Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSGMC2021YUKON DENALI, 3.0L ENG VIN T, 4WDREPAIR AND DIAGNOSISACCESSORIES & EQUIPMENTANTI-THEFT SYSTEMSTHEFT DETERRENT SYSTEMDIAGNOSTIC INFORMATION AND PROCEDURESSECURITY INDICATOR MALFUNCTIONCIRCUIT/SYSTEM TESTING
2021 GMC Yukon Denali, 3.0L Eng VIN T, 4WD
Circuit/System Testing
2021 GMC Yukon Denali, 3.0L Eng VIN T, 4WDSECTION Circuit/System Testing
- Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the P18 Door Lock Status Indicator. It may take up to 2 min for all vehicle systems to power down.
- Test for less than 30 Ω between the low reference circuit terminal 30 and ground.
- If 30 Ω or greater
- Ignition OFF, disconnect the harness connector at the K9 Body Control Module.
- Test for less than 2 Ω in the low reference circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, replace the K9 Body Control Module.
- Go to next step: If less than 10 Ω
- Ignition ON, connect a test lamp between the control circuit terminal 12 and ground.
- Verify the test lamp turns ON and OFF when commanding the Security Indicator On and Off with a scan tool.
- If the test lamp is always OFF
- Ignition OFF, disconnect the harness connector at the K9 Body Control Module.
- Test for infinite resistance between the control circuit and ground.
- If less than infinite resistance, repair the short to ground on the circuit.
- Go to next step: If infinite resistance
- Test for less than 2 Ω in the control circuit end to end.
- If 2 Ω or greater, repair the open/high resistance in the circuit.
- If less than 2 Ω, replace the K9 Body Control Module.
- If the test lamp is always ON
- Ignition OFF, disconnect the harness connector at the K9 Body Control Module, ignition ON.
- Test for less than 1 V between the control circuit and ground.
- If 1 V or greater, repair the short to voltage on the circuit.
- If less than 1 V, replace the K9 Body Control Module.
- Go to next step: If the test lamp turns ON and OFF
- Test or replace the P18 Door Lock Status Indicator.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.