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Tahoe / Yukon Service Manual

DTC P2122, P2123, P2127, P2128, or P2138

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5501018 Diagnostic Instructions Perform the Diagnostic System Check prior to using this diagnostic procedure: Diagnostic System Check - Vehicle Review the description of Strategy Based Diagnosis: Strategy Based Diagnosis An overview of each diagnostic category can be found here: Diagnostic Procedure Instructions DTC Descriptor DTC P2122 Accelerator Pedal Position Sensor Circuit Low DTC P2123 Accelerator Pedal Position Sensor Circuit High DTC P2127 Accelerator Pedal Position Sensor 2 Circuit Low DTC P2128 Accelerator Pedal Position Sensor 2 Circuit High DTC P2138 Accelerator Pedal Position Sensor and Sensor 2 Correlation Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performanc
5 V Reference — Terminal 6 @ Accelerator Pedal Position Sensor P06A3* P2122, P2138 P06A3* P2138
Signal — Terminal 5 @ Accelerator Pedal Position Sensor P2122 P2122, P2138 P2123, P2138 P2138
Low Reference — Terminal 4 @ Accelerator Pedal Position Sensor — P2123, P2138 — P2138
5 V Reference — Terminal 1 @ Accelerator Pedal Position Sensor 2 P0697* P2127, P2138 P0697* P2138
Signal — Terminal 2 @ Accelerator Pedal Position Sensor 2 P2127 P2127, P2138 P2128, P2138 P2138
Low Reference — Terminal 3 @ Accelerator Pedal Position Sensor 2 — P2128, P2138 — P2138
* Additional DTCs may set

Typical Scan Tool Data Accelerator Pedal Position Sensor

Circuit Short to Ground Open Short to Voltage
Operating Conditions: Ignition = On or Engine = Running Parameter Normal Range: 0.88 to 1.08 V
5 V Reference 0 V 0 V 0 V
Signal 0 V 0 V 4 to 5 V
Low Reference — 0 V —

Accelerator Pedal Position Sensor 2

Circuit Short to Ground Open Short to Voltage
Operating Conditions: Ignition = On or Engine = Running Parameter Normal Range: 0.39 to 0.59 V
5 V Reference 0 V 0 V 0 V
Signal 0 V 0 V 2 to 5 V
Low Reference — 0 V —

Circuit/System Description For an overview of the component/system, refer to: Intake Airflow Valve System Description

Circuit Description
5 V Reference Regulated voltage supplied by the control module.
Signal The control module input circuit has an internal resistance connected to ground.
Low Reference Grounded through the control module.
Component Description
B107 Accelerator Pedal Position Sensor The component contains 2 potentiometer(s) that varies its resistance proportionally with the position of the component/system: Accelerator Pedal The input voltage varies depending on the position of the sensor.
K20 Engine Control Module The control module controls a series of actuators to ensure optimal engine performance. The control
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Component Description
sensors, interprets the data and adjusts the engine actuators accordingly.

The pedal assembly contains 2 potentiometer-type accelerator pedal position sensors, which are not serviceable. When the accelerator pedal is pressed, the voltages of both sensors goes up. This redundant design enables the ECM to detect if the 2 signals indicate the same accelerator pedal position. Conditions for Running the DTC P2122, P2123, P2127, P2128 DTC P0697, P06A3 = Not set Ignition = On or Engine Running Ignition Voltage = Greater than 6.4 V Frequency the DTC runs = Continuously — After the running conditions are met P2138 DTC P0697, P06A3, P2122, P2123, P2127, P2128 = Not set Ignition = On or Engine Running Ignition Voltage = Greater than 6.4 V Reduced Engine Power = Inactive Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC P2122 Accelerator Pedal Position Sensor = Less than 0.46 V — For greater than 1 s P2123 Accelerator Pedal Position Sensor = Greater than 4.75 V — For greater than 1 s P2127 Accelerator Pedal Position Sensor 2 = Less than 0.32 V — For greater than 1 s P2128 Accelerator Pedal Position Sensor 2 = Greater than 2.6 V — For greater than 1 s P2138 Accelerator Pedal Position Sensor and Sensor 2 = Not within 5–10% of each other — For greater than 1 s Actions Taken When the DTC Sets DTCs listed in the DTC Descriptor category = Type A DTC Reduced Engine Power = Active Warning Message = Reduced Engine Power Conditions for Clearing the DTC DTCs listed in the DTC Descriptor category = Type A DTC Reference Information Schematic Reference Engine Controls Schematics Connector End View Reference Master Electrical Component List 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 Circuit/System Verification

  1. Ignition » On / Vehicle » In Service Mode
  2. Verify DTC P0641, P0651, P0697, P06A3 is not set. ⇒ If any of the DTCs are set Refer to: DTC P0641, P0651, P0697, or P06A3 ⇓ If none of the DTCs are set
  3. Verify the scan tool parameter: Accelerator Pedal Position Sensor Circuit Status = Okay Accelerator Pedal Position Sensor 2 Circuit Status = Okay ⇒ If not the specified state Refer to: Circuit/System Testing ⇓ If the specified state
  4. Verify the scan tool parameter: Accelerator Pedal Position Sensor = The value should not spike or drop out while moving the sensor through the entire range. Accelerator Pedal Position Sensor 2 = The value should not spike or drop out while moving the sensor through the entire range. ⇒ If the value spikes or drops out Refer to: Circuit/System Testing ⇓ If the value does not spike or drop out
  5. Verify the scan tool parameter: Accelerator Pedal Position Sensor and Sensor 2 = Agree ⇒ If not the specified state Refer to: Circuit/System Testing ⇓ If the specified state
  6. Verify the scan tool parameter: Accelerator Pedal Position Sensor & Accelerator Pedal Position Sensor 2 = The value should not spike or drop out. Perform the action while monitoring the parameter: Wiggle the harness and connector: B107 Accelerator Pedal Position Sensor Wiggle the harness and connector: K20 Engine Control Module ⇒ If the value spikes or drops out Repair as necessary » Wiring / Terminal(s) / Electrical Connector(s) ⇓ If the value does not spike or drop out
  7. 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. Verify the DTC does not set. ⇒ If the DTC sets Refer to: Circuit/System Testing ⇓ If the DTC does not set
  8. All OK. Circuit/System Testing
  1. Ignition/Vehicle & All vehicle systems » Off
  2. Disconnect the electrical connector: B107 Accelerator Pedal Position Sensor
  3. Test for less than 5 Ω between the test points: { Accelerator Pedal Position Sensor } Low Reference circuit terminal 3 & Ground { Accelerator Pedal Position Sensor 2 } Low Reference circuit terminal 4 & Ground ⇒ If 5 Ω or greater 3.1. Disconnect the appropriate electrical connector: K20 Engine Control Module 3.2. Test for less than 2 Ω between the test points: { Accelerator Pedal Position Sensor } Low Reference circuit terminal 3 @ Component harness & The other end of the circuit @ Control module harness { Accelerator Pedal Position Sensor 2 } Low Reference circuit terminal 4 @ Component harness & The other end of the circuit @ Control module harness ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Replace the component: K20 Engine Control Module ⇓ If less than 5 Ω
  4. Ignition » On / Vehicle » In Service Mode
  5. Test for 4.8 to 5.2 V between the test points: { Accelerator Pedal Position Sensor } 5 V Reference circuit terminal 1 & Low Reference circuit terminal 3 { Accelerator Pedal Position Sensor 2 } 5 V Reference circuit terminal 6 & Low Reference circuit terminal 4 ⇒ If less than 4.8 V 5.1. Ignition/Vehicle » Off 5.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 5.3. Test for infinite resistance between the test points: { Accelerator Pedal Position Sensor } 5 V Reference circuit terminal 1 @ Component harness & Ground { Accelerator Pedal Position Sensor 2 } 5 V Reference circuit terminal 6 @ Component harness & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇓ If infinite resistance 5.4. Test for less than 2 Ω between the test points: { Accelerator Pedal Position Sensor } 5 V Reference circuit terminal 1 @ Component harness & The other end of the circuit @ Control module harness { Accelerator Pedal Position Sensor 2 } 5 V Reference circuit terminal 6 @ Component harness & The other end of the circuit @ Control module harness ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Replace the component: K20 Engine Control Module ⇒ If greater than 5.2 V 5.1. Ignition/Vehicle » Off 5.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 5.3. Ignition » On / Vehicle » In Service Mode 5.4. Test for less than 1 V between the test points: { Accelerator Pedal Position Sensor } 5 V Reference circuit terminal 1 @ Component harness & Ground { Accelerator Pedal Position Sensor 2 } 5 V Reference circuit terminal 6 @ Component harness & Ground ⇒ If 1 V or greater » Repair the short to voltage on the circuit. ⇒ If less than 1 V » Replace the component: K20 Engine Control Module ⇓ If between 4.8 and 5.2 V
  6. Verify the scan tool parameter: Accelerator Pedal Position Sensor = Less than 0.2 V Accelerator Pedal Position Sensor 2 = Less than 0.2 V ⇒ If 0.2 V or greater 6.1. Ignition/Vehicle » Off 6.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 6.3. Ignition » On / Vehicle » In Service Mode 6.4. Test for less than 1 V between the test points: { Accelerator Pedal Position Sensor } Signal circuit terminal 2 @ Component harness & Ground { Accelerator Pedal Position Sensor 2 } Signal circuit terminal 5 @ Component harness & Ground ⇒ If 1 V or greater » Repair the short to voltage on the circuit. ⇒ If less than 1 V » Replace the component: K20 Engine Control Module ⇓ If less than 0.2 V
  7. Connect a 3 A fused jumper wire between the test points: { Accelerator Pedal Position Sensor } Signal circuit terminal 2 & 5 V Reference circuit terminal 1 { Accelerator Pedal Position Sensor 2 } Signal circuit terminal 5 & 5 V Reference circuit terminal 6
  8. Verify the scan tool parameter: Accelerator Pedal Position Sensor = Greater than 4.8 V Accelerator Pedal Position Sensor 2 = Greater than 4.8 V ⇒ If 4.8 V or less 8.1. Ignition/Vehicle » Off & Remove » Jumper wire(s) 8.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 8.3. Test for infinite resistance between the test points: { Accelerator Pedal Position Sensor } Signal circuit terminal 2 @ Component harness & Ground { Accelerator Pedal Position Sensor 2 } Signal circuit terminal 5 @ Component harness & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇓ If infinite resistance 8.4. Test for less than 2 Ω between the test points: { Accelerator Pedal Position Sensor } Signal circuit terminal 2 @ Component harness & The other end of the circuit @ Control module harness { Accelerator Pedal Position Sensor 2 } Signal circuit terminal 5 @ Component harness & The other end of the circuit @ Control module harness ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Replace the component: K20 Engine Control Module ⇓ If greater than 4.8 V
  9. Test or replace the component: B107 Accelerator Pedal Position Sensor Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Accelerator Pedal Replacement For control module replacement, programming, and setup refer to: Control Module References