Diesel Trouble Codes

P0090 — Fuel Pressure Regulator Control Circuit (5.9 Cummins Common Rail)

Fuel Pressure Regulator Control Circuit

Updated September 2, 2026

What it means

The ECM has detected an electrical fault in the circuit that controls the fuel pressure regulator on this platform. On the 5.9L Cummins Common Rail 2003-2007 ISB this is the Fuel Control Actuator (FCA/MPROP) control circuit on the Bosch CP3 pump. Code P0090 applies to this platform as FCA/MPROP control circuit fault.1

Most likely causes

  1. FCA/MPROP electrical fault or internal failure — The FCA/MPROP is the fuel pressure regulator on the CP3 pump inlet; an open/short or failed actuator can set P0090. Platform has Bosch CP3 pump feeding a common rail with a rail pressure sensor, a fuel control actuator (FCA / MPROP) on the pump inlet, and a mechanical fuel rail pressure relief / pressure-limiting valve on the rail. Rail-pressure codes P0087/P0088 and FCA codes P0090 apply here.2
  2. Wiring/connector damage to FCA control circuit — Chafed, corroded or loose wiring/connectors between ECM and FCA can cause circuit fault detection. Platform has Bosch CP3 pump feeding a common rail with a rail pressure sensor, a fuel control actuator (FCA / MPROP) on the pump inlet.2
  3. ECM driver fault for FCA control — Internal ECM output driver issue for the FCA control circuit can trigger P0090. Generic definition: The engine control module has detected an electrical fault in the circuit that controls the fuel pressure regulator.1

How to diagnose

  1. Verify code P0090 is present and check freeze frame for conditions. Code P0090 applies to this platform as FCA/MPROP control circuit fault.
  2. Inspect FCA/MPROP connector and wiring for corrosion, chafing, pin damage; check harness routing near hot/exhaust components. Platform has fuel control actuator (FCA / MPROP) on the pump inlet.
  3. Check FCA control circuit continuity and isolation to ground/power per service info; look for opens/shorts. Generic definition: The engine control module has detected an electrical fault in the circuit that controls the fuel pressure regulator.
  4. Monitor rail pressure sensor data and commanded vs actual rail pressure with scan tool to confirm regulator control is affected; platform has rail pressure sensor with Bosch CP3 pump.
  5. If wiring and FCA check good, evaluate ECM output/driver for FCA circuit. Generic definition: The engine control module has detected an electrical fault in the circuit that controls the fuel pressure regulator.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by region and shop; FCA/MPROP replacement and wiring repair costs differ. No fixed pricing provided.

When to see a pro

If diagnosis points to ECM driver failure or intermittent wiring faults that require harness repair or ECM evaluation, have a qualified diesel technician perform testing and repair. Do not attempt high-pressure fuel system disassembly. Platform has Bosch CP3 high-pressure pump feeding a common rail.

Sources

  1. Curated DTC seed — 5.9 Cummins Common Rail (curated) ↩︎ ↩︎

  2. Curated DTC seed — 5.9 Cummins Common Rail (curated) ↩︎ ↩︎