Diagnostic Instructions

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

Circuit	Short to Ground	Open	Short to Voltage	Signal Performance
TP Sensor 1 Signal	P0122	P0122	P0123	P0121
TP Sensor 5V Reference	P0122	P0122	P0123	--
TP Sensor Low Reference	--	P0123	--	--

Typical Scan Tool Data

TP Sensor 1

Circuit	Short to Ground	Open	Short to Voltage
Parameter Normal Range: 4.63-0.18 V
TP Sensor 1 Signal	0 V	0 V	5 V
TP Sensor 5V Reference	0 V	0 V	5 V
TP Sensor Low Reference	--	5 V	--

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 5V 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 4V at idle to below 1V at wide open throttle (WOT). TP sensor 2 signal voltage increases from below 1V at idle to above 4V 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

Conditions for Setting the DTC

P0121

P0122

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

P0123

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

Action Taken When the DTC Sets

Conditions for Clearing the DTC

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References 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.
2. Ignition ON, observe the TP sensor 1 voltage parameter. The reading should be between 0.18-4.63V 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 Q38 throttle body. Allow sufficient time for the ECM to completely power down.
2. Ignition OFF, test for less than 5Ω between the low reference circuit terminal C and ground.

⇒	If greater than 5Ω, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20 ECM.

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

⇒	If less than 4.8V, test the 5V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

⇒	If greater than 5.2V, test the 5V 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 0.1V.

⇒	If greater than 0.1V, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the K20 ECM.

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

⇒	If less than 4.8V, test the TP sensor 1 signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

6. Ignition OFF, disconnect the harness connector at the K20 ECM.
7. Test for less than 5Ω on the TP sensor circuits between the following terminals:

•	ECM X1 5V reference circuit terminal 39 to terminal E.

•	ECM X1 signal circuit terminal 90 to terminal D.

⇒	If greater than 5Ω, 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 Q38 throttle body.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.