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.
Circuit/System Testing
Use the schematic to determine which control modules are on the BCM communications enable circuit 19, X3.
- Ignition OFF, disconnect the harness connector at the most easily accessible control module on the K9 BCM communication enable relay control circuit.
- Ignition ON, retest for current DTCs. DTC U2099 should remain current.
- If the DTC becomes history, replace the control module that was just disconnected.
- With the prior control modules disconnected, repeat steps 1 and 2 for each control module on the circuit except the K9 BCM.
- Ignition OFF, disconnect the X3 harness connector at the K9 BCM.
- Test for infinite resistance between the serial data communication enable circuit terminal 19 X3 and ground.
- If less than infinite resistance, repair the communication enable relay control circuit for a short to ground.
- If all circuits tests normal, replace the K9 BCM.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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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.
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