OBD-II trouble code
P0255: Injection Pump Fuel Metering Control "A" Intermittent (Cam/Rotor/Injector)
On nearly every engine that sets this code, "A" is the only fuel metering control there is. That absence of a second channel to compare against is the defining constraint here — with no live reference available, the vehicle's own record of past events becomes the diagnostic instrument.
Quick facts
- System
- Powertrain
- Category
- Fuel & Air
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $0 – $1,400
- DIY difficulty
- Advanced DIY
Browse every code in P0200–P0299, or start from the full code library.
What does P0255 mean?
Almost every diesel that stores this code has exactly one fuel metering control on its injection pump. There is no second one. That fact is easy to skip past and it is the single most important thing about diagnosing P0255, because it removes the tool a technician would normally reach for first: comparison.
On a circuit with a twin, an intermittent is comparatively tractable. Log both, wait for the event, and the one that misbehaves while the other holds steady has identified itself. Here there is nothing to hold steady. When the metering control drops out there is no parallel trace saying the supply was fine, no second actuator saying the fuel was fine, no other channel to exonerate the shared parts. Every parameter you can see moves together, because everything downstream of this one control moves together. So the question "was it the actuator, the wiring, or the fuel supply?" cannot be settled by looking at a single event on a single channel. It has to be settled some other way.
The other way is history. This code stores a freeze frame each time it sets, and modules keep fault counters and, on many diesels, a small stack of previous occurrences with their conditions. One freeze frame is a snapshot. Three of them are a pattern, and a pattern is what a comparison channel would otherwise have given you. If every recorded event sits at high coolant temperature and moderate load, you are looking at heat opening something — a connection that expands apart, or insulation hardened until warming cracks it. If every event is below freezing and none in summer, the story is fuel gelling or wax at the filter, not electrics. If they cluster at high load with normal temperatures, supply volume is the suspect and the actuator is probably innocent. If they scatter randomly with rough-road driving as the only common factor, terminal tension and vibration are the target. None of those conclusions is available from one occurrence. All of them are available from three.
That reframes what to do with a vehicle whose fault has not returned. Rather than fitting a part and hoping, get the vehicle instrumented and back on the road, and treat the next occurrence as data you are collecting rather than as a failure of the repair. Ask the owner for the date, the weather, the road and what the engine was doing. Written down beside the module's own freeze frames, that record converges on a cause faster than any amount of probing at a circuit that is currently working perfectly.
A note on the name, because it misleads people constantly. "(Cam/Rotor/Injector)" is describing the cam ring and rotor inside a rotary distributor injection pump. It is not pointing at the injectors. Everything this code concerns happens at or inside the pump, upstream of any injector, and replacing injectors on the strength of the title is a well-travelled and expensive dead end.
Because "A" is the common channel, it also has something the rarer variants do not: a large installed population and therefore a real body of published experience. Manufacturer service bulletins covering pump harness routing, connector sealing and known-marginal terminals exist for a lot of these engines, and checking them before spending diagnostic hours is genuinely worthwhile. A known pattern on a common engine is the cheapest diagnosis available.
Finally, the safety point, which follows directly from there being only one channel. There is no redundancy. When this control drops out the engine does not run rough on the remaining half — it loses fuelling outright, and it does so without warning on a vehicle that was behaving normally a second earlier. On a diesel that means losing power steering assist and vacuum brake assist at whatever speed you happen to be doing. If there has ever been a stall while moving, the vehicle should not be driven until the fault is found.
Common causes
- Loose or low-tension terminal in the metering actuator connector at the injection pump
- Corrosion in the pump connector that conducts in some conditions and not others
- Heat-hardened insulation on the pump harness that cracks open as the engine reaches temperature
- Chafed wire making and breaking contact against the pump body or a bracket as the engine rocks under torque
- Broken conductor strands inside intact insulation, producing an open only while the harness is moving
- Water that has entered the connector and now conducts or corrodes depending on conditions
- Waxing or gelling fuel in cold weather, restricting supply only below a certain temperature
- Lift or transfer pump output that is marginal and only falls short under peak demand
- Metering actuator sticking occasionally on deposits or wear
- Actuator coil breaking down when hot, reading perfectly normal on a cold resistance check
- Ground connection that carries adequately most of the time and fails under load or vibration
Symptoms
- Check engine light that illuminates and later extinguishes itself, leaving P0255 stored or pending
- Sudden complete loss of fuelling with no warning, followed by normal running after a restart
- Stalling while moving, which on a single-channel pump is the characteristic failure rather than rough running
- Intermittent hard starting with no pattern the owner can predict
- Brief limp mode that clears on the next key cycle
- Momentary surge or hesitation lasting a few seconds
- Events clustering around a particular season, road or temperature
- An occasional puff of black smoke during an episode
- Everything reading entirely normal on a scan tool by the time the vehicle is inspected
- Fuel economy slightly down over a tank despite the engine feeling fine most of the time
Diagnostic steps
- 1.Recognise that there is no second channel to compare against on this engine, so a single event will not tell you which part of the system failed. Plan to build a history instead.
- 2.Extract every freeze frame and fault occurrence the module holds, not just the most recent one, and lay the conditions out side by side.
- 3.Read the pattern across occurrences. All hot means thermal expansion or heat-cracked insulation; all cold means fuel waxing; all high-load means supply volume; scattered with rough roads in common means terminal tension.
- 4.Ask the owner to record date, weather, road surface and engine state for any further episode, since owner-recorded conditions and module freeze frames together are the substitute for a comparison channel.
- 5.Check manufacturer service bulletins early. This is the common channel on a large population of engines, and known harness routing and connector faults are frequently documented.
- 6.Inspect the pump connector by measuring terminal tension against a matching pin rather than judging by eye, and look for corrosion, a displaced seal and evidence of past water intrusion.
- 7.Walk the pump harness for the two intermittent signatures: shiny flattened rub marks, and stiff dark sections where heat has embrittled the insulation.
- 8.Repeat any wiggle testing at full operating temperature with data recording, since a cold workshop test reproduces almost nothing about a thermal fault.
- 9.Measure fuel supply pressure under peak demand rather than at idle, because a marginal lift pump only falls short when volume is asked of it.
- 10.Drain the water separator and assess fuel quality, particularly where the recorded events are cold-weather only.
- 11.Test the pump ground for voltage drop under load and repeat while the harness is being moved.
- 12.Fit a data logger and return the vehicle to service rather than replacing a part speculatively — the next event is worth more than the next component.
Repair cost
$0 – $1,400
The bottom of this range is genuinely zero, because a share of these turn out to be a connector that needed unplugging, cleaning and reseating. Diagnosis is where the money goes and it is higher than on a fault that holds still, typically $150-$350, because building a usable history takes time and sometimes takes the vehicle going back out with a logger fitted. Connector or terminal repair lands at $120-$400. Harness repair for a chafed or heat-damaged section runs $200-$650. A fuel filter, where the recorded events are all cold-weather, is $60-$220. A lift or transfer pump is $250-$900. A fuel control actuator is $220-$900 installed on most engines. On this code specifically, diagnostic time buys more than parts do, because with only one channel there is no cheap way to prove which part failed.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with diesel injection pump / fuel control actuator service preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.