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DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P2064

P2064Reductant Supply Control Circuit High

P2064 means the engine computer has detected a high-voltage condition on the control circuit for the reductant supply system, which is part of the diesel exhaust fluid (DEF) dosing hardware on diesel vehicles. The computer expects a certain voltage range on the control wire and sees a value above the acceptable threshold, indicating a short to voltage or an open control circuit.

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 message on the dash warning of incorrect DEF quality or a reductant system fault
  • Reduced engine power or limp mode if the fault persists and the system disables dosing
  • Difficulty starting the engine in cold weather if the DEF system is disabled
  • Increased diesel exhaust fluid consumption in some cases before the fault is set

Common causes, most likely first

  1. Damaged or chafed wiring in the reductant supply control circuit, causing a short to voltage
  2. Corroded or loose electrical connector at the reductant supply pump or control module
  3. Failed reductant supply pump or its integrated control electronics
  4. Faulty reductant control module or power supply relay
  5. Water or DEF intrusion into a connector or module, creating a conductive path
  6. Aftermarket accessories or poor previous repairs tapping into the circuit

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data to confirm when and under what conditions P2064 set
  2. Visually inspect the reductant supply pump connector and harness for corrosion, chafing, or signs of fluid intrusion
  3. Disconnect the reductant supply pump and measure voltage on the control circuit with the key on to check for a short to voltage
  4. Check the control circuit for continuity to ground and to battery voltage to rule out an open or shorted wire
  5. Test the reductant supply pump with a bidirectional scan tool to command it on and observe circuit response
  6. If the pump fails to respond correctly and wiring is good, replace the reductant supply pump or control module as diagnosed
  7. Clear codes and perform a road test with the scan tool monitoring reductant supply control circuit voltage to confirm the repair

Don't overlook the DEF pump connector

  • A common cause of P2064 that technicians miss is a partially unseated or corroded connector at the reductant supply pump, which can create a high-voltage condition without any visible damage.
  • The code does not always mean the pump has failed; a short to voltage in the harness from a rubbed wire near the frame rail or exhaust component is just as likely.
  • Aftermarket electrical accessories or poor previous repairs that tap into the reductant circuit can introduce a voltage backfeed that sets this code.
  • A weak or failing battery or charging system can cause erratic voltages on the control circuit, so always verify system voltage stability before condemning components.
  • Some vehicles require a relearn or adaptation reset after replacing the reductant supply pump, and skipping this step can cause the code to return.

Can I keep driving with P2064?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads and long trips because the system may enter limp mode and reduce power. If the check engine light starts flashing or you notice severe power loss, stop driving and seek professional diagnosis.

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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