OBD-II Code P0255 — What It Means & How to Fix It

What Does This Error Mean?

P0255 indicates an intermittent fault in the injection pump fuel metering control circuit on Bank A. The signal from the metering unit is cutting in and out rather than failing completely. Intermittent faults are the trickiest to diagnose — they may come and go with temperature or vibration. You may notice occasional rough running, momentary power loss, or a check engine light that appears and disappears. Don't ignore it — intermittent problems usually get worse and eventually become permanent.

Affected Models

All diesel vehicles 1996+
Common in Ford Power Stroke diesels
Common in Dodge Ram Cummins engines
Common in vehicles with high mileage injection pumps
Common in any diesel with an aging wiring harness

Common Causes

Loose or intermittently connecting wiring plug at the injection pump
Cracked wire insulation that shorts or opens under heat or vibration
Intermittently sticking fuel metering solenoid inside the pump
Corroded connector pins making poor contact only some of the time
Injection pump beginning to fail internally with inconsistent output

How to Fix It

Start by thoroughly inspecting the wiring connector at the injection pump. Wiggle it while the engine runs. If the engine stumbles or the code sets, you've found your problem — bad connection.

This wiggle test is a standard mechanic trick for finding intermittent electrical faults.
Inspect the full wiring harness from the ECM to the injection pump. Look for any point where the harness flexes under vibration. Cracked insulation that opens and closes with movement is a classic intermittent fault.

Pay attention to areas near exhaust heat or sharp edges that could cause gradual insulation wear.
Clean and re-seat the connector at the injection pump. Apply fresh dielectric grease to the pins and ensure the locking tab clicks fully into place. A half-seated connector causes intermittent contact.

Sometimes this simple step resolves the issue completely.
Replace the fuel filter if it hasn't been done recently. An intermittently clogging or fluctuating fuel supply can trigger intermittent metering faults without a hard electrical failure.

Diesel fuel filters are inexpensive insurance against pump problems.
If you can't reproduce the fault, have a diesel shop drive the vehicle with a live scanner connected to monitor injection pump data in real time. Catching the fault live is the only reliable way to diagnose intermittent codes.

Some shops will loan you a data logger to capture the fault during normal daily driving.

When to Call a Professional

Intermittent codes are especially challenging to fix without a diesel specialist. They often don't show up during a static inspection — the fault only appears when driving. A good diesel shop can monitor live injection data while driving to catch the fault in action. Don't let a shop charge you for a pump replacement without catching the fault first — it may be just a wire or connector.

Frequently Asked Questions

Why does my check engine light come on and then go away with P0255?

Because it's an intermittent fault — the problem isn't always present. When the connection or solenoid works normally, no fault is detected and the light turns off. When conditions (heat, vibration, worn contacts) cause the fault to recur, the light comes back. Intermittent faults usually get worse over time and eventually become permanent.

Is P0255 the same as P0251?

Similar, but not identical. P0251 means the metering control circuit has a malfunction (could be permanent). P0255 specifically indicates an intermittent fault — the system detected the problem was not always present. Both relate to the same Bank A metering circuit, but P0255 means the fault comes and goes.

How hard is P0255 to diagnose?

Intermittent faults are among the hardest to diagnose in any vehicle. If you can't reproduce the fault during a shop visit, the technician has nothing to test. Keeping a log of when the light appears (cold starts, hard acceleration, hot weather) helps the tech narrow it down. Some faults only appear after hundreds of miles — be patient with the diagnosis process.