Powertrain, generic (extended)

P248A Reductant Heater A Sense Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P248A concerns the sense line with which the control unit measures the supply voltage reaching DEF heater A, and reports that voltage as too low. GM uses it on its diesels with an SCR power module for the tank heater: the 2016 to 2018 tables subtract the heater supply voltage from system voltage and fail a gap of more than 3 V while heating is commanded, after 10 of 12 checks at 500 ms; cranking is excluded and a lost connection to the reductant module (U010E) blocks the test. The tables leave the lamp column blank. Ford's 2023 diesels also assign heater A to the tank. A voltage drop of this size usually comes from a corroded plug, a weak relay contact or a damaged supply lead.

Likely causes

Corroded heater supply connector at the tank
Worn heater relay contact causing voltage drop
Weak battery or charging fault during heating

Symptoms

  • Warning lamp or DEF system message
  • Frozen DEF not thawed in winter, dosing delayed

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

P248BP248CP248DP20B9P20BB

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