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DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P20A2

P20A2Reductant Purge Control Valve A Circuit Low

P20A2 indicates that the powertrain control module (PCM) has detected a low-voltage condition on the control circuit for the reductant purge control valve 'A', which is part of the diesel exhaust fluid (DEF) system. The PCM expects a certain voltage on the valve's control circuit when commanding it on or off, and a reading below the acceptable threshold triggers this code.

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 (malfunction indicator lamp).
  • Often no symptoms besides the warning light, especially if the valve is stuck closed.
  • Possible reduction in engine power or limp mode if the system detects a fault that affects emissions compliance.
  • A message on the dashboard indicating a DEF system fault or service required.
  • In some cases, the vehicle may enter a speed-limited mode after a certain number of ignition cycles.
  • Rough running or poor fuel economy is unlikely but can occur if the valve affects DEF dosing and subsequent emissions control.

Common causes, most likely first

  1. Faulty reductant purge control valve 'A' (open or shorted internally).
  2. Damaged or corroded wiring or connector at the valve.
  3. Open or short to ground in the control circuit between the PCM and the valve.
  4. Poor electrical connection at the PCM connector.
  5. Failed PCM driver for the purge control valve circuit (rare).
  6. Contamination or blockage in the DEF system causing the valve to draw excessive current and set a low-voltage code.
  7. Aftermarket or incorrect DEF fluid causing valve malfunction.

How to diagnose and fix it

  1. Use a scan tool to verify the code and check for any related codes in the DEF system.
  2. Inspect the wiring harness and connector at the reductant purge control valve for damage, corrosion, or loose pins.
  3. Measure the resistance of the purge control valve and compare to the manufacturer's specification.
  4. Check for battery voltage at the valve connector with the key on and the valve commanded on; also check for a good ground.
  5. Perform a voltage drop test on the control circuit to detect excessive resistance.
  6. If the circuit and valve test good, suspect the PCM; check for technical service bulletins (TSBs) before replacement.
  7. Clear the code and perform a road test to verify the repair, ensuring the monitor runs and the code does not return.

Common Misdiagnosis of P20A2

  • A low-voltage code for the purge control valve often results from a poor ground connection rather than a failed valve, so always check grounds before replacing parts.
  • The reductant purge control valve is sometimes confused with the reductant injector; ensure you are testing the correct component.
  • DEF crystallization can cause the valve to stick and draw high current, setting a low-voltage code; inspect for white crystalline deposits.
  • In some vehicles, a low-voltage code can be set by a weak battery or charging system issue, so verify battery condition first.
  • Aftermarket DEF fluid or contaminated fluid can lead to valve failure and set this code; always use manufacturer-approved DEF.

Can I keep driving with P20A2?

You can generally drive with this code, but avoid long distances or heavy loads until it is repaired, as the vehicle may enter limp mode or fail emissions testing. If the check engine light flashes or performance degrades, stop driving and seek service.

Tools that help

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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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