P0121

DTC P0121

Circuit Description

The throttle body assembly contains 2 throttle position (TP) sensors. The TP sensors are mounted to the throttle body assembly and are not serviceable. The TP sensors provide a signal voltage that changes relative to throttle blade angle. The engine control module (ECM) supplies the TP sensors with a common 5-volt reference circuit, a common low reference circuit, and 2 independent signal circuits.

The TP sensors have opposite functionality. TP sensor 1 signal voltage increases from below 1 volt at idle to above 4 volts at wide open throttle (WOT). TP sensor 2 signal voltage decreases from above 4 volts at idle to below 1 volt at WOT.

The ECM compares the signal of the TP sensor 1 and TP sensor 2 through the entire range. If the ECM detects a predetermined difference between sensor 1 and sensor 2, or a predetermined difference from the predicted range, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0121 Throttle Position (TP) Sensor 1 Performance

Conditions for Running the DTC

* The ignition 1 voltage is more than 7 volts.
* The TP sensor 1 voltage is between 0.17-4.6 volts.
* DTC P0121 runs continuously once the above conditions are met.

Conditions for Setting the DTC

* The TP sensor 1 disagrees more than 9 percent from TP sensor 2.
* The TP sensor 1 disagrees more than 9 percent from the predicted value.
* The above conditions are met for more than 4 seconds.

Action Taken When the DTC Sets

* The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
* The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

* The control module turns OFF the malfunction indicator lamp (MIL) after 4 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

* Use the J 35616 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.
* The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Engine Controls Component Views.
* If there is a condition with the TP sensors the ECM defaults to reduced power mode for the entire ignition cycle, even if the condition is corrected.
* For an intermittent condition, Refer to Intermittent Conditions. Intermittent Conditions

Test Description

Step 1 - Step 6:

Step 7 - Step 16:

Step 17 - Step 18:

The numbers below refer to the step numbers on the diagnostic table.
2. This step verifies that a condition exists. If there is a condition with a TP sensor circuit, the scan tool will display Disagree.
5. This step tests for high resistance in the 5-volt reference circuit of the TP sensors. If the DMM does not display more than the specified voltage there is high resistance in the circuit.
8. This step tests for high resistance in the low reference circuit of the TP sensor. The ECM must be completely powered down to obtain an accurate resistance reading. It may take up to 30 minutes for the ECM to power down after the ignition key is removed. Removal of the ECM/TCM fuse allows the ECM to power down completely.