Fuel and air

P00C9 — Fuel Pressure Regulator Solenoid Supply Voltage Low

Severity: medium Drive with care, to a shop

What P00C9 means

The engine control unit uses a fuel pressure regulator solenoid (control valve) to set rail pressure. P00C9 sets when the voltage on this solenoid's supply circuit is lower than expected. Typical causes are wiring or connector problems, weak system voltage, or a failing solenoid, regulator, or control unit.

Symptoms

  • Check Engine light on
  • Reduced engine power
  • Hesitation or surging when accelerating
  • Poor fuel economy
  • Hard starting or long cranking
  • Rough running or stalling under load

Possible causes

  1. Failed fuel pressure regulator solenoid
  2. Damaged wiring, open circuit, or short to ground
  3. Corroded or loose connector
  4. Weak battery or charging problem causing low voltage
  5. Faulty regulator or pump volume control valve
  6. PCM fault (uncommon)

How to diagnose

  1. Scan for all codes and freeze frame data, and note any other fuel or power supply codes.
  2. Test battery voltage and charging voltage with the engine running.
  3. Inspect the solenoid harness and connector for chafing, heat damage, corrosion, or moisture.
  4. Check supply voltage at the solenoid connector with the ignition on, and test circuit resistance back to the PCM.
  5. Check the related fuse and relay.
  6. Measure the solenoid coil resistance and compare it with the specification.
  7. With a scan tool, compare desired and actual rail pressure at cranking, idle, and under load.
  8. Verify low-pressure supply (fuel pump, filter, lines).

Common fixes

  • Repair wiring or replace the damaged connector
  • Replace the fuel pressure regulator solenoid
  • Fix the battery or charging system fault
  • Replace the regulator or pump control valve if faulty
  • Repair or reprogram the PCM only after other causes are ruled out

Questions and answers

What does P00C9 mean?

The PCM detected low voltage in the supply circuit of the fuel pressure regulator solenoid. Wiring, connectors, system voltage, or the solenoid itself are the usual culprits.

Can I drive with P00C9?

Only briefly and carefully. The engine may lose power or stall, so have it checked as soon as you can.

How much does it cost to fix P00C9?

It depends on the cause. A connector or wire repair is usually inexpensive, while a solenoid or regulator replacement costs more. Diagnose first.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.