Powertrain, generic (extended)

P20B1 Reductant Heater Coolant Control Valve Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Many heavy-duty SCR systems thaw the DEF tank and supply module with engine coolant, and an electrically switched valve decides when that warm coolant may circulate; Bosch offers its larger supply modules with either electric or cooling-water heating. P20B1 is set when the control unit finds the drive circuit of this valve open or otherwise defective. No manufacturer documents P20B1 publicly. Hino, which fits such a coolant cutoff valve, explains in TT-16-014 that once its dosing control unit detects an open load it stops powering the valve until a UREA SCR memory reset, so circuit tests only work while the valve stays connected. Without a working valve, DEF stays frozen longer in winter.

Likely causes

Valve connector unplugged, loose or corroded
Open solenoid coil in the coolant valve
Broken wire between control unit and valve

Symptoms

  • Malfunction indicator and SCR warning on
  • DEF thaws slowly or not at all in cold weather
  • Valve does not click during an actuator test

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–600
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant coolant valve

Related codes

P20B2P20B3P20B4P202AP205B

References: law.cornell.edu, static.nhtsa.gov, boschaftermarket.com, en.wikipedia.org.