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.
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
- 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
- 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
- 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
- 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
- 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
- High-pressure fuel system leak (injector return, rail fittings, high-pressure lines). — External or internal leakage reduces achievable rail pressure, especially under load.1
- Restricted fuel filter or contaminated fuel. — Increased restriction on the low side reduces pump inlet flow, limiting high-pressure output.2
How to diagnose
- Verify freeze frame and repeat the fault under controlled load; confirm actual vs commanded rail pressure.
- Check low-side supply pressure/volume to rule out in-tank pump/filter restriction (P008A context).
- Inspect fuel quality and filter condition; replace filter per service interval.
- Monitor rail pressure sensor data and FCA/MPROP command; compare to expected values.
- Perform a controlled leak test of the high-pressure system and inspect the mechanical rail pressure relief/pressure-limiting valve for sticking/leakage.
- 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
- Scan tool with live data for rail pressure actual/commanded, FCA duty, low-side pressure
- Fuel pressure test kit – low side
- Digital multimeter/oscilloscope for sensor and actuator circuits
- Fuel filter and water separator service kit
- Clean lint-free shop towels and approved diesel fuel
Tools you’ll need
- digital multimeter — Verifies rail pressure sensor voltage and FCA/MPROP control circuit integrity to rule out electrical faults causing low pressure reports.
- fuel pressure gauge — Measures low-side supply pressure and volume to confirm in-tank pump and filter can support high-pressure pump demand.
- OBD-II scan tool — Reads freeze frame, actual vs commanded rail pressure, and FCA duty cycle to pinpoint whether pressure is truly low or sensor reported.
- rail pressure test adapter — Allows direct mechanical verification of rail pressure against sensor data and detection of relief valve leakage under load.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| Rail pressure relief valve | $50–$200 | 0.5–1.5 hrs | DIY with tools and a manual |
| Fuel pressure control valve (FCA/regulator) | $100–$400 | 0.5–2 hrs | DIY with tools and a manual |
| Lift pump / fuel transfer pump | $100–$400 | 1–3 hrs | DIY with tools and a manual |
| High-pressure fuel pump | $700–$2,000 | 3–6 hrs | Shop |
Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.
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.
Check for recalls
Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.
Sources
Repair videos: P0087 on the 6.7 Cummins '13+
Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.
Spotted an error, or something missing? Tell us
Run a 6.7 Cummins (SCR / DEF)? This goes straight to the editor — it is not published.