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Tahoe / Yukon Service Manual

Rear Fog Lamps Malfunction

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. Diagnostic Fault Information

Circuit Circuit Function Short to Ground Open/High Resistance Short to Voltage Signal Performan
7555 Signal B1918 16 1 B1918 17 —
7556 Low Reference — 1 — —
122 Control B19C4 11 1 B19C4 12 —
1450 Ground — 1 — —
1. Rear fog lamp(s) malfunction

Scan Tool Functions K9 Body Control Module – Scan Tool Data

Data Parameter Description
Rear Fog Lamp Command This data parameter will show the rear fog lamp command status as Active/Inactive when the rear fog lamp(s) are turned on/off with the rear fog lamp switch

K219 Lighting Control Module – Scan Tool Control Functions

Control Function Description
Rear Fog Lamp(s) This control function will control the rear fog lamp ON/OFF

Circuit/System Description The S30 Headlamp Switch is used to control the fog lights when equipped (T79/T40). The K9 Body Control Module (BCM) provides 5 V signal circuit 7555 and low reference circuit 7556 to the headlamp switch for backlight dimming and fog light controls. When a dimming/fog light button is pressed, the signal circuit becomes grounded through the appropriate resistor internal to the headlight switch and voltage from the BCM will decrease accordingly. The BCM interprets the signal and responds by sending a serial data message to the K219 Lighting Control Module. The lighting control module responds by applying pulse width modulated (PWM) voltage to the Reference Information Schematic Reference Fog Lights Schematics Connector End View Reference Master Electrical Component List Description and Operation Exterior Lighting Systems Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Scan Tool Reference Control Module References for scan tool information Circuit/System Verification

  1. Ignition ON, headlamps ON.
  1. Verify the scan tool Rear Fog Lamp Command parameter changes between Active and Inactive while commanding the rear fog lamps ON and OFF with the rear fog lamp switch. ⇒ If the parameter does not change Refer to Rear Fog Lamp Switch Malfunction. ⇓ If the parameter changes
  1. Verify the rear fog lamps turn ON and OFF when commanding the Rear Fog Lamp(s) ON and OFF with a scan tool. ⇒ If the rear fog lamps do not turn ON and OFF Refer to Rear Fog Lamps Control Malfunction. ⇓ If the rear fog lamps turn ON and OFF
  2. All OK. Circuit/System Testing Rear Fog Lamp Switch Malfunction
  3. Ignition off, disconnect the connector at the S30 Headlamp Switch.
  4. Verify a test lamp illuminates between low reference terminal 12 and B+. ⇒ If the test lamp does not illuminate 2.1. Test circuit 7556 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found. 2.2. Replace the K9 Body Control Module. ⇓ If the test lamp illuminates
  5. Ignition on/vehicle in service mode, test for 4.8 V – 5.2 V between signal circuit terminal 11 and ground. ⇒ If less than 4.8 V 3.1. Test circuit 7555 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 3.2. Test circuit 7555 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found. 3.3. Replace the K9 Body Control Module. ⇒ If greater than 5.2 V 3.1. Test circuit 7555 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found. 3.2. Replace the K9 Body Control Module. ⇓ If 4.8 V – 5.2 V
  6. Replace the S30 Headlamp Switch. Rear Fog Lamps Control Malfunction
  7. Ignition OFF, disconnect the connector at the appropriate component: E93AL Rear Fascia Lower Signal Lamp – Left E93AR Rear Fascia Lower Signal Lamp – Right
  8. Verify a test lamp illuminates between ground circuit terminal 2 and B+. ⇒ If the test lamp does not illuminate 2.1. Repair the open/high resistance on the ground circuit or ground connection. ⇓ If the test lamp illuminates
  9. Connect a test lamp between control circuit terminal 1 and ground, ignition on.
  10. Verify the test lamp turns on and off when commanding the Rear Fog Lamp(s) on and off with a scan tool. ⇒ If the test lamp is always OFF 4.1. Test circuit 122 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 4.2. Test circuit 122 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 4.3. Replace the K219 Lighting Control Module. ⇒ If the test lamp is always ON 4.1. Test circuit 122 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found. 4.2. Replace the K219 Lighting Control Module. ⇓ If the test lamp turns ON and OFF
  11. Replace the appropriate rear fog lamp. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Lighting Component Replacement Reference Control Module References for BCM replacement, programming, and setup