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Severity: Moderate Code type: Generic (all makes)

P0275 Code: Cylinder 5 Contribution/Balance

The fuel correction for cylinder 5 is past its limit. Only engines with five or more cylinders can set it.

Safety first · Consult a professional

  • Fuel vapor is flammable. No smoking or open flames; work outdoors and fix fuel leaks before driving.

At a glance

Severity: 3/5 – Moderate3/5

Severity: Moderate

Meaning
Cylinder 5 Contribution/Balance
System
Fuel & Air Metering · Powertrain
Safe to drive?
With caution
Typical repair cost
$300–$6,500
DIY difficulty
Hard

P0275 tells you the engine computer's per-cylinder fuel trim for cylinder 5 has reached its limit: that cylinder is either too weak to keep up or too strong to be tamed. It only exists on engines with at least five cylinders, which in the US mostly means V8 diesel pickups, the six-cylinder Cummins and the five-cylinder 2.7 CDI that powered the first Sprinter vans. On that Mercedes five-cylinder, cylinder 5 is the rearmost, tucked against the firewall, and its injector is the classic place for a leaking seat washer: combustion gas blows past, bakes into black tar around the injector, loosens the hold-down and eventually changes how the injector sprays. On a Power Stroke 6.7 cylinder 5 is the front cylinder on the driver side, on a 6.0 or 6.4 it's the third on the passenger side, on a Duramax the third on the driver side, and on a Cummins the fifth from the front.

Can I keep driving? You can usually keep driving at a moderate pace, but if you hear a puffing tick or smell exhaust in the cab, have it fixed soon: a leaking injector seat gets worse and the injector can seize in the head, turning a small repair into a big one.

How to read P0275

How to read P0275P10223754
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 2 Fuel & air (injector circuit)
  4. 75 Specific fault

Symptoms

  • Rough idle with a rhythmic puffing or ticking sound from one injector
  • Exhaust smell in the engine bay or inside the cab
  • Black, tar-like buildup around an injector
  • Loss of power, sometimes limp mode under load
  • Harder starting than usual

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Injector 5 worn, dripping or with poor spray 32%
  2. Injector 5 seat washer leaking or hold-down bolt loose, with carbon buildup 22%
  3. Low compression in cylinder 5 14%
  4. Damaged wiring or connector at injector 5 12%
  5. Replacement injector installed without its classification code 10%
  6. Air in the fuel supply 5%
  7. Crankshaft signal disturbed by a damaged reluctor ring 5%

Diagnosis step by step

Diagnostic flow: P02751Locate cylinder 5 on your engine2Look and listen at injector 53Check the hold-down4Read smooth-running values5Leak-off test6Compression check

  1. Locate cylinder 5 on your engine

    Mercedes five-cylinders count from the front, so cylinder 5 is the rearmost at the firewall. On V8 diesels it depends on the numbering: driver-side front on the 6.7 Power Stroke, third on the passenger side of the 6.0 and 6.4, third on the driver side of a Duramax. Cummins numbering runs 1 to 6 from the front.

    Tools: Flashlight

  2. Look and listen at injector 5

    Remove the engine cover and inspect around the injector for black, sticky carbon. With the engine idling, listen for a puffing tick that stops when you stop the engine. Either one points to a leaking seat washer.

    Tools: Flashlight

  3. Check the hold-down

    If the injector hold-down bolt is loose or the clamp has lifted, the seat will keep leaking. The repair uses a new seat washer and usually a new bolt, tightened to the specified torque and angle.

    Tools: Torque wrench

  4. Read smooth-running values

    At warm idle, read the per-cylinder quantity corrections with a scan tool that supports the engine. Cylinder 5 far off with the rest near zero confirms the code; everything scattered points to the fuel supply.

    Tools: OBD-II scanner

  5. Leak-off test

    Disconnect the injector return lines, fit clear tubes and run the engine for a few minutes. An injector 5 that returns much more than the others is leaking internally and needs replacement rather than a new washer.

    Tools: Towels & shallow pan, Gloves

  6. Compression check

    Measure compression through the glow plug bore with a diesel adapter. A cylinder 5 noticeably lower than the rest, especially after a long-ignored seat leak, may have a damaged valve or seat.

    Tools: Compression tester

Where the parts are

Ignition: coils and spark plugs per cylinder – P02751234567
Ignition: coils and spark plugs per cylinder
  1. 1Ignition coil
  2. 2Spark plug
  3. 3Fuel injector
  4. 4Camshaft sensor
  5. 5Crankshaft sensor
  6. 6Engine computer (ECM)
  7. 7Intake manifold

Repair options & costs

RepairDIY?Estimated cost
Reseal injector 5 (washer and bolt) No $300–$800
Extract seized injector No $500–$1,500
Replace injector 5 and code it No $600–$1,300
Replace full injector set No $2,500–$6,500
Cylinder head repair after long-term leak No $2,000–$5,000

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Mercedes-Benz

Mercedes CDI diesels, including the five-cylinder 2.7 in early Sprinter vans, are well known for injector seat leaks that leave black carbon around the injector. Caught early it's a reseal; left for a long time, seized injectors can require heavy extraction work.

Emissions / smog test impact

Depends

Heavier diesel pickups may be exempt from or tested differently in state programs, but wherever an OBD check applies, P0275 with the check engine light on fails it.

Frequently asked questions

My engine has four cylinders. Why does it show P0275?

It shouldn't. Double-check the code with a second scan tool; a misread or a code from a different module is more likely than a real cylinder 5 fault on a four-cylinder engine.

What is the puffing sound near the injector?

Combustion gas escaping past a leaking injector seat washer. Each firing stroke pushes a little out, which you hear as a puff or tick. The same gas causes the tar-like buildup.

Why is the rear injector on the Sprinter so often the problem?

It's the hardest to reach, so small seat leaks there tend to be noticed late. By then the carbon has often glued the injector into the head, which is why early attention saves money.

Is replacing the washer enough?

If the leak-off test and correction values are otherwise normal, often yes. If injector 5 also returns too much fuel, it needs replacing along with the washer.

Sources