Faulty PCV regulator valve solenoid with an internal short or open winding; Damaged or disconnected electrical connector at the PCV regulator valve; Chafed, broken, or shorted wire in the control circuit between the valve and the PCM; Corroded or loose terminals at the PCM connector for the affected circuit; Failed PCM driver for the PCV regulator valve control circuit (rare)

DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P05D9

P05D9PCV Regulator Valve Control Circuit Low

Q: What does code P05D9 mean?

PCV Regulator Valve Control Circuit Low. P05D9 indicates that the powertrain control module has detected an abnormally low voltage or current on the control circuit for the positive crankcase ventilation (PCV) regulator valve. This valve is electronically controlled to manage crankcase pressure and ventilation flow, and a low circuit condition means the computer cannot properly command the valve, often due to a short to ground, an open circuit, or a faulty valve.

P05D9 indicates that the powertrain control module has detected an abnormally low voltage or current on the control circuit for the positive crankcase ventilation (PCV) regulator valve. This valve is electronically controlled to manage crankcase pressure and ventilation flow, and a low circuit condition means the computer cannot properly command the valve, often due to a short to ground, an open circuit, or a faulty valve.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Rough idle or unstable engine operation due to improper crankcase ventilation
Increased oil consumption or oil leaks from excessive crankcase pressure
Possible whistling or hissing noises from the engine area
Poor fuel economy or slightly elevated emissions

Common causes, most likely first

Faulty PCV regulator valve solenoid with an internal short or open winding
Damaged or disconnected electrical connector at the PCV regulator valve
Chafed, broken, or shorted wire in the control circuit between the valve and the PCM
Corroded or loose terminals at the PCM connector for the affected circuit
Failed PCM driver for the PCV regulator valve control circuit (rare)

How to diagnose and fix it

Verify the code with a scan tool and inspect the PCV regulator valve connector for tightness and corrosion
Measure resistance across the PCV regulator valve solenoid and compare to manufacturer specifications
Check the control circuit for continuity to ground and for a short to ground using a digital multimeter
Inspect the wiring harness for damage, especially near hot or moving components, and repair as needed
Test the control circuit with a test light or oscilloscope to confirm the PCM is commanding the valve
Replace the PCV regulator valve if it fails electrical tests or if the circuit is intact but the valve does not respond
Clear the code and perform a road test to verify the repair and ensure the code does not return

PCV Regulator Circuit Low: What Technicians Check First

A low circuit code often results from a short to ground in the wiring, not a failed valve, so always inspect the harness before replacing parts.
Some vehicles use a PCV regulator valve that is integrated into the valve cover, making replacement more involved and costly than a stand-alone valve.
A dirty or clogged PCV system can cause the valve to draw excessive current and set a low circuit code, so check for sludge or carbon buildup.
The PCM may set this code if the control circuit is open, which can happen if the connector is unplugged or a wire is broken inside the insulation.
Do not overlook the ground circuit for the PCV valve; a poor ground can mimic a low control circuit and lead to misdiagnosis.

Can I keep driving with P05D9?

You can generally drive the vehicle with this code, but avoid extended idling or heavy load conditions until repaired, as improper crankcase ventilation can lead to oil leaks or increased emissions. Have the fault diagnosed soon to prevent potential engine seal damage.

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.