A burned-out or faulty traction control warning bulb or LED.; Corroded, loose, or damaged wiring and connectors at the traction control lamp, the instrument cluster, or the traction control module.; A failed traction control module or instrument cluster driver that cannot supply or monitor the lamp circuit properly.; A short to ground or short to voltage in the lamp control wire.; An open circuit in the lamp power or ground circuit.; Water intrusion or physical damage to the lamp housing or circuit board.; Aftermarket accessories or improper wiring tapped into the lamp circuit causing interference.

DTC codes / C04xx · Brakes, steering and suspension / C0402

C0402Traction Control Lamp Circuit

Q: What does code C0402 mean?

Traction Control Lamp Circuit. C0402 indicates that the traction control module has detected a fault in the electrical circuit that illuminates the traction control warning lamp, often called the TC or TCS light. The computer monitors the lamp circuit for expected voltage or current and sets this code when the readings fall outside the normal range, meaning the lamp may not turn on when required or may stay on unexpectedly.

C0402 indicates that the traction control module has detected a fault in the electrical circuit that illuminates the traction control warning lamp, often called the TC or TCS light. The computer monitors the lamp circuit for expected voltage or current and sets this code when the readings fall outside the normal range, meaning the lamp may not turn on when required or may stay on unexpectedly.

SystemChassis

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaBrakes, steering and suspension

Symptoms you may notice

The traction control warning light may not illuminate at all when the ignition is turned on or when the system activates.
The traction control warning light may stay illuminated continuously even when no traction control event is occurring.
The stability control or traction control system may be disabled, and the driver may notice reduced intervention on slippery surfaces.
Often no symptoms besides the warning light, as the lamp circuit fault does not affect the actual traction control function in many cases.
In some vehicles, a chime or message may appear on the driver information center indicating a traction control system fault.
The ABS warning light may also illuminate if the traction control lamp circuit is shared with the ABS module.

Common causes, most likely first

A burned-out or faulty traction control warning bulb or LED.
Corroded, loose, or damaged wiring and connectors at the traction control lamp, the instrument cluster, or the traction control module.
A failed traction control module or instrument cluster driver that cannot supply or monitor the lamp circuit properly.
A short to ground or short to voltage in the lamp control wire.
An open circuit in the lamp power or ground circuit.
Water intrusion or physical damage to the lamp housing or circuit board.
Aftermarket accessories or improper wiring tapped into the lamp circuit causing interference.

How to diagnose and fix it

Verify the traction control warning lamp operates correctly during the instrument cluster self-test at key-on; if it does not, inspect the bulb or LED and replace if faulty.
Check the lamp circuit wiring and connectors for corrosion, looseness, or damage, and repair as needed.
Measure resistance and voltage on the lamp control circuit at the module and at the cluster to identify opens or shorts.
Inspect for aftermarket wiring or accessories that may be interfering with the lamp circuit and remove or correct them.
If the circuit tests good, substitute a known-good traction control module or instrument cluster to isolate the fault.
Clear the code and perform a road test to confirm the repair and ensure the lamp operates correctly under all conditions.
If the fault persists, consult the vehicle-specific service information for pinpoint tests and module programming or replacement procedures.

The lamp circuit fault that fools many technicians

A common misdiagnosis is to replace the traction control module when the actual problem is a simple burned-out bulb or a corroded connector at the lamp, so always start with the lamp itself.
Some vehicles use the same lamp for both traction control and stability control, and a fault in one system can illuminate the other warning light, leading to confusion about which system is failing.
The traction control lamp circuit may be monitored only when the lamp is commanded on, so an intermittent fault may not set the code until the system tries to activate the lamp during a traction event or self-test.
Aftermarket alarms, remote starters, or audio installations that tap into the instrument cluster wiring can disturb the lamp circuit and trigger C0402 without any factory component failure.
On some models, the traction control module communicates the lamp request over a data bus to the instrument cluster, so a communication fault or cluster internal fault can set C0402 even when the wiring between the module and lamp is intact.

Can I keep driving with C0402?

You can generally continue driving with C0402 because the traction control system itself may still function, but the warning lamp may not alert you to a real fault. Avoid relying on the traction control system until the lamp circuit is repaired, and address the issue promptly to ensure you are warned if a more serious fault occurs.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.