P248AReductant Heater A Sense Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- 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.
- What you may notice
- Warning lamp or DEF system message
- Frozen DEF not thawed in winter, dosing delayed
- Likely causes
- LikelyCorroded heater supply connector at the tank
- PossibleWorn heater relay contact causing voltage drop
- RareWeak battery or charging fault during heating
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.