Powertrain, generic (extended)

P248C Reductant Heater B Sense Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P248C reports too little voltage on the sense circuit of DEF heater B. In GM's diesel tables from 2016 to 2018 heater B is the line heater, i.e. the heated hose from the pump to the dosing valve. The test mirrors P248A: if system voltage exceeds the measured line heater supply by more than 3 V while heating is requested, 10 failures in 12 checks at 500 ms set the code, with cranking excluded and U010E as a blocking condition; no lamp type is listed. Ford's 2023 diesels likewise give the pressure line heater the letter B. A frozen hose that does not thaw causes dosing faults in winter, so a voltage drop at the line heater plug or in its fuse and relay path should be found early.

Likely causes

Corroded plug at the heated DEF line
Voltage drop across fuse or relay of the line heater
Damaged supply lead along the frame

Symptoms

  • DEF warning or engine lamp
  • Dosing faults at low temperatures

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–700
Time0.5–3 h

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

Parts involved

reductant heater b

Related codes

P248AP248BP248DP20BDP20BE

References: gsi.ext.gm.com, gsi.ext.gm.com, fordservicecontent.com.