P0259
Injection Pump Fuel Metering Control B High (Cam/Rotor/Injector)P0259 is a generic OBD-II powertrain diagnostic trouble code: Injection Pump Fuel Metering Control B High (Cam/Rotor/Injector). It is logged by the engine control unit when the fuel/inj monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0259 means
P0259 is set when the ECM detects that the fuel metering control circuit "B" voltage remains persistently high — typically above approximately 4.5–4.8 V when a lower value is expected for the commanded state. In distributor-type diesel injection pumps (Bosch VP44, Stanadyne DS4, Bosch VP on pre-2003 Sprinter OM611), the channel-B metering solenoid control line should modulate between a low and a high voltage as the ECM varies the duty cycle. A stuck-high condition means the solenoid is being fully energised (or the feedback signal is pegged near the 5 V reference) regardless of the ECM's intended command, preventing the ECM from reducing fuel delivery below the point corresponding to 100 % solenoid on-time.
Common causes include an open circuit in the solenoid return (ground) path, which leaves the signal wire floating near the 5 V supply rail; a failed solenoid coil with an internal open that prevents current flow (the output driver then reads back the full supply voltage); or a harness fault where the signal wire contacts the 5 V reference feed. On some ECM architectures an internal driver transistor shorted to the supply rail also produces a permanent high output.
A persistent high-voltage condition often results in the solenoid being commanded to a fixed fuel quantity that the ECM cannot modulate. This commonly manifests as black smoke and over-fuelling at light loads, loss of accurate throttle control, and possible engine damage if sustained. Limp mode may not always activate immediately, but the MIL will be illuminated and the ECM will log the fault.
Common causes
Most-frequently reported root causes when P0259 is logged.
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1
Open circuit in the solenoid ground return path, leaving the signal wire floating near the 5 V reference voltage.
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2
Internal open-circuit failure in the solenoid coil preventing current flow, with the ECM driver reading back the full supply rail.
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3
Harness short to the 5 V reference feed, clamping the channel-B signal at the positive rail.
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4
ECM internal output driver transistor shorted to supply, holding channel-B output permanently high.
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5
Damaged solenoid connector with a bent pin bridging the signal terminal to the 5 V reference terminal.
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6
Corroded ground terminal at the injection pump or ECM causing excessive ground resistance and a floating high reference.
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7
Incorrect solenoid installed (wrong coil resistance) presenting a load the ECM driver interprets as open-circuit.
Symptoms drivers notice
How to diagnose P0259
A typical diagnostic flow when this code is present.
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1
Retrieve freeze-frame and confirm the ECM-logged channel-B voltage is above the high-voltage threshold; verify with a digital multimeter at the solenoid connector to distinguish a true high from an ECM reporting error.
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2
Check solenoid coil resistance at the pump connector with the harness unplugged — an open reading (OL / infinite) confirms an internally open coil, explaining why the driver output floats high.
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3
Inspect the solenoid ground return wire for continuity from the pump connector back to the ECM chassis ground; an open ground return makes the signal wire appear high even with a healthy ECM.
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4
With the ignition on and harness connected, probe the signal wire at the pump connector for voltage; if it reads supply voltage (approximately 12 V or 5 V depending on circuit type) with the ECM commanding a low duty cycle, isolate the fault by unplugging the harness mid-run and re-measuring.
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5
Inspect the pump-side connector for bent pins or pin-to-pin bridging at the signal and 5 V reference terminals; even partial contact causes a clamped-high condition.
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6
If all harness and solenoid checks pass, perform an ECM self-test with a factory-level scan tool to check for internal channel-B driver faults before authorising ECM replacement.
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7
After any repair, clear the code, perform a road test under varying load conditions, and confirm channel-B live voltage modulates correctly with throttle input.
Related powertrain codes
- P0065 — Air Assisted Injector Control Range/Performance
- P0066 — Air Assisted Injector Control Circuit or Circuit Low
- P0067 — Air Assisted Injector Control Circuit High
- P0087 — Fuel Rail/System Pressure - Too Low
- P0088 — Fuel Rail/System Pressure - Too High
- P0089 — Fuel Pressure Regulator 1 Performance
Frequently asked questions
What is the difference between P0258 and P0259?
P0258 is a stuck-low fault — the channel-B signal is near ground regardless of the ECM command, typically caused by a short to ground or a shorted solenoid coil drawing excessive current. P0259 is a stuck-high fault — the signal is near the supply reference regardless of command, typically caused by an open circuit in the solenoid or its ground return. The failure mode and associated diagnostic checks are essentially opposite between the two codes.
Can P0259 cause black smoke?
Yes. If the stuck-high condition holds the metering solenoid at maximum or near-maximum energisation, the pump delivers more fuel than the ECM intends for light-load conditions. The excess fuel cannot fully combust, producing dense black smoke from the exhaust. This is a key field symptom that distinguishes P0259 (over-fuelling) from P0258 (under-fuelling or no-start).
Will the engine run normally between fault events if P0259 is stored but not currently active?
If P0259 is stored as a pending or historical code rather than a currently active code, the fault was intermittent and the channel-B circuit may be operating normally at the moment of inspection. Intermittent open circuits in the ground return are a common cause of this behaviour — the fault appears and clears as the connector flexes with engine vibration. Monitor live data under load and vibration to catch the intermittent condition.
Is pump replacement required for P0259?
Rarely on its own. Most P0259 cases are resolved by repairing an open ground return wire, replacing a corroded connector, or replacing an externally accessible solenoid or actuator. Full pump replacement is warranted only if the solenoid coil is internally open and integrated into the pump body in a way that is not serviceable as a standalone part — which applies mainly to sealed Bosch VP pump variants.
Disabling P0259 in software
RaceTune can permanently disable P0259 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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