P248CReductant Heater B Sense Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P248C reports too little voltage on the sense circuit of DEF heater B. In GM's diesel tables from 2016 to 2018 heater B is the line heater, i.e. the heated hose from the pump to the dosing valve. The test mirrors P248A: if system voltage exceeds the measured line heater supply by more than 3 V while heating is requested, 10 failures in 12 checks at 500 ms set the code, with cranking excluded and U010E as a blocking condition; no lamp type is listed. Ford's 2023 diesels likewise give the pressure line heater the letter B. A frozen hose that does not thaw causes dosing faults in winter, so a voltage drop at the line heater plug or in its fuse and relay path should be found early.
- What you may notice
- DEF warning or engine lamp
- Dosing faults at low temperatures
- Likely causes
- LikelyCorroded plug at the heated DEF line
- PossibleVoltage drop across fuse or relay of the line heater
- RareDamaged supply lead along the frame
- 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 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.