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DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P208D

P208DReductant Pump A Control Circuit High

P208D means the engine control module has detected an abnormally high voltage on the control circuit for the reductant pump, which is the pump that moves diesel exhaust fluid from the tank to the dosing injector in a selective catalytic reduction system. The high voltage reading tells the module that the circuit is likely shorted to power, open, or that the pump's internal electronics are drawing no current when commanded.

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 driver information message warning that the reductant system is malfunctioning or that the vehicle will soon be speed-limited
  • Reduced engine power or a limp-home mode once the fault is active for several drive cycles
  • The reductant pump may be heard running continuously or not at all when the key is turned on
  • Increased diesel exhaust fluid consumption or a sudden drop in the tank level reading
  • Possible rough running or exhaust smell if the system enters a default dosing strategy

Common causes, most likely first

  1. A short to battery voltage in the reductant pump control wire, often where the harness rubs against a frame rail or heat shield
  2. A failed reductant pump assembly with an open internal winding or failed control module
  3. Corroded or pushed-back terminals at the pump connector or at the engine control module connector
  4. A faulty reductant pump relay or fuse that is passing voltage when it should not
  5. Water or diesel exhaust fluid intrusion into the pump connector causing a conductive path
  6. A damaged engine control module driver circuit, though this is far less common than harness or pump faults

How to diagnose and fix it

  1. Read all stored and pending codes with a scan tool capable of accessing the reductant control module, and record freeze-frame data before clearing anything
  2. Inspect the reductant pump harness and connector for chafing, corrosion, fluid intrusion, and pushed terminals, repairing any damage found
  3. Disconnect the pump and key on to measure voltage on the control circuit; a reading near battery voltage with the pump unplugged points to a short to power
  4. Check the reductant pump relay and fuse, swapping a known-good relay and testing for voltage on the control circuit with the relay removed
  5. Measure resistance across the pump motor windings and compare to the manufacturer's specification to rule out an open or shorted pump
  6. Perform a commanded pump activation with the scan tool and watch live voltage and current data to confirm the circuit responds correctly
  7. If the harness and relay test good but the high voltage remains, replace the reductant pump assembly and recheck; only consider the engine control module after all other steps pass

What the high voltage reading really means

  • A high voltage code on a control circuit almost never means the pump is receiving too much power; it usually means the module sees voltage on a wire that should be pulled low, which points to an open circuit or a short to power rather than a failed pump.
  • Technicians often replace the reductant pump first and still have the code because the real fault is a chafed wire behind the fuel tank or a corroded connector pin that only acts up when the harness is wet.
  • A weak or failing battery can cause the module to set this code by misreading circuit voltage during cranking, so always verify battery health and charging voltage before condemning any component.
  • Diesel exhaust fluid crystallisation inside the pump connector can create a conductive bridge that mimics a short to power, so a visual inspection of the connector for white residue is a critical first step.
  • This code can be set by a reductant pump relay that sticks closed, feeding voltage to the control circuit even with the key off, which is why relay testing belongs in the diagnostic sequence before pump replacement.

Can I keep driving with P208D?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy loads and long trips because the engine control module may soon derate power or trigger a speed limitation. Do not ignore the warning light, as continued driving with an active reductant fault can lead to a no-start condition once the system's countdown expires.

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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