What Does P20C6 Mean?
The PCM has detected that reductant heater D is not performing as expected, either heating too slowly, too quickly, or drawing incorrect current. This indicates a degraded or failing heater element.
Common Causes
40%
Degraded reductant heater D element with altered resistance
25%
High resistance in power or ground circuits
15%
Low system voltage affecting heater performance
12%
Contaminated DEF affecting heat transfer
8%
Faulty reductant control module current sensing
Diagnostic Steps
1
Step 1: Monitor heater D current draw with scan tool or ammeter during operation and compare to specifications
2
Step 2: Measure heater D element resistance and compare to factory specifications (resistance changes with temperature)
3
Step 3: Perform voltage drop test on both power and ground circuits while heater is operating (should be less than 0.5V total)
4
Step 4: Test battery and charging system to ensure adequate voltage supply (should maintain above 13V)
5
Step 5: If circuits and voltage are good but current is out of range, replace heater D element
Estimated Repair Cost
$250 - $900
Parts + labor, varies by vehicle and location
The PCM has detected that reductant heater D is not performing as expected, either heating too slowly, too quickly, or drawing incorrect current. This indicates a degraded or failing heater element.
The most common cause of P20C6 (Reductant Heater "D" Control Circuit Performance) is: Degraded reductant heater D element with altered resistance
Typical repair costs for P20C6 range from $250 to $900, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive but may experience reduced performance. Incomplete DEF heating can lead to system freezing in cold weather and potential no-start conditions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20C6 to identify the root cause.
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Quick Info
Category
Powertrain
System
Diesel Emissions System (SCR/DEF)
Difficulty
Type
Generic (SAE)
Recommended Tools
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