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Tahoe / Yukon Service Manual

DTC P0405, P0406, or U0651

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5471111 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 P0405 Exhaust Gas Recirculation Valve Position Sensor Circuit Low DTC P0406 Exhaust Gas Recirculation Valve Position Sensor Circuit High DTC U0651 Lost Communication with Exhaust Gas Recirculation Valve Position Sensor Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performanc
5 V Reference P0641, U0651* U0651* P0641, U0651* —
Signal U0651* U0651* U0651* —
Low Reference — U0651* — —
* Additional DTCs may set

Circuit/System Description For an overview of the component/system, refer to: Exhaust Gas Recirculation (EGR) 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
Q14A Exhaust Gas Recirculation The assembly has several functions:
Valve 1 © 2023 Gener al Motors. All rights reserved.
Component Description
Exhaust Gas Recirculation Valve — A solenoid valve is an electro-mechanically operated valve. The valve is controlled by an electric current through the solenoid. EGR Position Sensor — The component contains 1 potentiometer(s) that varies its resistance proportionally with the position of the component/system: EGR Valve
K20 Engine Control Module The control module contains a microprocessor used to process input data to control outputs. The control module controls a series of actuators to ensure optimal engine performance. The control module does this by reading values from a variety of sensors, interprets the data and adjusts the engine actuators accordingly.

Redirecting the exhaust gas back into the intake system aids in reducing the amount of oxygen that enters the cylinders. This reduces the amount of nitrogen oxide (NOx) that is produced during combustion. The component is actuated by a bidirectional DC motor. Conditions for Running the DTC P0405, P0406 DTC U0651 = Not set Engine = Running Ignition Voltage = Greater than 11 V Frequency the DTC runs = Continuously — After the running conditions are met U0651 Engine = Running Ignition Voltage = Greater than 11 V Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC P0405 Exhaust Gas Recirculation Valve Position Sensor = Short to Ground — For greater than 4 s P0406 Exhaust Gas Recirculation Valve Position Sensor = Short to Voltage — For greater than 4 s U0651 Engine Control Module = Lost Communication with Exhaust Gas Recirculation Valve Position Sensor — For greater than 4 s Actions Taken When the DTC Sets DTCs listed in the DTC Descriptor category = Type A DTC 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 the scan tool parameter: Exhaust Gas Recirculation Valve = 1 to 99% ⇒ If not between 1 and 99% Refer to: Circuit/System Testing ⇓ If between 1 and 99%
  3. 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 is not set
  4. All OK. Circuit/System Testing
  1. Ignition/Vehicle & All vehicle systems » Off
  2. Disconnect the electrical connector: Q14A Exhaust Gas Recirculation Valve 1
  3. Test for less than 10 Ω between the test points: Low Reference circuit terminal 3 & Ground ⇒ If 10 Ω or greater 3.1. Disconnect the electrical connector: K20 Engine Control Module 3.2. Test for less than 2 Ω between the test points: Low Reference circuit terminal 3 @ 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 10 Ω
  4. Ignition » On / Vehicle » In Service Mode
  5. Test for 4.8 to 5.2 V between the test points: 5 V Reference circuit terminal 1 & Low Reference circuit terminal 3 ⇒ If less than 4.8 V 5.1. Ignition/Vehicle » Off 5.2. Disconnect the electrical connector: K20 Engine Control Module 5.3. Test for infinite resistance between the test points: 5 V Reference circuit terminal 1 @ 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: 5 V Reference circuit terminal 1 @ 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 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: 5 V Reference circuit terminal 1 @ 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. Test for 4.9 to 5.3 V between the test points: Serial Data circuit terminal 2 & Ground ⇒ If less than 4.9 V 6.1. Ignition/Vehicle » Off 6.2. Disconnect the electrical connector: K20 Engine Control Module 6.3. Test for infinite resistance between the test points: Serial Data circuit terminal 2 @ Component harness & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇓ If infinite resistance 6.4. Test for infinite resistance between the test points: Serial Data circuit terminal 2 @ Component harness & Low Reference circuit terminal 3 @ Component harness ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇓ If infinite resistance 6.5. Test for less than 2 Ω between the test points: Serial Data circuit terminal 2 @ 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 5.3 V 6.1. Ignition/Vehicle » Off 6.2. Disconnect the 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: Serial Data circuit terminal 2 @ 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 4.9 and 5.3 V
  7. Test or replace the component: Q14A Exhaust Gas Recirculation Valve 1 Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Exhaust Gas Recirculation Valve Replacement - Exhaust Manifold For control module replacement, programming, and setup refer to: Control Module References Additional Procedures