P0123

DTC P0121, P0122, or P0123

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.

DTC Descriptors
DTC P0121
- Throttle Position (TP) Sensor 1 Performance

DTC P0122
- Throttle Position (TP) Sensor 1 Circuit Low Voltage

DTC P0123
- Throttle Position (TP) Sensor 1 Circuit High Voltage

Diagnostic Fault Information





Typical Scan Tool Data





Circuit/System 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 decreases from above 4 volts at idle to below 1 volt at wide open throttle (WOT). TP sensor 2 signal voltage increases from below 1 volt at idle to above 4 volts at wide open throttle.

The ECM compares the signal of the TP sensor 1 and TP sensor 2 through the entire operating range.

Conditions for Running the DTC

* The system voltage is more than 7 volts.
* The TP sensor 1 voltage is between 0.18-4.63 volts.
* DTCs P0121, P0122 and P0123 run continuously when the above conditions are met.

Conditions for Setting the DTC

P0121
* The TP sensor 1 disagrees more than 6.3 percent from TP sensor 2 for over 140 ms.
* The TP sensor 1 disagrees more than 9 percent from the throttle position calculated from mass air flow (MAF) signal for over 280 ms.

P0122

The TP sensor 1 voltage is less than 0.18 volt for over 140 ms.

P0123

The TP sensor 1 voltage is more than 4.63 volts for over 140 ms.

Action Taken When the DTC Sets

* DTC P0121 is a Type B DTC.
* DTC P0122 and P0123 are Type A DTCs.
* 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.

Conditions for Clearing the DTC

* DTC P0121 is a Type B DTC.
* DTC P0122 and P0123 are Type A DTCs.

Reference Information
Schematic Reference

Engine Controls Schematics (Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Diagnostic Trouble Code Descriptions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Verification

1. If DTC P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698, or P0699 are set, refer to DTC P0641-P0643, P0651-P0653, or P0697-P0699 (P0641).
2. Ignition ON, observe the TP sensor 1 voltage parameter. The reading should be between 0.18-4.63 volts and change with accelerator pedal input.
3. Observe the TP sensor 1 and 2 parameter. The scan tool should indicate agreement.
4. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC, or within the conditions that you observed from the Freeze Frame/Failure Records.

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the throttle body. Allow sufficient time for the ECM to completely power down.
2. Ignition OFF, test for less than 5 ohms between the low reference circuit terminal C and ground.

• If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal E and ground.

• If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
• If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Verify the scan tool TP sensor 1 voltage is less than 0.1 volt.

• If greater than 0.1 volt, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the ECM.

5. Install a 3A fused jumper wire between the signal circuit terminal D and the 5-volt reference circuit terminal E of the TP sensor 1, verify the TP sensor 1 voltage is greater than 4.8 volts.

• If less than 4.8 volts, test the TP sensor 1 signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

6. Ignition OFF, disconnect the harness connector at the ECM.
7. Test for less than 5 ohms on the TP sensor circuits between the following terminals:

* ECM X1 5-volt reference circuit terminal 39 to terminal E.
* ECM X1 signal circuit terminal 90 to terminal D.

• If greater than 5 ohms, repair the affected circuit.

8. Test for infinite resistance between TP sensor 1 signal circuit terminal D and TP sensor 2 signal circuit terminal F.

• If less than infinite resistance, repair the short between TP sensor 1 signal circuit and TP sensor 2 signal circuit.

9. If all circuits test normal, replace the throttle body.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Throttle Body Assembly Replacement (Removal and Replacement)
* Control Module References (Programming and Relearning) for ECM replacement, setup, and programming