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Tahoe / Yukon Service Manual

Diagnostic System Check - Trailering

Diagnostic Instructions Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic System Check Instructions provides an overview of each diagnostic step. Continue through the Diagnostic System Check until you are directed to follow a particular diagnostic or repair procedure. Once a repair has been completed, perform the Diagnostic Repair Verification and verify the customer concern has been corrected. The diagnostic procedures within this manual are developed on the assumption that the following areas function as designed: The 12 V battery is fully charged and cables are clean and tight. Refer to: Battery Inspection/Test. Fuses are not open. Refer to: Power Distribution Schematics and Electrical Center Identification Views. Ground circuits for the area of customer concern are clean, tight, and in the correct location. Refer to: Ground Distribution Schematics and Harness Routing Views. All connectors/terminals fully seated in the area of concern. Refer to: Master Electrical Component List. There are no aftermarket devices that affect the operation of the system. Refer to: Checking Aftermarket Accessories. The scan tool powers up. Refer to: Scan Tool Does Not Power Up. Diagnostic Aids The special tool EL-52641 can be used to simulate a connected trailer to the vehicle and aid in diagnosis. If the EL-52641 is not available, a trailer simulator tool can be created. Refer to: Trailering Description and Operation for more information on creating a special tool to simulate a connected trailer. Diagnostic System Check

  1. Ignition ON/Vehicle in Service Mode.
  2. Verify a test light illuminates between terminal E at the X88B Tow Vehicle Electrical Receptacle and ground. ⇒ If the test light does not illuminate. Refer to: Trailer Battery Charging Malfunction. ⇓ If the test light illuminates.
  3. Verify the vehicle is equipped with U1D/UET. ⇒ If the vehicle is not equipped with U1D/UET. Go to step 6. ⇓ If the vehicle is equipped with U1D/UET.
  4. Connect the special tool EL-52641 Trailer Presence Simulator Tool or equivalent simulated trailer lighting tool to the X88B Tow Vehicle Electrical Receptacle, refer to: Trailering Description and Operation for additional information on creating a special tool to simulate a connected trailer.
  5. Verify the scan tool Trailer Connection Status parameter in the K68 Trailer Lamp Control Module is Connected. ⇒If the scan tool parameter is not Connected ⇒ If the scan tool parameter is not Connected. Refer to: Trailer Detection Malfunction. ⇓ If the scan tool parameter is Connected.
  6. Verify the vehicle is equipped with JL1. ⇒ If the vehicle is not equipped with JL1. Go to step 9. ⇓ If the vehicle is equipped with JL1.
  7. Using the + button on the S76 Trailer Brake Control Switch, set the trailer brake gain to maximum gain.
  1. Verify the appropriate light or magnets on the EL-52641 Trailer Presence Simulator Tool or equivalent activate while sliding the S76 Trailer Brake Control Switch manual trailer brake apply lever. ⇒ If the light or magnets do not activate. Refer to: Trailer Brake Malfunction. ⇓ If the light or magnets do activate.
  1. Verify the appropriate lights on the EL-52641 Trailer Presence Simulator Tool or equivalent turn ON and OFF when commanding the following control functions on and off with a scan tool: Left Trailer Turn Signal/Stop Lamp Command. Right Trailer Turn Signal/Stop Lamp Command. Trailer Tail Lamp. Trailer Backup Lamps. ⇒ If one or more lights do not turn on and off. Refer to: Trailer Lamps Malfunction. ⇓ If all of the lights turn on and off.
  2. All OK.