P05D9

Code

Generic P — Powertrain

PCV Regulator Valve Control Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 21 EN: 41 RU: 25

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Page language: EN

Causes

Short to ground on the PCV regulator valve control wire
Open or high-resistance circuit between PCM and PCV regulator valve
Failed PCV regulator valve (internal coil/driver fault)
Poor or corroded connector/pins at the valve or PCM
Blown fuse or loss of supply/ground for the valve circuit
PCM/ECM driver failure

Symptoms

Check Engine Light (MIL) illuminated
Rough idle, hesitation, or poor engine performance
High or fluctuating idle speed
Increased oil consumption or blow-by symptoms
Elevated hydrocarbon emissions / failed emissions test
Possible vacuum leak symptoms (lean codes, surging)

What to check

Retrieve DTC and freeze frame data with a scan tool; note operating conditions when code set
Visual inspection of PCV valve, wiring harness, and connectors for damage, corrosion, or pin push-out
Check related fuses and power/ground at the valve connector with ignition ON
Backprobe the valve connector to measure control signal voltage and compare to expected (see signal parameters)
Measure coil resistance of the PCV regulator valve (bench or in-situ) and compare to service spec
Check continuity and for shorts to ground between the valve control pin and PCM

Signal parameters

Supply: battery voltage (approx. 11–14.5 V) to the valve power pin when circuit uses a switched supply
Control: PCM typically modulates the valve with a variable voltage or PWM duty cycle (0–100% duty, 0–12 V swing depending on design)
Coil resistance: typically in the tens of ohms for solenoid-style PCV regulators; consult vehicle service manual for exact ohms
Current draw: usually low (hundreds of mA); large current or open circuit indicates a fault
Behavior: commanded duty/voltage should vary with engine load/RPM; a constant low/no-voltage on the control line is abnormal

Diagnostic algorithm

Record codes and freeze-frame. Confirm P05D9 is current and note conditions when stored.
Perform visual inspection of PCV valve, vacuum lines, connector, and wiring for damage, oil contamination, or corrosion.
With ignition ON (engine OFF), check for proper supply voltage and ground at the valve connector. Replace blown fuses or restore missing power/ground before further testing.
Backprobe the control pin with a multimeter or oscilloscope. With engine running or while commanding the valve with a scan tool, verify the PCM is producing a control signal (voltage swing or PWM). If the PCM is commanding but the line is low, suspect a short to ground or a heavy load.
Measure resistance of the PCV valve coil. If open or out-of-spec, replace the valve.
Check continuity from the valve control pin to the PCM pin. Look for shorts to ground or other circuits. Repair damaged wiring or connectors as necessary.
If wiring and valve test good but control line remains low when PCM commands, test/replace PCM driver only after confirming wiring and valve integrity.
Clear codes, perform a test drive or reproduce operating conditions, and verify the code does not return.

Likely causes

Short to ground in control wire (most likely)
Damaged connector at PCV regulator valve
Failed PCV regulator valve coil
Blown fuse or missing power/ground to the circuit
PCM output driver fault (least common)

Fault status

⚠️ Status

PCM detected low voltage on the PCV regulator valve control circuit. The control line voltage stayed below the expected threshold while the PCM attempted to command the valve. Code set when the condition persists for the required detection cycles.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours