P25C5
Reductant Injection Valve Control Circuit LowP25C5 is a generic OBD-II powertrain diagnostic trouble code: Reductant Injection Valve Control Circuit Low. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P25C5 means
P25C5 is set when the ECM/PCM detects that the control circuit for the reductant (DEF) injection valve (dosing injector) is pulled lower than expected, indicating a short to ground or an excessively low-resistance condition in the circuit. The dosing injector is a solenoid-operated valve that precisely meters urea solution into the exhaust stream upstream of the SCR catalyst.
The ECM drives the injector with a pulse-width-modulated signal and monitors the circuit current or voltage feedback. A short to ground on the signal or power side of the solenoid circuit causes the ECM to detect a low-circuit condition and log P25C5. This typically disables the injector output to protect the driver circuit from overcurrent damage.
With the dosing injector disabled, the SCR system cannot reduce NOx and the vehicle will accumulate NOx-related faults. The fault is most commonly found in the injector wiring harness, particularly in areas exposed to exhaust heat and vibration. A failed injector solenoid with an internal short is also a common cause.
Common causes
Most-frequently reported root causes when P25C5 is logged.
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1
Short to ground in the reductant injection valve signal or power supply wire.
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2
Damaged or chafed wiring harness near the injector due to exhaust heat.
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3
Faulty reductant dosing injector with an internally shorted solenoid winding.
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4
Corroded connector causing a low-resistance path between circuit pins.
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5
ECM output driver circuit failure creating a false low-circuit reading.
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6
Pinched wiring harness against a chassis or exhaust component.
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7
Water intrusion into the injector connector causing a conductive short.
Symptoms drivers notice
How to diagnose P25C5
A typical diagnostic flow when this code is present.
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1
Read all DTCs and record freeze-frame data before any repairs.
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2
Visually inspect the reductant injector wiring harness for chafing, melting, or physical damage near hot exhaust components.
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3
Disconnect the injector connector and measure resistance of the solenoid winding; an out-of-specification low value indicates an internal injector short.
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4
With the injector disconnected, check the harness-side connector for shorts to ground using a multimeter.
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5
Inspect the connector pins for corrosion, pushed-back terminals, or moisture intrusion.
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6
If harness and connector are clean, reconnect and use a scan tool to command the injector while monitoring current; excess current confirms an internal short.
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7
Replace the dosing injector if an internal short is confirmed after harness checks pass.
Vehicles where we've handled P25C5
Platforms in our catalogue with confirmed P25C5 coverage.
Related powertrain codes
Frequently asked questions
Will P25C5 cause a derate immediately?
Immediate derate depends on the vehicle calibration, but SCR dosing will be disabled, leading to NOx faults that can eventually trigger a derate after multiple drive cycles.
Can the ECM be damaged by a shorted injector?
Modern ECMs have over-current protection, but a persistent hard short can stress the driver circuit. Rectify the fault promptly to protect the ECM.
Is the dosing injector the same as the DEF pump?
No. The pump pressurizes the DEF supply, while the dosing injector is a separate solenoid valve that meters the pressurized fluid into the exhaust. They are distinct components.
How do I locate the injector on the vehicle?
The dosing injector is mounted on the exhaust pipe upstream of the SCR catalyst, typically after the diesel particulate filter. Its exact location varies by vehicle layout.
Disabling P25C5 in software
RaceTune can permanently disable P25C5 — 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.
ECUs with a P25C5 disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC17C50 verified 1 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.
Got P25C5 in your scan?
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