P248B code meaning
Reductant Heater A Sense Circuit High
Powertrain system Generic code P24xx codes Check engine light
What P248B means
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.
P248B at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P248B
- Warning lamp
- Possible battery drain if the heater stays powered
Common causes of P248B
- PossibleHeater relay sticking closed
- PossibleSense lead shorted to battery voltage
- Less likelyFaulty sense input in the control module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant heater a
What each part of P248B means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 8B | The exact fault in that area. |
What to do next
- Note P248B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P248B
What does P248B mean?
P248B means "Reductant Heater A Sense Circuit High". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P248B?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P248B fail an emissions test?
Yes, it can. P248B is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P248B to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P248B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.