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Tahoe / Yukon Service Manual

DTC U3018, U3019, or U3501-U3588

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 U3018 Control Module Input Power Circuit 1/2 Correlation DTC U3501 Control Module Input Power 1 Circuit Low Voltage DTC U3502 Control Module Input Power 1 Circuit High Voltage DTC U3505 Control Module Input Power 2 Circuit Low Voltage DTC U3506 Control Module Input Power 2 Circuit High Voltage DTC U3509 Control Module Input Power 3 Circuit Low Voltage DTC U350A Control Module Input Power 3 Circuit High Voltage DTC U3588 Control Module Input Power 4 Circuit Low Voltage Symptom Byte Information: Symptom Byte List Circuit/System Description The control module monitors the system voltage to ensure that it stays within the proper range. Conditions for Running the DTC Ignition = On or Propulsion Active. Conditions for Setting the DTC Control Module Voltage = Less than 9 V or Greater than 15 V — For greater than 5 s Actions Taken When the DTC Sets A message and/or warning indicator may be displayed to the driver. Control Module = May be disabled Conditions for Clearing the DTC System Voltage = 9 to 15 V Diagnostic Aids An open fuse that supplies an input voltage to the module can cause the DTC to set. If an open fuse that supplies voltage to the module is found it is likely to be caused by a short to ground on the output circuits from the module and is not likely to be the module itself. Do not replace the module before isolating all output circuits first. Use the schematics to identify the items/configurations listed below: – Control modules the vehicle is equipped with – The control module’s B+, ignition, and ground circuits – The control module’s circuit terminals and connectors A low or high voltage DTC set in multiple modules may indicate a concern with the charging system. A possible cause for DTCs regarding high system voltage could be overcharging with a battery charger or jump starting. Reference Information Schematic Reference Starting and Charging Schematics Control Module References 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. Vehicle Off all systems off.
  1. Test for 12.4 to 12.8 V between the test points: Battery Positive Post & Battery Negative Post ⇒ If not between 12.4 and 12.8 V Refer to: Battery Inspection/Test ⇓ If between 12.4 and 12.8 V
  2. Propulsion Active— For greater than 15 s
  3. Accessories » Off
  4. Test for 13.4 to 15 V between the test points: Battery Positive Post & Battery Negative Post ⇒ If not between 13.4 and 15 V Refer to: Charging System Test ⇓ If between 13.4 and 15 V
  5. Verify the scan tool parameter: Battery Voltage @ Appropriate control module. = Within 1 V of the battery voltage ⇒ If not within 1 V of each other Refer to: Circuit/System Testing ⇓ If within 1 V of each other
  6. Verify the scan tool parameter: Ignition Voltage @ Control Module = Within 1 V of the battery voltage ⇒ If not within 1 V of each other Refer to: Circuit/System Testing ⇓ If within 1 V of each other
  7. All OK. Circuit/System Testing
  1. Vehicle Off all systems Off.
  2. Disconnect the electrical connector: Appropriate control module.
  3. Test for less than 10 Ω between the test points: Each ground circuit terminal & Ground ⇒ If 10 Ω or greater 3.1. Disconnect the ground connection: Ground terminal 3.2. Test for less than 2 Ω between the test points: Ground circuit terminal @ Control module harness & The other end of the circuit ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Repair the open/high resistance in the ground connection. ⇓ If less than 10 Ω
  4. Verify a test lamp turns On between the test points: Each B+ circuit terminal & Ground ⇒ If the test lamp does not turn On and the circuit fuse is OK 4.1. Remove » Test Lamp 4.2. Test for less than 2 Ω between the test points: B+ circuit terminal @ Control module harness & Output terminal @ Fuse ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Verify the fuse is OK and there is voltage at the fuse. ⇒ If the test lamp does not turn On and the circuit fuse is open 4.1. Remove » Test Lamp 4.2. Test for infinite resistance between the test points: B+ circuit terminal @ Control module harness & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇒ If infinite resistance » Replace the component: Control Module ⇓ If the test lamp turns On
  5. Vehicle » In Service Mode
  6. Verify a test lamp turns On between the test points: Each ignition circuit terminal & Ground ⇒ If the test lamp does not turn On and the circuit fuse is OK 6.1. Ignition/Vehicle » Off & Remove » Test lamp 6.2. Test for less than 2 Ω between the test points: Ignition circuit terminal @ Control module harness & Output terminal @ Fuse ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Verify the fuse is OK and there is voltage at the fuse. ⇒ If the test lamp does not turn On and the circuit fuse is open 6.1. Ignition/Vehicle » Off & Remove » Test lamp 6.2. Test for infinite resistance between the test points: Ignition circuit terminal @ Control module harness & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇒ If infinite resistance » Replace the component: Control Module ⇓ If the test lamp turns On
  7. Replace the component: Control Module Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Control Module References for control module replacement, programming and setup.