What Does P20B1 Mean?
The ECM has detected an open circuit in the reductant heater coolant control valve. This valve regulates coolant flow through the DEF heating system, and an electrical circuit fault prevents proper operation.
Common Causes
30%
Open circuit in valve control wiring or connectors
30%
Failed coolant control valve solenoid (open coil)
20%
Blown fuse or failed relay in valve power supply circuit
15%
Corroded or disconnected connector at control valve
5%
ECM driver circuit failure
Diagnostic Steps
1
Step 1: Check relevant fuses and relays for reductant heater system; replace if blown and investigate cause
2
Step 2: Disconnect coolant control valve connector and measure resistance across valve terminals (typically 10-50 ohms)
3
Step 3: Check for battery voltage at valve connector power supply wire with key on
4
Step 4: Verify continuity of control and ground circuits from valve to ECM
5
Step 5: Replace valve if resistance is out of range or infinite; repair wiring if circuits fail continuity test
Estimated Repair Cost
$200 - $800
Parts + labor, varies by vehicle and location
The ECM has detected an open circuit in the reductant heater coolant control valve. This valve regulates coolant flow through the DEF heating system, and an electrical circuit fault prevents proper operation.
The most common cause of P20B1 (Reductant Heater Coolant Control Valve Circuit/Open) is: Open circuit in valve control wiring or connectors
Typical repair costs for P20B1 range from $200 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
DEF fluid may not heat properly in cold weather, leading to reduced emissions system effectiveness. May result in vehicle derate or power reduction after extended operation.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P20B1 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions Control System (SCR)
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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