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Home / DTC / C0603 — Active Air Dam Control Circuit High

C0603 — Active Air Dam Control Circuit High

Detailed page for trouble code C0603.

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C0603

Generic C — Chassis

Active Air Dam Control Circuit High

Brand: Generic
Type: C — Chassis
Views: UK: 13 EN: 27 RU: 15
AI status
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Page language: EN

Causes

  • Short to battery voltage on the active air dam control or feedback wire
  • Open or corroded connector or poor terminal contact at actuator or module
  • Damaged or chafed wiring harness (insulation worn, pinched, or exposed)
  • Failed active air dam actuator (motor or internal electronics)
  • Faulty body/control module or internal driver circuit
  • Blown or incorrectly rated fuse or failed relay supplying the circuit

Symptoms

  • Check engine / body / ABS warning lamp or a dedicated message about grille shutter
  • Active air dam stuck open or closed, reduced aerodynamic control
  • Possible change in engine bay temperature management (radiator airflow) or fuel economy
  • Uncommanded movement or non-operation of grille shutters
  • Noise from actuator when commanded or attempts to operate

What to check

  • Read and record the DTC(s) and freeze frame data with a scan tool; note ignition and engine conditions
  • Visually inspect actuator, wiring harness, and connectors for damage, corrosion, or disconnection
  • Check related fuses and relays for proper rating and continuity
  • Backprobe the actuator connector and measure supply and signal voltages with ignition ON, engine OFF
  • Command the air dam open/close using a scan tool while observing connector voltages and actuator response
  • Measure resistance of the actuator motor (with harness disconnected) and compare to spec if available

Signal parameters

  • Supply (battery) voltage on power feed: ~11–14 V with ignition ON
  • Control/driver signal expected: typically a low-side drive or PWM from module; active state often near ground (
  • Circuit-high condition: control/feedback wire measures near battery voltage when it should be low or floating
  • Actuator coil/motor resistance (typical range): a few ohms to a few dozen ohms (consult vehicle service data for exact spec)
  • Current draw when operating: may be up to an amp or several amps depending on actuator design; excessive current suggests mechanical bind or short

Diagnostic algorithm

  1. Confirm the code: retrieve C0603 and any related codes; note freeze frame data and clear codes to see if it returns.
  2. Visual inspection: with ignition OFF, inspect the actuator, harness, and connectors for damage, corrosion, rodent chew, or water intrusion.
  3. Check power/fuse: verify the circuit supply fuse and relay (if applicable) are correct and have continuity.
  4. Backprobe measurements: with ignition ON (engine OFF), backprobe the actuator connector and measure supply voltage and the control/feedback pin. If the control line is at battery voltage when it should be low, suspect a short to power or driver fault.
  5. Command test: use a scan tool to command the shutter open/close while monitoring the wiring voltages and actuator behavior. Note whether the module attempts to switch the line and what voltages appear.
  6. Isolate actuator: disconnect the actuator and recheck the control circuit voltage. If the circuit voltage returns to normal when the actuator is disconnected, the actuator or its shorted internal wiring is likely at fault.
  7. Continuity and short test: with ignition OFF, check continuity between the control wire and battery positive to confirm short-to-voltage. Also check continuity to ground where applicable.
  8. Resistance test: measure actuator motor resistance and compare to the specification. Excessively low resistance can indicate internal short.
  9. Repair wiring/connectors: repair any damaged wiring or corroded terminals, secure harness routing, and replace connector as necessary.
  10. Replace faulty components: if tests point to a failed actuator, replace the air dam actuator. If the control module is proven faulty (and wiring is good), replace or repair the module per manufacturer procedures.
  11. Verify repair: clear codes, perform active tests and road/operation verification to ensure the shutter operates correctly and the code does not return.

Likely causes

  • Shorted harness to constant 12 V (most common with 'circuit high')
  • Corroded connector at the air dam actuator
  • Failed actuator with internal short or stuck high output
  • Control module driver failed and is sourcing voltage incorrectly

Fault status

⚠️ Status
C0603 - Active Air Dam Control Circuit High: control circuit voltage higher than expected (possible short to battery or driver/actuator fault).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

C0600 C0601 C0602 C0604 P0563
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