Fuel rail pressure too low on Mercedes OM651/OM642 diesel — HP pump shaft wear (Bosch CP4) and fuel contamination.
Mercedes-Benz P0087 — Fuel rail pressure too low on Mercedes OM651/OM642 diesel — HP pump shaft wear (Bosch CP4) and fuel contamination. Typical UK independent garage cost: £600–£6000.
What actually causes P0087 on a Mercedes-Benz
Bosch CP4 high-pressure pumps on OM651/OM642 are sensitive to fuel quality — once they start shedding swarf, contamination spreads through rails and injectors. Catch it early at P0087 and you save the injectors; ignore it and you're £4-6k deep.
Mercedes-Benz engines that log P0087
- OM651 2.1 CDI (C/E/Vito/Sprinter)
- OM642 3.0 V6 CDI (E/ML/GL)
How we diagnose P0087 on a Mercedes-Benz
- Read rail pressure live — sudden drops under load = swarf
- Cut open fuel filter and inspect for glitter
- Check VIN for any goodwill / service campaign coverage
- Quote correctly: full system replacement if contamination confirmed
The common misdiagnosis to avoid
Many garages fit just the HP pump and clear codes — leaves swarf in injectors and rails. The full Bosch remedy is pump + injectors + rails + lines.
Mercedes-Benz P0087 repair cost in the UK
Expect £600–£6000 including parts and labour at an independent garage. Main-dealer quotes on Mercedes-Benz are usually higher for the same job, and the spread exists because the cheap cause and the expensive cause throw the same code — pay for the diagnosis before you pay for parts.
Service campaign / TSB note
Mercedes has issued goodwill on selected OM651 CP4 failures within 7 years/100k — always check.
Bob's workshop tip
OM651 P0087 — never fit just the HP pump. Customers who say 'do the cheap fix' are back in 8 weeks with a £6k bill and an injector quote.
Codes usually seen alongside P0087 on Mercedes-Benz
- P0088
- P0089
Symptoms drivers report with P0087
- Sudden loss of power on the motorway — car drops into limp mode at exactly 2,500 RPM
- Restarts fine after a key-cycle, then relimps under load 20 minutes later
- Hard cold-starting: cranks for 4–6 seconds before catching
- Uneven idle with a diesel-knock 'nail' from cold
- MPG drops 3–7 mpg before the light even comes on
- Metal glitter in the fuel filter housing = CP4 pump has already grenaded
Repairs that clear P0087
- Change the fuel filter and retest
- Measure injector back-leakage into a graduated tube
- Test rail pressure against commanded on live data
- Replace the pressure regulator or metering valve
For the generic, all-makes explanation of this code — meaning, every known cause and UK cost bands — see our P0087 guide.
Reading P0087 on a Mercedes-Benz properly
A generic reader will show P0087 and nothing else. What matters is the freeze-frame data stored with it — engine speed, load, coolant temperature and fuel trims at the moment the fault was logged — plus whether any other module on the Mercedes-Benz has logged something at the same time. Codes rarely arrive alone, and the order they were stored in usually points at which one is the cause and which are the consequences.
Clearing P0087 without fixing it
Erasing the code resets the Mercedes-Benz's readiness monitors as well as the light. The fault returns on the next drive cycle if the cause is still there, and in the meantime the incomplete monitors can stop the car passing an emissions check. After a genuine repair, the car is driven until the relevant monitor completes before it is handed back.
Bob's Mechanical Repairs is an independent garage in Birnam, Dunkeld, Perthshire, with 32 years of Bob's experience on the tools. If P0087 is showing on your Mercedes-Benz, bring any scan results with you — we will read the live data ourselves, confirm which cause it actually is, and price the repair before any work starts.