What are the common causes of P20B5?

An open in the reductant metering unit heater control circuit. A failed reductant metering unit heater. A backed out pin at the metering unit heater connector. Chafed wiring along the heater harness.

Command the reductant metering unit heater with a scan tool. Test the heater control circuit for an open. Check the heater connector pins. Test the heater element resistance against spec. Replace the reductant metering unit heater if faulty. Clear the code and retest.

P20B5

Reductant Metering Unit Heater Control Circuit/Open

System: Fuel and air metering (P code)
Lamp: Check Engine Light
Category: Powertrain - Fuel/Air Metering

What it means

P20B5 means Reductant Metering Unit Heater Control Circuit/Open.

Check these first

An open in the reductant metering unit heater control circuit
A failed reductant metering unit heater
A backed out pin at the metering unit heater connector
Chafed wiring along the heater harness

What to do next

Command the reductant metering unit heater with a scan tool
Test the heater control circuit for an open
Check the heater connector pins
Test the heater element resistance against spec
Replace the reductant metering unit heater if faulty
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.