Powertrain, generic (extended)

P248B Reductant Heater A Sense Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P248B is the upper counterpart to P248A: the sense signal for the supply of DEF heater A reads higher than permitted, for example when the line shorts to battery voltage, when the supply stays live although the heater is switched off, or when the sense input itself fails. No manufacturer documents P248B in public material. GM's diesels only check the low side of this sense line (P248A, more than 3 V below system voltage); Ford's 2023 diesels flag a heater supply below 5 V and check the switched-off state of heater circuit 1, the tank heater, under P20BC. CARB requires reductant heaters and their circuits to be monitored. In practice, check whether the heater relay releases and whether the sense lead is intact.

Likely causes

Heater relay sticking closed
Sense lead shorted to battery voltage
Faulty sense input in the control module

Symptoms

  • Warning lamp
  • Possible battery drain if the heater stays powered

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–900
Time0.5–3 h

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

Parts involved

reductant heater a

Related codes

P248AP248CP248DP20BCP20B9

References: law.cornell.edu, gsi.ext.gm.com, fordservicecontent.com.