The throttle actuator motor is a bi-directional DC motor. Raising the engine speed changes the polarity of the transistors in the throttle actuator motor. This occurs because 1 set of the transistors are low, 0 volts, and the other set are high, B+. Therefore, if 1 set of transistors are at a low voltage and the corresponding circuit is shorted low, DTC P1518 will not set. When the polarity of the transistors change, this DTC sets. If this DTC does not fail this ignition, continue to monitor this DTC status while moving related harnesses and connectors.
Locating and repairing an individual condition may correct more than 1 DTC.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module (PCM) Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Does the test lamp illuminate on at least 1 side of the fuse? | -- | Go to Step 3 | Go to Ignition Relay Diagnosis | |
3 |
Does the test lamp illuminate? | -- | Go to Step 22 | Go to Step 4 |
4 | Connect a scan tool. Is DTC P0604 also set? | -- | Go to DTC P0601-P0607, P1600, P1621, P1627, P1680, P1681, P1683, or P2610 | Go to Step 5 |
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Important: If the Driver Information Center is displaying Reduced Engine Power, go to step 6.
Does the scan tool indicate this DTC failed this ignition? | -- | Go to Step 6 | Go to Diagnostic Aids | |
6 |
Does the DMM indicate voltage on both circuits above the specified value? | 1 V | Go to Step 12 | Go to Step 7 |
7 |
Does the DMM indicate continuity to ground? | -- | Go to Step 10 | Go to Step 8 |
8 |
Does the DMM indicate continuity to ground? | -- | Go to Step 9 | Go to Step 11 |
9 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 24 |
10 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 24 |
11 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 24 |
12 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 13 |
13 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 14 |
14 | Test for an open or high resistance in the TAC module ground circuit with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 15 |
15 | Test for voltage on the serial data circuits at the TAC module 16-way harness connector with a DMM. Does the DMM indicate voltage within the specified values for both circuits? | 0-4.5 V | Go to Step 16 | Go to Step 18 |
16 |
Does the DMM indicate OL for both circuits? | -- | Go to Step 20 | Go to Step 17 |
17 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 18 |
18 | Test for a short between both serial data circuits and all other circuits at the PCM and TAC module harness connectors with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 19 |
19 | Test for a short to voltage on both serial data circuits at the TAC module 16-way connector with a DMM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 25 |
20 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 21 |
21 |
Does the DMM indicate voltage at the specified value? | 0 V | Go to Step 25 | Go to Step 24 |
22 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 23 |
23 |
Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 24 |
24 | Test for poor connections at the TAC module harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 26 |
25 | Test for poor connections at the PCM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 28 | Go to Step 27 |
26 | Replace the TAC module. Refer to Throttle Actuator Control (TAC) Module Replacement . Did you complete the replacement? | -- | Go to Step 28 | -- |
27 | Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement . Did you complete the replacement? | -- | Go to Step 28 | -- |
28 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 29 |
Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | ||