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DTC codes / C06xx · Brakes, steering and suspension / C0603

C0603Active Air Dam Control Circuit High

The C0603 code indicates that the active air dam control module has detected an abnormally high voltage on the circuit that powers or controls the active air dam actuator. In plain English, the computer sees voltage on the control circuit that is higher than expected, which usually points to a short to power, an open ground, or a failed actuator.

SystemChassis
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaBrakes, steering and suspension

Symptoms you may notice

  • The air dam may remain in the deployed (down) position at all times, reducing ground clearance.
  • A warning light or message on the dashboard indicating a fault with the active air dam system.
  • Often no symptoms besides the warning light, as the vehicle remains driveable.
  • The air dam may fail to deploy or retract when commanded, affecting fuel economy at highway speeds.
  • In some cases, the air dam may move erratically or make unusual noises as the actuator struggles.
  • The check engine light may illuminate if the fault affects emissions or aerodynamics monitoring.

Common causes, most likely first

  1. A short to voltage in the control circuit wiring between the module and the actuator.
  2. A faulty active air dam actuator that has an internal short to power.
  3. Corroded or damaged connector pins at the actuator or control module.
  4. An open ground circuit for the actuator, causing the control circuit to see high voltage.
  5. A failed active air dam control module that incorrectly reports high voltage.
  6. Water intrusion into the actuator or connector, leading to electrical shorts.
  7. Aftermarket accessories or improper wiring repairs that introduce a short to power.

How to diagnose and fix it

  1. Use a scan tool to clear the code and verify if it returns immediately; if it does, proceed with circuit testing.
  2. Visually inspect the active air dam actuator and its connector for corrosion, water intrusion, or damaged pins.
  3. Disconnect the actuator and measure voltage on the control circuit with the key on; compare to manufacturer specifications.
  4. Check the ground circuit for the actuator using a multimeter to ensure resistance is within specification.
  5. Perform a wiggle test on the wiring harness while monitoring voltage to detect intermittent shorts.
  6. If the circuit tests good, substitute a known-good actuator and recheck for the code.
  7. If the actuator and wiring are confirmed good, diagnose or replace the active air dam control module as the last step.

When the air dam code misleads

  • A short to voltage in the control circuit is often caused by a chafed wire near the air dam mechanism, which can be missed if only the actuator is replaced.
  • The active air dam system may share power or ground with other body components, so a fault elsewhere can set this code without any air dam issue.
  • Some vehicles will set C0603 if the air dam is physically stuck or obstructed, as the module sees high current feedback interpreted as high voltage.
  • Clearing the code without repairing the underlying circuit will usually result in the code returning after a few drive cycles.
  • A faulty actuator can test good on a bench but fail under load, so always perform a live data check of the actuator command and feedback.

Can I keep driving with C0603?

You can generally continue driving with this code because the active air dam is an aerodynamic aid and does not affect safety or engine operation. Avoid high-speed driving if the air dam is stuck down, as it may reduce fuel economy and could be damaged by road debris.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

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