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
The vehicle may be equipped with sectioned coax. Test each section and replace only the faulty section, not the entire length of coax.
- Ignition OFF, disconnect the GPS and cellular coax cable connector at the VCIM.
- Using the EL-49903-3 kit (EL-49903-5 adapter and EL-49903-4 coax cable), connect the EL-49903 GM OnStar antenna diagnostic tool kit to the VCIM.
- Ignition ON, wait 5 minutes, and then contact the OnStar call center consultant by pressing the blue OnStar button. A call center consultant should answer the call.
- If the unit does not connect to the OnStar Call Center, replace the VCIM.
- Ignition OFF, disconnect the EL-49903
GM OnStar antenna diagnostic tool kit EL-49903 from the VCIM and perform the coax cable test on the coax cable between the VCIM and the radio antenna.
- If the coax cable does not pass the test, replace the coax cable.
- If all circuits test normal, replace the radio antenna.
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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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