P20F5
Reductant Injection Valve Control Circuit - HighP20F5 is a generic OBD-II powertrain diagnostic trouble code: Reductant Injection Valve Control Circuit - High. 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 P20F5 means
P20F5 indicates that the ECM has detected a higher-than-expected voltage on the control circuit of the reductant dosing injector (also called the reductant injection valve). The module monitors the electrical circuit and sets this fault when it senses a short to voltage or an open-circuit condition that pulls the line high, depending on the specific circuit architecture used by the manufacturer.
Electrical faults of this nature are most often caused by chafed or shorted wiring in the engine harness near heat sources or moving components, a failed dosing injector solenoid with internal winding damage, or corrosion at the connector leading to abnormal resistance. Because the reductant circuit is exposed to temperature cycling and reductant spray, connector corrosion is a frequent contributor.
With the dosing injector circuit faulted, the SCR system cannot precisely meter reductant into the exhaust stream. This leads to under-dosing or no-dosing conditions, elevated NOx output, and — on vehicles with regulatory derate logic — progressive torque reduction or kilometre-count-based derates if the fault is not corrected.
Common causes
Most-frequently reported root causes when P20F5 is logged.
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1
Short to voltage in the dosing injector control wiring harness.
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2
Open circuit in the injector solenoid winding causing the pull-down line to float high.
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3
Corroded or contaminated connector at the reductant dosing injector.
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4
Damaged wiring insulation near exhaust heat sources creating an unintended voltage path.
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5
Failed ECM driver circuit for the reductant injector output.
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6
Incorrect aftermarket wiring splice introducing a voltage feed onto the control line.
Symptoms drivers notice
How to diagnose P20F5
A typical diagnostic flow when this code is present.
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1
Record all DTCs and freeze-frame data; note any companion reductant or SCR codes.
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2
Inspect the dosing injector wiring harness from the ECM to the injector for visible damage, chafing against exhaust components, or melted insulation.
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3
Disconnect the dosing injector connector and measure voltage on the control circuit wire with the ignition on; an unexpected supply voltage confirms a short to power.
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4
Measure injector solenoid resistance across the injector terminals and compare to the OEM specification to detect an open winding.
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5
Inspect the connector body and terminals for corrosion, pushed-back pins, or DEF crystal contamination; clean or replace as needed.
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6
If wiring and connector are sound, test the ECM driver output per OEM procedure using a test lamp or oscilloscope during a commanded dosing event.
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7
Replace the dosing injector if the solenoid is out of spec; replace or repair the harness segment if a wiring fault is confirmed.
Vehicles where we've handled P20F5
Platforms in our catalogue with confirmed P20F5 coverage.
Related powertrain codes
- P2000 — NOx Adsorber Efficiency Below Threshold Bank 1
- P2001 — NOx Adsorber Efficiency Below Threshold Bank 2
- P2002 — Diesel Particulate Filter Efficiency Below Threshold Bank 1
- P2003 — Diesel Particulate Filter Efficiency Below Threshold Bank 2
- P2004 — Intake Manifold Runner Control Stuck Open Bank 1
- P2005 — Intake Manifold Runner Control Stuck Open Bank 2
Frequently asked questions
Can DEF fluid cause P20F5?
DEF crystallising inside the connector can create corrosion or bridging between terminals, leading to electrical faults. Inspect and clean the injector connector carefully if DEF contamination is present.
Does P20F5 always mean the injector is bad?
Not necessarily. Wiring shorts, open circuits, and connector corrosion are equally common causes. Always inspect the full circuit before replacing the injector.
How do I tell a short-to-voltage from an open circuit?
With the connector unplugged, measure the voltage on the harness side control wire. A short to power shows battery or ignition voltage; an open circuit typically shows 0 V or the pull-up reference with no load path.
Will the code come back after clearing if I only cleaned the connector?
If cleaning resolved the corrosion fully, the code may not return. However, if the underlying cause is a marginal harness or a failing injector, the fault will recur under heat or vibration.
Disabling P20F5 in software
RaceTune can permanently disable P20F5 — 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 P20F5 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 EDC17CP57 verified 2 software versions
- Bosch EDC17C66 verified 1 software version
- Bosch EDC17C74 verified 1 software version
- Bosch EDC17CP44 verified 1 software version
- Bosch MD1CP004 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 P20F5 in your scan?
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