GM Service Manual Online
For 1990-2009 cars only

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.

DTC Descriptor

DTC B3621: Head-Up Display (HUD) Information Down Switch

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

HUD Information Down Switch Signal Circuit

B3620

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HUD Switch Ground Circuit

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Circuit/System Description

The head-up display (HUD) information down switch is used to vertically adjust the HUD image on the windshield to accommodate various vehicle operator heights. The HUD monitors the information down switch signal circuit in order to adjust image positions. When the HUD information down switch is depressed and the ignition is in the RUN position, the switch signal to the HUD is low.

Conditions for Running the DTC

The ignition is in RUN.

Conditions for Setting the DTC

The HUD detects that the HUD information down switch signal circuit is low for greater than 60 seconds.

Action Taken When the DTC Sets

The HUD ignores the malfunctioning switch circuit.

Conditions for Clearing the DTC

    • The DTC becomes history when the conditions for setting the DTC are no longer present.
    • The history DTC clears after 40 malfunction-free warm-up cycles.

Reference Information

Schematic Reference

Head Up Display Schematics

Connector End View Reference

    •  Displays and Gages Connector End Views
    •  Inline Harness Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Scan Tool Data List

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the HUD switch.
  2. Test for less than 1.0 ohm of resistance between the HUD switch ground circuit terminal F and ground.
  3. If greater than 1.0 ohm, test the HUD switch ground circuit terminal F for an open/high resistance.
  4. Ignition ON, verify the scan tool Adjust Display Down Switch parameter is Inactive.
  5. If not Inactive, test the image down switch signal circuit terminal K for a short to ground. If the circuit tests normal, replace the HUD.
  6. Install a 3A fused jumper wire between the image down switch signal circuit terminal K and ground. Verify the scan tool Adjust Display Down Switch parameter is Active.
  7. If not Active, test the image down switch signal circuit terminal K for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HUD.
  8. If all circuits test normal, test or replace the HUD switch.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Control Module References
    •  Head Up Display Switch Replacement