What Does P20C5 Mean?
The PCM has detected an open circuit or lack of continuity in the control circuit for reductant heater D. This prevents proper operation of the DEF heating system.
Common Causes
35%
Open circuit in heater D control wiring
25%
Disconnected or corroded connector at heater D
20%
Failed reductant heater D element (open circuit)
15%
Broken or damaged ground circuit
5%
Failed reductant control module
Diagnostic Steps
1
Step 1: Inspect heater D connector for proper seating, bent pins, and corrosion damage
2
Step 2: Test continuity of control circuit from reductant module to heater D connector
3
Step 3: Measure resistance of heater D element between power and ground pins (should be 0.5-3 ohms typically)
4
Step 4: Check ground circuit continuity and verify clean, tight ground connections
5
Step 5: If all circuits test good, perform voltage drop test while commanding heater on to identify high resistance
Estimated Repair Cost
$200 - $850
Parts + labor, varies by vehicle and location
The PCM has detected an open circuit or lack of continuity in the control circuit for reductant heater D. This prevents proper operation of the DEF heating system.
The most common cause of P20C5 (Reductant Heater "D" Control Circuit/Open) is: Open circuit in heater D control wiring
Typical repair costs for P20C5 range from $200 to $850, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive but DEF system will not function properly. In freezing conditions, DEF may freeze and prevent vehicle operation until thawed.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20C5 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
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
