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DTC codes / P20xx · Fuel and air metering and auxiliary emission controls / P20BE

P20BEReductant Heater B Control Circuit Performance

P20BE indicates that the engine control module has detected a performance fault in the control circuit for reductant heater B, which is the heating element used to keep diesel exhaust fluid (DEF) from freezing in cold weather. The computer monitors the heater circuit for expected current draw and response, and when the circuit does not behave as commanded, it sets this code and illuminates the check engine light.

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 indicating a DEF system fault or that the vehicle will be limited in miles before service.
  • In cold weather, the vehicle may enter a reduced power or limp mode if the DEF heater cannot thaw the fluid.
  • Longer than normal DEF thaw times after a cold start, which may delay the start of selective catalytic reduction (SCR) dosing.
  • In some cases, a no-start condition if the DEF system is completely frozen and the heater circuit is inoperative.
  • Possible stored freeze frame data showing low ambient temperatures when the fault occurred.

Common causes, most likely first

  1. A failed reductant heater element B, such as an open or shorted heating coil.
  2. Damaged or corroded wiring or connector pins in the heater control circuit, often due to road debris or moisture intrusion.
  3. A faulty reductant heater control module or relay that does not supply the commanded current.
  4. A blown fuse or fusible link that powers the heater circuit.
  5. A software issue in the engine control module or reductant control module that misinterprets heater performance.
  6. A defective temperature sensor for the reductant tank that provides incorrect feedback, causing the control module to command the heater incorrectly.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in the reductant and engine control systems.
  2. Inspect the reductant heater fuse and relay, and replace any that are blown or faulty.
  3. Visually inspect the heater wiring and connectors for damage, corrosion, or loose pins, and repair as needed.
  4. Measure the resistance of the reductant heater element with a multimeter and compare it to the manufacturer's specification.
  5. Check for power and ground signals at the heater connector while commanding the heater on with a scan tool.
  6. If the circuit and heater test good, suspect the reductant control module or engine control module and follow the manufacturer's diagnostic flow for module testing.
  7. After repairs, clear the codes and perform a relearn or drive cycle to confirm the heater circuit operates correctly.

Reductant heater faults that fool technicians

  • A common oversight is replacing the heater element when the actual problem is a corroded connector pin that creates high resistance only under load, which a simple resistance check may not reveal.
  • The code can be set by a heater that draws too much current due to a shorted coil, which may blow the fuse intermittently and leave no obvious sign until the circuit is load-tested.
  • Some vehicles use a pulse-width-modulated signal to control the heater, and a standard test light may not provide a valid load, leading to a false conclusion that the control module is faulty.
  • A reductant temperature sensor that reads incorrectly can cause the control module to command the heater when it is not needed, eventually setting a performance code for the heater circuit.
  • After a heater circuit repair, some vehicles require a scan-tool routine to reset the learned heater parameters, and skipping this step can cause the code to return immediately.

Can I keep driving with P20BE?

You can usually continue driving with this code, but the vehicle may enter a reduced power or no-start condition in freezing temperatures if the DEF heater is inoperative. Avoid long trips in cold weather until the fault is repaired, and do not ignore a driver message that counts down to a speed limitation.

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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