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P1221


















Circuit Description
The Throttle Position (TP) sensor is mounted on the throttle body assembly. The sensor is actually two individual Throttle Position sensors within one housing. Two separate signal, ground and 5 volt reference circuits are used to connect the TP sensor assembly and the Throttle Actuator Control (TAC) Module. The two sensors have opposite functionality. The TP sensor 1 signal voltage increases as the throttle opens, from below 1.0 volt at 0% throttle to above 3.5 volts at 100% throttle. The TP sensor 2 signal voltage decreases from around 3.8 volts at 0% throttle to below 1.0 volt at 100% throttle. Observe also that the signal circuit for TP Sensor 1 is pulled up to 5 volts and that the signal circuit for TP Sensor 2 is pulled to ground within the TAC Module.

Conditions for Running the DTC
^ DTCs P0606, P1517, P1518 not set.
^ Ignition switch in the crank or run position.
^ Ignition voltage greater than 5.23 volts.

Conditions for Setting the DTC
^ TP sensor 2 disagrees with TP sensor 1 by more than 7.5%.
^ All above conditions met for less than 1 second.

Action Taken When the DTC Sets
^ The PCM stores the DTC information into memory when the diagnostic runs and fails.
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
^ The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.
^ If no other TAC System DTCs are set, the TAC System operates in Reduced Engine Power mode. If certain TAC System DTCs are set at the same time, the TAC System either defaults to a more tightly restricted mode of operation if the TAC determines that limited safe operation is possible, or the TAC commands the engine to shut down.
^ The Driver Information Center displays a message.

Conditions for Clearing the MIL/DTC
^ The PCM turns the MIL OFF after three consecutive ignition cycles that the diagnostic runs and does not fail.
^ A last test failed (current DTC) clears when the diagnostic runs and does not fail.
^ A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important:
^ Remove any debris from the PCM/TAC module connector surfaces before servicing the PCM/TAC module. Inspect the PCM/TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM/TAC modules.
^ For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter kit J 35616-A. Using this kit prevents damage to the harness/component terminals.
^ The following may cause an intermittent:
- Poor connections
- Corrosion
- Mis-routed harness.
- Rubbed through wire insulation.
- Broken wire inside the insulation.
- Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs should be set and no circuit or component conditions can be located.
^ The APP sensor 1 and the TP sensor 1 5.0 volt reference circuits are internally connected within the TAC module.
^ The APP sensor 2 and the TP sensor 2 5.0 volt reference circuits are internally connected within the TAC module.
^ 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. Keep this in mind when reviewing captured DTC info.
^ For an intermittent, refer to Symptoms. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table.
3. Disconnect the Throttle Actuator connector before inserting fingers into the throttle bore. Re-install the air inlet duct after repairs are completed.
5. This step determines what TP sensor circuit caused the DTC.
6. This step tests the TP sensor 1 5.0 volt reference circuit for high resistance. The TP sensor 2 voltage should display 5.0 volts when you jumper the two circuits together. Observe, the use of TP sensor 2 signal is only for diagnosing the TP sensor 1 5.0 volt reference circuit.
7. This step tests the TP sensor 1 signal and ground circuit.
8. This step verifies the TP sensor 1 signal circuit. The voltage should go to 0 volts when grounded. Inspect the signal circuit for high resistance if the voltage does not go to 0 volts.
9. This step tests the TP sensor 2 5.0 volt reference circuit for high resistance. The TP sensor 2 voltage should display 5.0 volts when you jumper the two circuits together.
10. This step tests for the TP sensor signal circuit. The TP sensor 2 voltage should display 5.0 volts.
31. 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.

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