P00C4
Turbocharger/Supercharger Bypass Valve A Control Circuit HighP00C4 is a generic OBD-II powertrain diagnostic trouble code: Turbocharger/Supercharger Bypass Valve A Control Circuit High. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P00C4 means
P00C4 is logged when the ECM detects that the control circuit voltage for Turbocharger or Supercharger Bypass Valve A is higher than the expected range. Unlike P00C3 (low), a high circuit condition most commonly indicates an open circuit in the wiring, a disconnected connector, or an internally open solenoid coil. When the driver circuit is open, the ECM output pin may float toward its supply rail, which the ECM interprets as a high voltage fault.
The bypass valve is a critical component for managing compressor surge and protecting the turbocharger on throttle lift-off events. If the valve cannot be commanded by the ECM, the system may default to a fixed position, which can result in compressor surge (the characteristic flutter or chatter sound on lift-off), reduced durability of the turbo compressor wheel, and possible boost regulation issues.
Technicians should begin diagnosis by checking the connector and wiring for obvious damage or disconnection. Solenoid coil resistance measurement with the connector unplugged will confirm whether the solenoid is open. If the solenoid and wiring check out, an ECM output driver fault should be considered, though this is significantly less common than wiring or solenoid failure.
Common causes
Most-frequently reported root causes when P00C4 is logged.
-
1
Open circuit in the signal wire between the ECM and the bypass valve solenoid.
-
2
Disconnected or improperly seated connector at the bypass valve solenoid.
-
3
Failed solenoid with an open coil winding.
-
4
Broken wire within the harness that becomes intermittent with engine movement.
-
5
Corrosion on connector terminals increasing resistance to the point of functional open circuit.
-
6
Short to battery voltage on the control wire, overriding the ECM driver output.
Symptoms drivers notice
How to diagnose P00C4
A typical diagnostic flow when this code is present.
-
1
Read and record all stored DTCs and freeze frame data with a scan tool.
-
2
Physically inspect the bypass valve solenoid connector for disconnection, bent pins, or corrosion.
-
3
Disconnect the solenoid and measure coil resistance to check for an open winding.
-
4
Check continuity of the signal wire from the ECM to the solenoid connector to identify any open circuit.
-
5
Inspect the wiring harness routing for breaks or damage, particularly at flex points and heat-exposed areas.
-
6
With wiring confirmed intact, verify ECM output driver function by checking for a commanded voltage change on the signal wire during a solenoid actuator test with a scan tool.
-
7
Replace solenoid or repair wiring as indicated, then clear DTCs and confirm repair under normal driving conditions.
Related powertrain codes
Frequently asked questions
Can P00C4 be triggered by a simple disconnected plug?
Yes. A disconnected solenoid connector is one of the most common causes of P00C4, as it creates an open circuit that the ECM interprets as a high voltage condition.
Does P00C4 affect fuel economy?
Indirectly. If the boost system is compromised, the engine may run sub-optimally, and the ECM may adjust fueling and timing strategies in response, affecting efficiency.
Can I test the solenoid without removing it?
You can measure resistance at the connector with the solenoid disconnected, and you can listen for actuation during a scan tool solenoid test. Full current draw testing typically requires the solenoid to be accessible.
How urgent is P00C4 to repair?
It should be addressed promptly. Continued operation without bypass valve function risks turbocharger compressor damage from repeated surge events, particularly during spirited driving.
Disabling P00C4 in software
RaceTune can permanently disable P00C4 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P00C4 in your scan?
Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.
Upload your file