Buick Regal: DTC P0121-P0123, P0222, P0223, P16A0-P16A2, or P2135

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• 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 Sensors 1-2 Not Plausible

Diagnostic Fault Information

Typical Scan Tool Data

Throttle Position Sensor 1

Throttle Position Sensor 2

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 into a representation of voltage signals that are occurring in the throttle body. The information is then displayed on a scan tool as the voltage inputs from TP sensors 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 500 - 6, 800 RPM.
• The engine coolant temperature (ECT) is -7 to +125ºC (19 - 257ºF).
• The intake air temperature (IAT) is -20 to +126ºC (-4 to +259ºF).
• 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 6.41 V and reduced power is not active.
• The DTCs run continuously when the above condition are met.

P16A0, P16A1, or P16A2

• DTC P06A3 is not set.
• The ignition is ON or the engine is operating.
• The run/crank voltage is greater than 6.41 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 6.41 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 within normal operating range for greater than 1 s.

P0122

The ECM detects the throttle position sensor 1 signal voltage is less than 0.33 V for greater than 1 s.

P0123

The ECM detects the throttle position sensor 1 signal voltage is greater than 4.75 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 4.59 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 sensors 1 and 2 disagree greater than 7 - 10 percent for greater than 1 s.

OR

• The ECM detects that the TP sensor 1 and 2 learned minimum throttle position is greater than 5 percent of the 5 volt reference voltage.

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 Wiring Schematics (LTG)

Connector End View Reference

Component Connector End View Index

Description and Operation

Throttle Actuator Control (TAC) System Description

Electrical Information Reference

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

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 a DTC is set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

• Go to next step: If a DTC is not set

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

• If 90 % or greater

Refer to Throttle Body Cleaning.

• Go to next step: If less than 90 %

4. Verify that DTC P0122, P0123, P0222, P0223, P16A0, P16A1, P16A2, or P2135 are not set.

• If DTC P0122, P0123, P0222, P0223, or P2135 are the only DTCs set

Replace the Q38 Throttle Body.

• If DTC P16A0, P16A1, or P16A2 is set with any of the DTCs

Refer to Circuit/System Testing

• Go to next step: If none of the DTCs are set

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

• If Agree is not displayed

Test or replace the Q38 Throttle Body Assembly.

• Go to next step: If Agree is displayed

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

• If a DTC is set

Refer to Circuit/System Testing.

• Go to next step: If a DTC is not 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 table.

• If the MAP Sensor pressure is not in range

Refer to DTC P0106.

• Go to next step: If 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.

• Go to next step: 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.

• If the MAF Sensor parameter does not change smoothly and gradually

Refer to DTC P0101.

• Go to next step: If the MAF Sensor parameter changes smoothly and gradually

12. Verify the scan tool Boost Pressure Sensor pressure and BARO parameters are within 3 kPa (0.4 psi) with engine at idle.

• If the parameters are not within 3 kPa (0.4 psi)

Refer to DTC P0236.

• Go to next step: If the parameters are within 3 kPa (0.4 psi)

13. Verify the scan tool MAP Sensor parameter and the Boost Pressure Sensor parameter are within 20 kPa (2.9 psi) during a WOT acceleration at the time of the 1 - 2 shift.

• If the parameters are not within 20 kPa (2.9 psi)

Refer to DTC P0236

• Go to next step: If the parameters are within 20 kPa (2.9 psi)

14. 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.

15. Verify the DTC does not set.

• If the DTC sets

Refer to Circuit/System Testing.

• Go to next step: If the DTC does not set

16. 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 min for all vehicle systems to power down.

2. Test for less than 5 Ω between the low reference circuit terminal 4 and ground.

• If 5 Ω or greater

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for less than 2 Ω in the low reference circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K20 Engine Control Module.

• Go to next step: If less than 5 Ω

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.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the 5 V reference circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, 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.

• Go to next step: 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.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the signal circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, 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.

• Go to next step: If between 4.8 - 5.2 V

7. Test or replace the Q38 Throttle Body Assembly.

Repair Instructions

• Throttle Body Assembly Replacement
• 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 min for all vehicle systems to power down.

5. Ignition ON.

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

• If Agree is not displayed

Test or replace the Q38 Throttle Body Assembly.

• Go to next step: If Agree is displayed

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 set.

• If DTC sets

Refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

• Go to next step: If DTC does not set

8. All OK.

READ NEXT: