For 1990-2009 cars

### 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 detects a loss of data or invalid data, this diagnostic trouble code (DTC) sets.

### Conditions for Running the DTC

• | DTC P1517 is not set.

• | The ignition switch is in the crank or the run position.

• | The ignition voltage is greater than 5.23 volts.

### Conditions for Setting the DTC

• | Invalid or missing serial data messages are detected for a predetermined period of time.

• | All of the above conditions are met for less than 1 second.

### 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. If the customer's concern is slow cranking or no crank because the battery voltage is low, ignore DTC P1518. Clear any DTCs from memory that may have set from the low battery voltage condition.

• | DTC P1518 sets when there is a short to B+ on the TAC module ground circuit. Inspect the fuses for the circuits that are in the TAC module harness, i.e., cruise, brake. An inspection of the fuses may lead you to the circuit that is shorted to the TAC module ground circuit.

• | DTC P1518 sets if the TAC module ignition feed circuit is shorted to a B+ supply circuit. The TAC module stays powered-up when the ignition switch is turned OFF. When the ignition switch is turned ON, the TAC module is powered-up before the PCM. DTC P1518 sets because no communication is detected by the TAC module from the PCM. Inspect related circuits for being shorted to a B+ supply circuit.

• | Inspect the TAC module power and ground circuits and the TAC module/PCM serial data circuits for intermittent connections.

• | Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs could be set with no circuit or component conditions found during diagnostic testing.

• | When the TAC module detects a problem within the TAC system, more than one TAC system related DTC 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.

• | For an intermittent condition, refer to Intermittent Conditions .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step determines if the engine control relay is suppling a voltage to the ENG 1 circuit breaker .

2. 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 one set of the transistors are low, 0 volts, and the other set are high (B+). Therefore, if one 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.

3. When the TAC module detects a condition within the TAC system, more than one TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture Info.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Turn ON the ignition, with the engine OFF.
2. Remove the cover from the fuse relay center.
3. With a test lamp connected to ground, test both sides of the ETM circuit breaker.

Does the test lamp illuminate on at least one side of the circuit breaker?

--

Go to Step 3

Go to Ignition Relay Diagnosis

3 |

1. Turn OFF the ignition.
2. With a test lamp connected to ground, test for voltage at the ETM circuit breaker.

Does the test lamp illuminate?

--

Go to Step 22

Go to Step 4

4 | Install a scan tool. Is DTC P0606 also set? | -- | Go to DTC P0601, P0602, P0603, P0604, P0605, P0606, P0607, P1600, P1621, P1627, P1680, P1681, P1683, or P2610 | Go to Step 5
5 | Important: If the Driver Information Center is displaying Reduced Engine Power, proceed to step 6.

1. Start the engine.
2. Increase the engine speed to 3,000 RPM, if possible.
3. Monitor the Diagnostic Trouble Code (DTC) Info option using the scan tool.

Does the scan tool indicate this DTC failed this ignition?

--

Go to Step 6

Go to Diagnostic Aids

6 |

1. Turn OFF the ignition.
2. Disconnect the throttle actuator motor harness connector.
3. Turn ON the ignition, with the engine OFF.
4. Use a DMM in order to test for voltage at both throttle actuator motor control circuits.

Does the DMM indicate voltage on both circuits above the specified value?

8 V

Go to Step 12

Go to Step 7

7 |

1. Turn OFF the ignition.
2. Disconnect the TAC module.
3. Use a DMM in order to test both throttle actuator motor control circuits for continuity to ground.

Does the DMM indicate continuity to ground?

--

Go to Step 10

Go to Step 8

8 |

1. Turn OFF the ignition.
2. Remove the ETM circuit breaker.
3. Use a DMM in order to test the TAC side of the circuit breaker terminal for continuity to ground.

Does the DMM indicate continuity to ground?

--

Go to Step 9

Go to Step 11

9 |

1. Disconnect the TAC module 16-way harness connector.
2. Use a DMM in order to test the TAC side of the circuit breaker terminal for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 24

10 |

1. Disconnect the TAC module 16-way harness connector.
2. Use a DMM in order to test the throttle actuator motor control circuits for a short to ground at the TAC module 16-way harness connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 24

11 |

1. Turn OFF the ignition.
2. Disconnect the TAC module 16-way harness connector.
3. Use a DMM in order to test the TAC module ignition feed circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 24

12 |

1. Turn OFF the ignition.
2. Disconnect the TAC module 16-way connector.
3. Turn ON the ignition, with the engine OFF.
4. Use a DMM in order to test for a short to voltage at both throttle actuator motor control circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 13

13 |

1. Turn OFF the ignition.
2. Disconnect the TAC module 10-way harness connector.
3. Use a DMM in order to test for a short between each throttle actuator motor control circuit and all other TAC module circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 14

14 | Use a DMM in order to test for an open or high resistance in the TAC module ground circuit. 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 | Use a DMM in order to test for voltage on the serial data circuits at the TAC module 16-way harness connector. 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 |

1. Turn OFF the ignition.
2. Use a DMM in order to test both serial data circuits at the TAC module 16-way harness connector for continuity to ground.

Does the DMM indicate OL for both circuits?

--

Go to Step 20

Go to Step 17

17 |

1. Disconnect the PCM connector containing the TAC module serial data circuits.
2. Use a DMM in order to test both serial data circuits at the TAC module 16-way connector for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 18

18 | Use a DMM in order to test for a short between both serial data circuits and all other circuits at the PCM and TAC module harness connectors. 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 | Use a DMM in order to test for a short to voltage on both serial data circuits at the TAC module 16-way connector. 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 |

1. Disconnect the PCM connector that contains the TAC module serial data circuits.
2. Use a DMM in order to test each serial data circuit between the TAC module 16-way harness connector and the PCM harness connector for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 21

21 |

1. Reconnect the PCM.
2. Turn ON the ignition.
3. Use a DMM in order to test for voltage on the serial data circuit at the TAC module 16-way harness connector.

Does the DMM indicate voltage at the specified value?

0 V

Go to Step 25

Go to Step 24

22 |

1. Turn OFF the ignition.
2. Disconnect the 16-way TAC module harness connector.
3. Test the TAC module ignition positive voltage circuit for a short to battery voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 28

Go to Step 23

23 |

1. Turn ON the ignition.
2. Test both TAC motor circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

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 Connector Repairs 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 Connector Repairs 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 Electronic Throttle Actuator Control Module Replacement . Did you complete the replacement? | -- | Go to Step 28 | --
27 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 28 | --
28 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 29

Go to Step 2

29 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK