Diesel Trouble Codes

P0090 — Fuel Pressure Regulator Control Circuit (6.7 Cummins (SCR / DEF))

P0090 is an electrical fault detected by the ECM in the circuit that controls the fuel pressure regulator on 6.7L Cummins SCR/DEF trucks. The platform uses a…

Updated September 2, 2026

What it means

The ECM has detected an electrical fault in the circuit that controls the fuel pressure regulator. Generic definition: the engine control module has detected an electrical fault in the circuit that controls the fuel pressure regulator. On this platform the regulator control is via the FCA/MPROP on the CP3/CP4.2 pump, with rail pressure feedback from the rail pressure sensor and a mechanical rail pressure relief/pressure-limiting valve.123

Most likely causes

  1. Open or short to ground/power in FCA/MPROP control wiring or connector — Inspect FCA/MPROP harness, pins, and connector for chafing, corrosion, or loose terminals. Check ECM connector and related bulkhead passages for moisture. Verify wiring integrity between ECM and FCA/MPROP. This is an electrical circuit fault per generic definition.1
  2. Faulty fuel control actuator (FCA/MPROP) or internal coil failure — A failed FCA/MPROP can present as an open/short in the control circuit. Electrical testing of the actuator coil resistance and response per service information can identify a failed unit. Platform uses FCA/MPROP for rail pressure control.23
  3. ECM driver fault for fuel pressure regulator control — If wiring and FCA/MPROP test good, the ECM internal driver for the regulator control circuit may be faulty. Confirm with pinout tests and compare to known-good values before condemning ECM.1
  4. Related low-pressure supply issues causing regulator control anomalies — While P0090 is electrical, low supply pressure from the in-tank electric supply pump can cause abnormal regulator operation and related codes. Platform has in-tank electric supply pump.23

How to diagnose

  1. Verify code and freeze frame; confirm P0090 is present and not accompanied by rail pressure performance codes.
  2. Visually inspect FCA/MPROP connector and wiring harness for damage, oil intrusion, or chafing; check ECM connectors.
  3. Measure FCA/MPROP control circuit resistance and isolation to ground/power per service specs; inspect for opens/shorts.
  4. Check FCA/MPROP coil resistance and compare to spec; perform commanded activation test with scan tool if supported.
  5. Inspect in-tank supply pump electrical connections and verify low-pressure supply is within spec to rule out contributing issues.
  6. If wiring and actuator test normal, perform ECM pinout tests for the regulator control driver; evaluate ECM as last step.

Parts and tools you may need

Rough cost and difficulty

Electrical diagnosis is labor-intensive; FCA/MPROP replacement cost varies by model year and parts source. ECM replacement is high cost and should be confirmed before replacement.

When to see a pro

If wiring tests normal but the circuit fault persists, or if ECM driver testing is required, have a qualified diesel technician perform pinout and ECM evaluation. Do not attempt high-pressure fuel system disassembly for an electrical code.

Sources

  1. Curated DTC seed — 6.7 Cummins (SCR / DEF) (curated) ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — 6.7 Cummins (SCR / DEF) (curated) ↩︎ ↩︎ ↩︎

  3. Curated DTC seed — 6.7 Cummins (SCR / DEF) (curated) ↩︎ ↩︎ ↩︎