Diesel Trouble Codes

P0087 — Fuel Rail/System Pressure Too Low (5.9 Cummins Common Rail)

Measured fuel rail pressure is below the PCM's commanded value on the 5.9L Cummins Common Rail 2003-2007 ISB.

Updated September 2, 2026

What it means

The PCM commands rail pressure but the rail pressure sensor reports lower than expected. P0087 is valid for this platform.1

Most likely causes

  1. Low-pressure supply restriction or failure (in-tank lift pump / fuel module, clogged filter, restricted pickup, air ingress). — Insufficient inlet flow to the CP3 causes the high-pressure pump to be unable to build commanded rail pressure.12
  2. Fuel control actuator (FCA/MPROP) performance or electrical fault. — FCA controls CP3 inlet metering; a sticking or electrically faulty FCA can limit pump output. P0090 applies to FCA control circuit on this platform.123
  3. Rail pressure sensor signal error (bias / wiring). — Erroneous low reading from the rail pressure sensor can set P0087 even if mechanical pressure is adequate. P0193 is rail pressure sensor circuit high on this platform.12
  4. High-pressure pump (CP3) wear / internal leakage. — A worn CP3 cannot generate required rail pressure under load.12
  5. Mechanical rail pressure relief / pressure-limiting valve leaking open. — A leaking relief valve bleeds rail pressure back to return.2
  6. Injector return leakage excessive. — Excessive leak-back from one or more Bosch common-rail solenoid injectors reduces net rail pressure. Injector electrical faults show as P0201-P0206; contribution faults as P0263-family. [3,7].24

How to diagnose

  1. Verify code and freeze-frame conditions; confirm P0087 is present and repeatable.
  2. Inspect low-pressure supply: check lift pump operation / fuel module output, filter condition, and for air ingress in supply lines. Low-pressure fuel is supplied by in-tank electric lift pump / fuel module.
  3. Monitor actual vs commanded rail pressure with scan tool under idle and load; note pressure deviation. Generic definition: measured pressure below commanded.
  4. Check rail pressure sensor circuit integrity and reference/return voltages; compare sensor reading to a known-good reference if available. Rail pressure sensor is present on this platform.
  5. Evaluate FCA/MPROP command and response; check FCA electrical circuit for faults (P0090 applies).
  6. Perform high-pressure side leak tests (return flow measurement, injector leak-back assessment) to identify excessive injector return or relief valve leakage. Injectors are Bosch common-rail solenoid type. [3,7]
  7. If pressure remains low with good low-pressure supply and no sensor/electrical faults, suspect CP3 pump performance / internal wear. CP3 feeds the common rail on this platform.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by region and vehicle condition; diagnostic time is required before parts replacement.

When to see a pro

High-pressure fuel systems operate at extreme pressures. If diagnosis points to internal high-pressure pump or rail components, have a qualified diesel technician perform testing and replacement. Do not attempt step-by-step repair of safety-critical high-pressure fuel lines.

Sources

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

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

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

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

Watch a repair

Third-party videos, not ours — for illustration. Confirm anything against the factory service information for your truck.

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