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Tahoe / Yukon Service Manual

Forward Collision Alert System Malfunction (with UGN)

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. Circuit/System Description For an overview of the forward collision alert system, refer to Active Safety System Description and Operation. Diagnostic Aids The forward collision alert system can be inhibited or disengaged for a number of reasons. These reasons may be a normal function of the vehicle or as a result of action the driver has taken. They also may be because of a fault in a vehicle system. The K124 Image Processing Module has an available scan tool data list that can help identify what may have caused a forward collision alert system inhibit or disengage. The scan tool Front Impact Mitigation History Data list identifies conditions that will cause a forward collision alert system inhibit or disable condition. When attempting to diagnose the system, it is important to discuss with the customer the conditions under which the apparent malfunction occurred. This is critical to help identify those scenarios where the inhibit or disengage is the result of a driver action or normal system response and clarify how the function works. It is also critical to identify when the apparent malfunction occurred when attempting to replicate the condition. The parameters in the scan tool Front Impact Mitigation History Data list can be used to help isolate what is causing an inhibit or disengage condition. The scan tool Front Impact Mitigation History Data list has parameters that identify the last eight causes of an inhibit and the last eight causes of a disengage. For each Front Impact Mitigation History Data parameter, extra information is included in additional parameters: Odometer at First Malfunction, Odometer at Last Malfunction, Diagnostic Status, Malfunction Counter, and Ignition Cycles Since Last Diagnostic Event. The scan tool parameters are a rolling snapshot of the last eight inhibit and disengage reasons, however, if the same condition causes an inhibit or disengage, the reason will not be logged in the next parameter. Instead, the Malfunction Counter parameter will increment and the Odometer at Last Malfunction parameter will update with the most recent odometer value that the condition occurred. When diagnosing an inhibit or disengage concern, especially in the case of an intermittent condition, these parameters are useful in helping determine the cause. Recurring causes will have a larger number in the Malfunction Counter parameter and will likely have a wide variance between the Odometer at First Malfunction and Odometer at Last Malfunction value, indicating the condition has occurred over a period of time driving the vehicle. Certain factors will affect the operation of the forward collision alert system. Forward collision alert is intended to detect vehicles. It is not intended to warn the driver of any objects that are not detected as a vehicle such as animals, signs, guard rails, bridges, construction barrels, or other stationary or slow moving objects. In some cases the B174W Front View Camera - Windshield may inadvertently detect a vehicle that is not in the path ahead or the system may occasionally provide unrealistic alerts. This could occur with a turning vehicle ahead, guard rails, traffic signs, or other stationary objects. This is normal operation and the vehicle does not need service. Forward collision alert warnings will not occur unless the forward collision alert system detects a vehicle ahead. When a vehicle is detected, the vehicle ahead indicator will display green. Vehicles may not be detected on curves, highway exit ramps, or hills, due to poor visibility; or if a vehicle ahead is partially blocked by pedestrians or other objects. Forward collision alert will not detect another vehicle ahead until it is completely in the driving lane. The B174W Front View Camera - Windshield may have trouble functioning under the following scenarios: Dirty windshield glass or obstruction on windshield. This may included dirt, snow, or ice, a tinted windshield, windshield tint strips, or vinyl strips or graphics on the windshield. Additionally, other obstructions such as brush guards or hood deflectors may obstruct view of the B174W  Camera – Windshield and hinder it’s ability to identify objects, vehicles, and lane markings. The B174W Frontview Camera – Windshield is not properly installed. Verify it is snapped into tabs and is secure. Ensure the bracket is in the correct location by comparing to a known good vehicle. This is especially important if the windshield was recently replaced. Some aftermarket windshield may have the B174W Frontview Camera – Windshield in the incorrect location. Improper installation of a replacement windshield may also prevent completion of the learn if the windshield was not centered and leveled in the vehicle’s windshield opening. Driving through snow or fog, or driving directly into the sun. Driving on windy or hilly roads. Reference Information Schematic Reference Driver Assistance Systems 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 Scan Tool Reference Control Module References Circuit/System Verification

  1. Ignition ON.
  2. Verify there are no DTCs set related to the Forward Collision Alert or Lane Keep Assist system ⇒ If any DTCs are set Refer to Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If no DTCs are set
  3. Verify the B174W Front View Camera - Windshield is properly installed. Refer to Diagnostic Aids for details about identifying a properly installed B174W Front View Camera - Windshield. ⇒ If the B174W Front View Camera - Windshield is not properly installed Repair as necessary. ⇓ If the B174W Front View Camera - Windshield is properly installed
  4. Verify the windshield in front of the B174W Front View Camera - Windshield is not blocked. Refer to Diagnostic Aids for details about identifying a blocked B174W Front View Camera - Windshield. ⇒ If the windshield is blocked Repair as necessary. ⇓ If the windshield is not blocked
  5. Drive the vehicle.
  6. Press and release the Adaptive Cruise Control Gap Switch. Verify the adaptive cruise control gap setting on the Driver Information Center Display changes between Far, Medium, and Near with each button press. ⇒ If the gap setting does not change Refer to Adaptive Cruise Control Malfunction. ⇓ If the gap setting changes
  7. A fault is currently not present and may be an intermittent condition. Refer to Diagnostic Aids. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Driver Assistance Systems Component Replacement Reference Control Module References for control module replacement, programming, and setup