What Does P20C0 Mean?
The PCM has detected abnormally high voltage in the control circuit for reductant heater B. This indicates a short to voltage condition that prevents proper heater control and may damage components.
Common Causes
35%
Damaged wiring with short to battery voltage or power circuit
30%
Internal short to voltage in reductant heater B
20%
Failed heater control module with shorted driver circuit
10%
Connector damage causing cross-circuit short to power
5%
Incorrect repair or wiring modification causing miswire
Diagnostic Steps
1
Step 1: Disconnect heater B connector and measure voltage on control circuit wire (should be 0V with key on if shorted externally)
2
Step 2: Check for short to voltage in wiring harness using multimeter with heater disconnected
3
Step 3: Measure resistance of heater element and check for internal shorts to power terminal
4
Step 4: Inspect wiring harness for damage, especially where it runs near power distribution or battery cables
5
Step 5: Test heater control module output with scan tool commanding heater off (should show 0V at module output)
Estimated Repair Cost
$200 - $850
Parts + labor, varies by vehicle and location
The PCM has detected abnormally high voltage in the control circuit for reductant heater B. This indicates a short to voltage condition that prevents proper heater control and may damage components.
The most common cause of P20C0 (Reductant Heater "B" Control Circuit High) is: Damaged wiring with short to battery voltage or power circuit
Typical repair costs for P20C0 range from $200 to $850, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Generally safe to drive short distances. Short to voltage condition may cause component damage if left unrepaired and can lead to DEF system failure in cold weather conditions.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20C0 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions - Selective Catalytic Reduction (SCR)
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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