P248BReductant Heater A Sense Circuit High
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- 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.
- What you may notice
- Warning lamp
- Possible battery drain if the heater stays powered
- Likely causes
- PossibleHeater relay sticking closed
- PossibleSense lead shorted to battery voltage
- RareFaulty sense input in the control module
- 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.