What Does P20B6 Mean?
The PCM has detected that the reductant metering unit heater is not performing within expected parameters. The heater may be drawing incorrect current, heating too slowly, or not reaching target temperature.
Common Causes
40%
Partially failed or degraded reductant metering unit heater element
25%
Low voltage supply to heater circuit due to poor connections or battery issues
20%
High resistance in heater control circuit wiring
10%
Faulty temperature sensor in reductant metering unit
5%
PCM or DEF control module software issue or hardware fault
Diagnostic Steps
1
Step 1: Monitor heater current draw and voltage during operation using scan tool live data and multimeter
2
Step 2: Check battery voltage and charging system output (should be 13.5-14.5V running)
3
Step 3: Measure heater element resistance and compare to specifications across temperature range
4
Step 4: Inspect all power and ground connections for high resistance using voltage drop testing
5
Step 5: Monitor DEF temperature sensor readings and compare to ambient temperature
Estimated Repair Cost
$200 - $900
Parts + labor, varies by vehicle and location
The PCM has detected that the reductant metering unit heater is not performing within expected parameters. The heater may be drawing incorrect current, heating too slowly, or not reaching target temperature.
The most common cause of P20B6 (Reductant Metering Unit Heater Control Circuit Performance) is: Partially failed or degraded reductant metering unit heater element
Typical repair costs for P20B6 range from $200 to $900, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive but DEF system effectiveness may be reduced in cold conditions. Potential for power derate if left unrepaired in cold climates.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20B6 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions Control System - SCR/DEF
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
