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.
Fail-Safe Table
This function is provided by the safe mechanism that assures safe driveability even when the coupling assembly, switch, sensor or its circuit fails. The following table shows the fail safe function for each fail condition of sensor, coupling assembly, switch, 4WD control module or its circuit.
| DTC No. | Trouble Area | Fail-Safe Operation |
|---|---|---|
| C1240 | 4WD control module power supply circuit malfunction | 4WD control module controls the current and fixed the vehicle to 2WD position. |
| C1243 | Internal circuit malfunction of 4WD control module | |
| C1250 | Coupling air temperature sensor open | |
| C1251 | Coupling air temperature sensor short | |
| C1252 | Coupling assembly open | |
| C1253 | Coupling assembly short | |
| C1254 | 2WD/4WD switch malfunction | |
| U0073 | Control module communication bus off | |
| U0100 | Lost communication with ECM | |
| U0101 | Lost communication with TCM | |
| U0121 | Lost communication with ABS/ESP® control module | |
| U0155 | Lost communication with instrument panel cluster (IPC) control module |
NO RELATED
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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.