Powertrain, generic (extended)

P20BD Reductant Heater B Control Circuit/Open

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modePossible

Heater B's control circuit is open. In GM's tables heater 2 is the DEF line heater; the 2025 version detects the open state with the output off and sets a Type A code after two seconds, while the 2018 version relies on an open status reported by the DEF control module with battery voltage above 11 V. Deutz assigns B to the pressure line heater, the hose from pump to dosing valve. Hino numbers differently: its 2018 bulletin calls P20BD heater 1 of the heated DEF line on J05 cab-overs and asks for a resistance check at the 6-pin connector before the line assembly is replaced. On the Touareg CNRB, VW stores the code when the power stage's diagnostic signal drops below 4.70 V. A frozen pressure line delays or blocks dosing in cold weather. Short circuits of the same element are P20BF and P20C0.

Likely causes

Heating wire in the pressure line broken (line assembly replacement)

Corroded or unplugged line heater connector

Harness to the line heater damaged along the frame rail

Symptoms

Warning lamp, especially after cold nights
DEF pressure builds slowly or not at all in frost
Inducement countdown with eventual speed limit

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€80–700

Time0.5–3 h

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

Parts involved

reductant line heater b

References: static.nhtsa.gov, gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.