You may still drive, but treat it as urgent: an intermittent metering fault can surge, cut power, or stall the engine without warning, which is dangerous in traffic. Get it diagnosed before a long or highway trip. P0255 is a diesel-only powertrain code meaning the control module saw an intermittent (comes-and-goes) fault in the fuel-metering control circuit "A" of an electronically controlled rotary/distributor injection pump — the electric actuator that sets how much fuel the pump delivers. "A" is the primary metering channel and "intermittent" means the signal dropped out or read erratically rather than staying failed.
What P0255 means
On older diesels that use a distributor-type (rotary) injection pump — such as the Bosch VP44, the Stanadyne DS4, or the VW/Audi VE pump — fuel quantity is not fixed mechanically; it is set electrically by a fuel-metering (quantity-control) actuator inside or on the pump, commanded by the PCM or by the pump's own controller (Bosch calls this the PSG). The module drives that actuator and watches a feedback signal that reports the actual metering position against what it commanded. P0255 sets when that primary metering-control circuit, designated "A," behaves correctly most of the time but momentarily drops out, glitches, or reads out of range and then recovers. Because the fault is not constant, the ECM flags it as intermittent rather than as a hard circuit-low, circuit-high, or range fault (P0251–P0254). The practical meaning is that fuel quantity is briefly not being metered the way the module wants — so the engine can surge, stumble, or lose power in bursts. Note that Ford Power Stroke (HEUI unit-injector) engines and any modern common-rail diesel do NOT use this code family; common-rail systems fault the fuel-volume regulator / metering unit with codes such as P0001 or P008x instead, so P0255 points specifically at a rotary/distributor-pump application.
Symptoms
- Intermittent surging or hunting — engine speed rises and falls on its own at idle or cruise as the metering command flickers
- Momentary power loss or hesitation that comes and goes, often felt under load or acceleration and then clears
- Rough, misfire-like running in bursts even though ignition-side misfire codes are not the real cause (a diesel has no spark)
- Hard starting or an occasional no-start / stall, sometimes worse when the pump or its electronics are hot
- Check-engine light that may flicker on and off with the fault, sometimes storing only as pending until it repeats
- Symptoms that appear random and are hard to reproduce — a hallmark of an intermittent electrical or actuator fault
Common causes
- A worn or failing fuel-metering (quantity-control) actuator inside the injection pump that intermittently loses position or draws erratic current
- Chafed, pinched, or heat-damaged wiring in the metering-control "A" harness that briefly opens or shorts, especially near the hot pump/engine
- A corroded, loose, or backed-out connector pin at the pump or PCM, which makes and breaks contact with vibration and heat
- A poor or high-resistance ground for the pump actuator or its controller, causing the command/feedback to drift under load
- A failing pump-mounted controller — the Bosch PSG on a VP44, or a heat-sensitive pump-mounted driver (PMD) on a Stanadyne DS4 pump — that glitches when hot
- Low or unstable supply voltage to the pump electronics (weak battery, bad connections, charging fault) upsetting the metering circuit
- An internal PCM driver or feedback fault for the metering channel (verify wiring, connectors, ground, and the pump controller first — this is least common)
Severity & driving advice
Severity: Moderate — Fuel delivery can drop out unpredictably, causing surging, power loss, or a stall — driveable at times but the intermittent behavior can leave you stranded.
Can I drive? You may still drive, but treat it as urgent: an intermittent metering fault can surge, cut power, or stall the engine without warning, which is dangerous in traffic. Get it diagnosed before a long or highway trip.
Diagnostic approach
- Scan all modules and read freeze-frame — Pull every stored and pending code, not just P0255. Note companion pump codes (P0251 range/performance, P0252 low, P0253 high, P0254) and any low-voltage or communication codes, since they narrow whether the problem is the actuator, the wiring, or the pump controller. Read the freeze frame for engine load, RPM, coolant/fuel temperature, and battery voltage at the moment it set — an intermittent that always sets hot points toward a heat-sensitive controller or connector.
- Inspect the pump harness and connectors under load — Visually and physically check the metering-control wiring from the injection pump back to the PCM: look for chafe against the block or brackets, melted insulation near the exhaust or turbo, corroded pins, and spread or backed-out terminals. Because the fault is intermittent, wiggle-test the connectors and harness with the engine idling and a scan tool graphing the metering command/feedback — a momentary spike or dropout while flexing a specific spot localizes the fault.
- Confirm supply voltage and grounds to the pump electronics — With the key on and the engine running, verify the pump controller/actuator sees a steady supply near system voltage (roughly 12–14 V while running) and that its grounds are clean and tight — measure voltage drop across each ground connection and reject anything more than a few tenths of a volt. Unstable supply or a high-resistance ground makes the metering command wander and will set an intermittent code even when the pump itself is fine.
- Measure the metering actuator circuit — With the connector separated, check the fuel-metering actuator/solenoid for continuity and resistance against the manufacturer's spec and compare cold versus hot if possible, since heat-related failures read normal cold and drift when warm. Also test the control wire end-to-end for continuity (near 0 Ω) and for shorts to ground or to voltage. An out-of-range or heat-sensitive reading implicates the actuator or its wiring rather than the module.
- Watch the metering command versus feedback live — Graph the commanded metering value against the actual/feedback signal on a scan tool through a road test or a heat soak that reproduces the symptom. On a healthy pump the two track closely; a brief divergence, flatline, or dropout as the engine surges captures the intermittent fault in the act and tells you whether the module lost the feedback or the actuator failed to follow the command.
- Evaluate the pump controller (PSG/PMD) and the pump as a unit — If wiring, connectors, grounds, and supply all pass, suspect the pump-mounted electronics. On a Bosch VP44 the integrated PSG controller commonly fails intermittently when hot; on a Stanadyne DS4 the pump-mounted driver (PMD/FSD) is a well-known heat-related intermittent failure and is sometimes relocated to run cooler. Confirm with the maker's pump-test procedure before condemning the complete injection pump, which is the most expensive part.
- Verify the PCM last — Only after the pump, its controller, wiring, connectors, grounds, and supply voltage have all checked good should the PCM's metering driver be suspected. Clear the code, reproduce the operating conditions from the freeze frame, and confirm P0255 does not return before replacing or reprogramming the module.
FAQ
What does the "A" and "intermittent" mean in P0255?
"A" is the primary fuel-metering control channel of the injection pump — the main actuator that sets fuel quantity. "Intermittent" means the circuit works most of the time but momentarily drops out, glitches, or reads out of range and then recovers, instead of failing solidly. That comes-and-goes nature is why the module logs P0255 rather than the steady circuit-low (P0252) or circuit-high (P0253) versions.
Which vehicles actually use P0255?
It applies to diesels with an electronically controlled rotary/distributor injection pump — for example the Bosch VP44 (used on some Cummins 5.9L applications), the Stanadyne DS4 pump, or the VW/Audi VE rotary pump. It does NOT apply to Ford Power Stroke HEUI engines or to any modern common-rail diesel; those systems use fuel-volume-regulator codes such as P0001 or the P008x range instead.
Do I have to replace the whole injection pump?
Not necessarily. P0255 is frequently caused by wiring chafe, a corroded connector, a bad ground, low supply voltage, or a heat-sensitive pump controller (the PSG on a VP44 or the pump-mounted driver on a DS4) rather than the pumping mechanism itself. Test the wiring, grounds, supply voltage, and the actuator/controller before condemning the pump, since the complete pump is the most expensive repair.
Why does the fault seem to happen only when the engine is hot?
Heat is a classic trigger for intermittent metering-control faults. Connector pins expand and lose contact, marginal wiring opens, and pump-mounted electronics like the Stanadyne PMD or the Bosch PSG are known to break down as they warm up. Testing or wiggle-testing the circuit after a heat soak, or graphing the command versus feedback while the fault is present, is the reliable way to catch it.
Is it safe to keep driving with P0255?
Short local driving may be possible, but it is risky. An intermittent metering fault can cause sudden surging, power loss, or a stall at any moment, which is hazardous in traffic or on the highway. Because fuel delivery is directly involved and the behavior is unpredictable, get it diagnosed promptly rather than relying on it for long trips.