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P0121




DTC P0121-P0123, P0222, P0223, P16A0-P16A2, or P2135

Diagnostic Instructions

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

DTC Descriptors
DTC P0121
- Throttle Position Sensor 1 Performance

DTC P0122
- Throttle Position Sensor 1 Circuit Low Voltage

DTC P0123
- Throttle Position Sensor 1 Circuit High Voltage

DTC P0222
- Throttle Position Sensor 2 Circuit Low Voltage

DTC P0223
- Throttle Position Sensor 2 Circuit High Voltage

DTC P16A0
- Sensor Communication Circuit Low Voltage

DTC P16A1
- Sensor Communication Circuit High Voltage

DTC P16A2
- Sensor Communication Circuit Performance

DTC P2135
- Throttle Position Sensor 1-2 Not Plausible

Diagnostic Fault Information






Typical Scan Tool Data











Circuit/System Description

The throttle body assembly contains a contact-less inductive throttle position sensing element that is managed by a customized integrated circuit. The throttle position sensor is mounted within the throttle body assembly and is not serviceable. The engine control module (ECM) supplies the throttle body with a 5 V reference circuit, a low reference circuit, an H-bridge motor directional control circuit, and an asynchronous signal/serial data circuit. The asynchronous signal means communication is only going from the throttle body to the ECM. The throttle body cannot receive data from the ECM over the signal/serial data circuit. The throttle position sensor provides a signal voltage that changes relative to throttle blade angle. The customized integrated circuit translates the voltage based position information into serial data using the Society of Automotive Engineers (SAE) J2716 Single Edge Nibble Transmission (SENT) protocol. The throttle position sensor information is transmitted between the throttle body and the ECM on the signal/serial data circuit. The ECM decodes the serial data signal and is used as voltages for throttle position sensor 1 and 2.

Conditions for Running the DTC

P0121
* DTCs P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0335, or P0336 is not set.
* The engine speed is between 400-6,200 RPM.
* The engine coolant temperature (ECT) is between -7 to +125°C (19-257°F).
* The intake air temperature (IAT) is between -20 to +125°C (-4 to +257°F).
* The DTC runs continuously when the above conditions are met.

P0122, P0123, P0222, P0223
* DTC P06A3 is not set.
* The ignition is ON or the engine is running.
* The run/crank or powertrain relay voltage is greater than 6.0 V and reduced power is not active.
* The DTCs run continuously when the above condition are met.

P16A0, P16A1, or P16A2
* The ignition is ON or the engine is operating.
* The run/crank voltage is greater than 6.4 V.
* The DTCs run continuously once the above conditions are met for greater than 1 s.

P2135
* DTCs P0122, P0123, P0222, P0223, or P06A3 are not set.
* The ignition is ON or the engine is running.
* The run/crank or powertrain relay voltage is greater than 6.0 V and reduced power is not active.
* The DTC runs continuously when the above conditions are met.

Conditions for Setting the DTC

P0121

The ECM detects that the throttle position sensor 1 voltage is stuck in range for greater than 1 s.

P0122

The ECM detects the throttle position sensor 1 signal voltage is less than 0.32 V for greater than 1 s.

P0123

The ECM detects the throttle position sensor 1 signal voltage is greater than 4.7 V for greater than 1 s.

P0222

The ECM detects the throttle position sensor 2 signal voltage is less than 0.25 V for greater than 1 s.

P0223

The ECM detects the throttle position sensor 2 signal voltage is greater than 4.6 V for greater than 1 s.

P16A0

The ECM detects a low voltage circuit condition on the throttle position sensor signal circuit for greater than 1 s.

P16A1

The ECM detects a high voltage circuit condition on the throttle position sensor signal circuit for greater than 1 s.

P16A2

The ECM detects an incorrect message was received over the throttle position sensor signal circuit for greater than 1 s.

P2135

The ECM detects that throttle position sensor 1 and 2 disagree greater than 7-10 percent for greater than 1 s.

Action Taken When the DTC Sets

* DTCs P0121 is a Type B DTC.
* DTCs P0122, P0123, P0222, P0223, P16A0, P16A1, P16A2, and P2135 are Type A DTCs.
* The ECM commands the throttle actuator control (TAC) system to operate in a Reduced Engine Power mode.
* A message center or an indicator displays Reduced Engine Power.
* Under certain conditions, the ECM commands the engine OFF.

Conditions for Clearing the DTC

* DTCs P0121 is a Type B DTC.
* DTCs P0122, P0123, P0222, P0223, P16A0, P16A1, P16A2, and P2135 are Type A DTCs.

Diagnostic Aids

* A high resistance condition on the throttle position and throttle actuator control circuits could cause a DTC to set.
* If the accelerator pedal is pressed to the wide open throttle position, the throttle blade angle or Throttle Position angle is limited to less than 40 percent.

Reference Information
Schematic Reference

Engine Controls Schematics [1][2]Electrical Diagrams
Connector End View Reference

Component Connector End Views Connector Views
Description and Operation

Throttle Actuator Control (TAC) System Description Throttle Actuator Control (TAC) System Description
Electrical Information Reference

* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs

DTC Type Reference

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

Control Module References Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON.
2. Verify that DTC P0601-P0606, P06A3, and P16F3 is not set.

• If any of the DTCs are set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

• If none of the DTCs are set

3. Verify the scan tool Throttle Body Idle Airflow Compensation parameter is less than 90 %.

• 90 % or greater
Refer to Throttle Body Inspection and Cleaning Procedures.

• If less than 90 %

4. Verify the scan tool Throttle Position Sensor 1 and Throttle Position Sensor 2 voltage parameters are greater than 0.0 V.

• If 0.0 V
Refer to Circuit/System Testing

• If greater 0.0 V

5. Verify the Throttle Position Sensors 1 and 2 Agree/Disagree parameter displays Agree while performing the Throttle Sweep Test with a scan tool.

• If Disagree
Test or replace the Q38 throttle body assembly.

• If Agree

6. Verify DTC P0121, P0122, P0123, P0222, P0223, P16A0, P16A1, P16A2, and P2135 is not set.

• If any of the DTCs are set
Refer to Circuit/System Testing

• If none of the DTCs are set

7. Determine the current vehicle testing altitude.
8. Verify the scan tool MAP Sensor pressure parameter is within range specified in the Altitude Versus Barometric Pressure Altitude Versus Barometric Pressure table.

• The MAP Sensor pressure is not in range
Refer to DTC P0106 P0106.

• The MAP Sensor pressure is within range

9. Engine idling.
10. Verify the scan tool MAP Sensor pressure parameter is between 26-52 kPa (3.8-7.5 psi) and changes with accelerator pedal input.

• If not between 26-52 kPa (3.8-7.5 psi) or does not change
Refer to DTC P0106 P0106.

• If between 26-52 kPa (3.8-7.5 psi) and changes

11. Verify the scan tool MAF Sensor g/s parameter changes smoothly and gradually as the engine speed is increased and decreased while performing the actions listed below.

1. Engine idling
2. Perform the scan tool snapshot function.
3. Increase the engine speed slowly to 3,000 RPM and then back to idle.
4. Exit from the scan tool snapshot and review the data.
5. Observe the MAF Sensor parameter frame by frame with a scan tool.

• The MAF Sensor parameter does not change smoothly and gradually
Refer to DTC P0101 P0101.

• The MAF Sensor parameter changes smoothly and gradually

12. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
13. Verify the DTC does not set.

• If the DTC sets
Refer to Circuit/System Testing

• If the DTC does not set

14. All OK

Circuit/System Testing

Note: Disconnecting the throttle body harness connector causes additional DTCs to set.

1. Ignition OFF, and all vehicle systems OFF, disconnect the harness connector at Q38 throttle body assembly. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 5 ohm between the low reference circuit terminal 4 and ground.

• If 5 ohm or greater

1. Ignition OFF, disconnect the harness connector at the K20 engine control module.
2. Test for less than 2 ohm in the low reference circuit end to end.

• If 2 ohm or greater, repair the open/high resistance in the circuit.
• If less than 2 ohm, replace the K20 engine control module.

• If less than 5 ohm

3. Ignition ON.
4. Test for 4.8-5.2 V between the 5 V reference circuit terminal 5 and ground.

• If less than 4.8 V

1. Ignition OFF, disconnect the harness connector at the K20 engine control module.
2. Test for infinite resistance between the 5 V reference circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance

3. Test for less than 2 ohm in the 5 V reference circuit end to end.

• If 2 ohm or greater, repair the open/high resistance in the circuit.
• If less than 2 ohm, replace the K20 engine control module.

• If greater than 5.2 V

1. Ignition OFF, disconnect the harness connector at the K20 engine control module, ignition ON.
2. Test for less than 1 V between the 5 V reference circuit and ground.

• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K20 engine control module.

• If between 4.8-5.2 V

5. Ignition ON.
6. Test for 4.8-5.2 V between the signal circuit terminal 3 and ground.

• If less than 4.8 V

1. Ignition OFF, disconnect the harness connector at the K20 engine control module.
2. Test for infinite resistance between the signal circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance

3. Test for less than 2 ohm in the signal circuit end to end.

• If 2 ohm or greater, repair the open/high resistance in the circuit.
• If less than 2 ohm, replace the K20 engine control module.

• If greater than 5.2 V

1. Ignition OFF, disconnect the harness connector at the K20 engine control module, ignition ON.
2. Test for less than 1 V between the signal circuit and ground.

• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K20 engine control module.

• If between 4.8-5.2 V

7. Test or replace the Q38 throttle body assembly.

Repair Instructions

* Throttle Body Assembly Replacement Removal and Replacement
* Control Module References Control Module References for engine control module replacement, programming, and setup

Repair Verification

1. Install any components that have been removed or replaced during diagnosis.
2. Perform any adjustments, programming or setup procedures that are required when a component is removed or replaced.
3. Clear the DTCs with a scan tool.
4. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down.
5. Ignition ON.
6. Verify the Throttle Position Sensors 1 and 2 Agree/Disagree parameter displays Agree while performing the Throttle Sweep Test with a scan tool.

• If Disagree
Test or replace the Q38 throttle body assembly.

• If Agree

7. If the repair was related to a DTC, duplicate the Conditions for Running the DTC and use the Freeze Frame/Failure Records, if applicable, in order to verify the DTC does not reset.

• If any DTC sets
Refer to Diagnostic Trouble Code (DTC) List - Vehicle Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

• If no DTC sets

8. All OK

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