P20B1 — Reductant-heater coolant valve control circuit — circuit fault/open

P20B1 concerns reductant-heater coolant valve control circuit. The fault label concerns the electrical circuit and includes an open-circuit condition; it does not identify the failed part. The component controls the coolant route used by the reductant heating system. The label does not establish a low coolant temperature.

Affected system: Reductant dosing and SCR aftertreatment

Symptoms

• Warning light may illuminate
• Related system function may be impaired
• Vehicle-specific symptoms vary

Possible causes

• Mechanical timing or operating issue, sensor or actuator fault, connector or wiring damage
• Related wiring, connector, power or ground fault
• Vehicle-specific mechanical or control issue

What to check

• Record stored and pending codes and freeze-frame data
• Record freeze-frame conditions; compare relevant live data and inspect mechanical operation, wiring and related fault codes before replacing parts.
• Confirm measured values against the vehicle service information
• Retest under the conditions that set the code
• Record freeze-frame conditions; compare relevant live data and inspect mechanical operation, wiring and related fault codes before replacing parts.
• Repair the verified cause and confirm the code does not return

Also written as: P20B1-00, P20B100 (some scan tools add the fault-type byte, e.g. -00).