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DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P20F6

P20F6Reductant Injection Valve Stuck Open (Bank 1 Unit 1)

P20F6 indicates that the powertrain control module has detected a fault in the reductant injection valve for bank 1 unit 1, specifically that the valve is stuck open. The computer monitors the valve's electrical circuit and the resulting pressure or flow changes, and it sets this code when the valve remains open when commanded closed or fails to seal properly.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • A persistent diesel exhaust fluid (DEF) smell from the exhaust system
  • Increased DEF consumption due to continuous injection
  • White or blueish exhaust smoke caused by excess reductant entering the exhaust
  • Possible reduction in engine power or torque as the system enters limp mode
  • Illumination of a separate DEF or emissions system warning message on the dashboard

Common causes, most likely first

  1. Reductant injection valve mechanically stuck open due to debris or crystallization
  2. Failed valve solenoid or internal electrical short causing the valve to remain energized
  3. Corroded or damaged wiring harness connector at the reductant injection valve
  4. Contaminated diesel exhaust fluid (DEF) causing deposits that prevent the valve from closing
  5. Faulty reductant injection valve driver circuit inside the powertrain control module (PCM)
  6. Restricted or kinked reductant supply line holding pressure against the valve
  7. Failed reductant pressure sensor providing false feedback that keeps the valve commanded open

How to diagnose and fix it

  1. Use a scan tool to verify the code and check for any related pending or stored codes in the reductant system
  2. Inspect the reductant injection valve connector and wiring for corrosion, damage, or loose pins
  3. Measure the resistance of the reductant injection valve solenoid and compare it to the manufacturer's specification
  4. Check the reductant supply line for restrictions or kinks that could cause excessive pressure
  5. Remove and inspect the reductant injection valve for crystallization or debris, cleaning or replacing as necessary
  6. Test the reductant pressure sensor signal with a scan tool to ensure it is not skewing the valve command
  7. If all external components test good, follow the manufacturer's diagnostic flow to test the PCM driver circuit or reprogram/replace the PCM

Common misdiagnosis traps for P20F6

  • A stuck-open reductant valve often causes no driveability symptoms beyond the warning light, leading some technicians to clear the code without verifying the valve's actual sealing condition.
  • Crystallized DEF around the valve tip can mimic a failed solenoid, so cleaning the valve and retesting is often more cost-effective than immediate replacement.
  • The PCM may command the valve open based on faulty pressure sensor feedback, so a skewed sensor can set this code even when the valve itself is functioning correctly.
  • Wiring harness chafing near the exhaust or transmission is a frequent hidden cause that is overlooked when only the valve is inspected.
  • This code does not always mean the valve is permanently stuck open; intermittent sticking due to cold DEF or minor debris can set it sporadically, so a thorough road test with live data is essential.

Can I keep driving with P20F6?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads or long trips because continuous DEF injection can damage the exhaust aftertreatment system and may trigger limp mode. If the check engine light begins flashing or the engine loses power, stop driving and seek professional assistance.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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