Powertrain, generic (extended)

P248D Reductant Heater B Sense Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P248D means the heater B sense input reads too high, typically the heated line. Possible pictures are a sense wire shorted to battery positive, a supply that remains on after the heater has been switched off, or a faulty input stage. Public maker documentation for P248D does not exist. GM tests the line heater sense circuit only for undervoltage (P248C); Ford's 2023 diesels cover heater circuit 2, the pressure line heater, with P20C0 (switched off yet more than 5 V at the output) and the current codes P221C/P221D. CARB requires the reductant heating to be monitored. A line heater that never switches off wastes battery energy and can overheat the hose, so the relay is the first item to check.

Likely causes

Line heater relay sticking closed
Sense wire shorted to battery positive
Defective input stage in the module

Symptoms

  • Warning lamp
  • Battery discharging while parked

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

P248AP248BP248CP20C0P221C

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