Diesel Trouble Codes

P0087 — Fuel Rail/System Pressure Too Low (6.7 Cummins (SCR / DEF))

Measured fuel rail pressure is below the PCM's commanded value on 6.7L Cummins SCR/DEF 2013–present.

Updated September 2, 2026

What it means

The PCM commands a rail pressure target and the rail pressure sensor reports lower than expected pressure. On this platform the high-pressure side is a Bosch CP3 for 2013–2018 and 2021+, CP4.2 for 2019–2020 only, with a rail pressure sensor, fuel control actuator (FCA/MPROP), and a mechanical rail pressure relief/pressure-limiting valve on the rail. Low-side supply is an in-tank electric pump. The code is generic SAE J2012 and Cummins enhanced for this platform.1

Most likely causes

  1. Low-side supply pressure/volume insufficient (in-tank electric supply pump, clogged pickup/strainer, restricted fuel filter). — Insufficient low-pressure feed starves the CP3/CP4.2, limiting high-pressure generation. Diagnose by monitoring low-side pressure/volume per P008A guidance and inspecting supply components.12
  2. High-pressure pump wear or failure (CP3 2013–2018 & 2021+, CP4.2 2019–2020). — Reduced pumping capacity causes rail pressure to fall under load. Compare actual vs commanded rail pressure at idle and load; pump performance is platform-specific to CP3/CP4.2 years.1
  3. Fuel control actuator (FCA/MPROP) performance issue. — FCA regulates high-pressure pump output. A faulty or sticking FCA can under-deliver pressure. Evaluate FCA command vs rail pressure response.1
  4. Rail pressure sensor or wiring fault reporting low pressure. — Erroneous sensor signal can set P0087 without a true pressure loss. Verify sensor voltage/reading against a known-good reference and inspect wiring.1
  5. Mechanical rail pressure relief/pressure-limiting valve stuck open or leaking. — A stuck relief valve bleeds rail pressure. This is a common real cause of P0087/P0088 on this platform.13
  6. High-pressure fuel system leak (injector return, rail fittings, high-pressure lines). — External or internal leakage reduces achievable rail pressure, especially under load.1
  7. Restricted fuel filter or contaminated fuel. — Increased restriction on the low side reduces pump inlet flow, limiting high-pressure output.2

How to diagnose

  1. Verify freeze frame and repeat the fault under controlled load; confirm actual vs commanded rail pressure.
  2. Check low-side supply pressure/volume to rule out in-tank pump/filter restriction (P008A context).
  3. Inspect fuel quality and filter condition; replace filter per service interval.
  4. Monitor rail pressure sensor data and FCA/MPROP command; compare to expected values.
  5. Perform a controlled leak test of the high-pressure system and inspect the mechanical rail pressure relief/pressure-limiting valve for sticking/leakage.
  6. If pressure remains low with good low-side supply, evaluate high-pressure pump performance per model-year pump type (CP3 vs CP4.2).

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by model year, pump type (CP3 vs CP4.2), and whether the issue is low-side supply, FCA, sensor, relief valve, or high-pressure pump. Diagnosis time is included before parts replacement.

When to see a pro

High-pressure fuel systems operate at extreme pressures. If diagnosis points to internal high-pressure pump failure, rail relief valve service, or injector/high-pressure line work, have a qualified diesel technician perform the work. Do not attempt step-by-step repair of safety-critical high-pressure fuel components.

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) ↩︎

Watch a repair

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

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