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DTC codes / P05xx · Vehicle speed, idle control and auxiliary inputs / P05EF

P05EFReductant Pump Supply Voltage Circuit Low

P05EF indicates that the powertrain control module (PCM) has detected a low voltage condition on the supply circuit feeding the reductant pump, which is part of the diesel exhaust fluid (DEF) system. The PCM monitors the voltage on the pump's power feed and sets this code when the signal falls below the expected threshold, typically indicating a short to ground, an open circuit, or a faulty pump.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) on the dashboard.
  • Often no symptoms besides the warning light, especially if the pump is still partially functional.
  • Reduced engine performance or limp mode due to the vehicle's emissions control strategy.
  • A message on the driver information center indicating low DEF or a service emissions system warning.
  • Possible difficulty starting the engine if the DEF system is completely inoperative.
  • Increased DEF consumption or failure to inject DEF, leading to further emissions-related codes.

Common causes, most likely first

  1. A short to ground or open circuit in the wiring harness between the PCM and the reductant pump.
  2. Corroded, loose, or damaged electrical connectors at the pump or PCM.
  3. A failed reductant pump with an internal short or open winding.
  4. Blown fuse or relay supplying power to the reductant pump circuit.
  5. High resistance in the ground circuit for the pump, causing a voltage drop.
  6. A faulty PCM driver for the pump supply circuit, though this is less common.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in the reductant system.
  2. Inspect the reductant pump fuse and relay, replacing them if blown or faulty.
  3. Perform a visual inspection of the wiring harness and connectors for damage, corrosion, or loose pins.
  4. Measure voltage at the pump connector with the key on and engine off; compare to battery voltage to identify a supply issue.
  5. Check the ground circuit for the pump using a voltage drop test to ensure a good connection.
  6. If wiring and connectors are good, test the reductant pump by applying power directly and checking for operation; replace if defective.
  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 Reductant Pump Circuits

  • A low voltage code on the reductant pump supply circuit is frequently caused by a poor ground connection rather than a failed pump, so always perform a voltage drop test on both the power and ground sides.
  • The reductant pump may be commanded off by the PCM under certain conditions, such as low DEF level or extreme temperatures, which can set a low voltage code even when the circuit is intact.
  • Aftermarket electrical accessories or improper previous repairs can introduce resistance or shorts into the reductant pump circuit, leading to this code without any component failure.
  • The PCM may set P05EF if the battery voltage is low during cranking, so check the vehicle's charging system and battery condition before condemning the pump.
  • Replacing the reductant pump without checking the supply voltage can lead to repeat failures if the underlying wiring issue is not addressed.

Can I keep driving with P05EF?

You can usually continue driving with this code, but the vehicle may enter limp mode or fail to start if the DEF system becomes completely inoperative. Avoid long trips or heavy loads until the fault is repaired, and be aware that continued driving may lead to further emissions-related codes and reduced fuel economy.

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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