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Home / DTC / P248C — Reductant Heater B Sense Circuit Low

P248C — Reductant Heater B Sense Circuit Low

Detailed page for trouble code P248C.

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Code

P248C

Generic P — Powertrain

Reductant Heater B Sense Circuit Low

Brand: Generic
Type: P — Powertrain
Views: UK: 10 EN: 23 RU: 15
AI status
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Page language: EN

Causes

  • Open or shorted wiring in Heater B sense circuit (short to ground)
  • Corroded, loose, or damaged connector at heater or control module
  • Failed/heavily degraded reductant heater B element or internal sense resistor
  • Blown fuse or defective relay supplying the heater circuit
  • Low battery or poor power/ground affecting sensor readings
  • Faulty PCM/ECM or internal sense circuit fault

Symptoms

  • MIL (Check Engine lamp) illuminated
  • Service message related to DEF/reductant heater or NOx system
  • Reduced or disabled reductant heating (poor cold-weather performance)
  • Possible engine derate or reduced emissions control performance
  • Diagnostic trouble codes related to reductant/heater circuits present

What to check

  • Read and record DTC(s), freeze frame and live data for reductant heater B sense line
  • Perform a visual inspection of DEF tank, heater assembly, harness and connectors for corrosion, damage or contamination
  • Check fuses and relays for the reductant/heater circuit
  • With ignition ON (engine off) monitor sense circuit voltage at the PCM and at the heater connector using a DVOM or scope
  • Measure heater element resistance at the connector with power removed (compare to spec)
  • Perform continuity checks from heater connector to PCM pin and to ground; check for shorts to ground or battery

Signal parameters

  • Normal sense voltage (typical): ~0.5–4.5 V (vehicle-specific)
  • Trip/Low condition: sense voltage below expected threshold (often
  • Heater element resistance (typical): low ohms to tens of ohms — vehicle-specific
  • Heater current when active: may be 1–10 A (vehicle-specific)

Diagnostic algorithm

  1. Obtain freeze frame and note conditions when DTC set. Clear codes and attempt to re-create.
  2. Visually inspect harness, connectors and DEF heater assembly for damage, corrosion, or fluid intrusion. Repair or clean as required.
  3. Check related fuses and relays for continuity and proper operation; replace if faulty.
  4. Disconnect battery or disable circuit power before performing resistance tests. With power removed, measure resistance of Heater B element between its terminals and compare to specification.
  5. With harness connected and ignition ON (engine OFF), backprobe the heater sense terminal at the PCM and at the heater connector. Verify reference voltage/sense voltage is within expected range.
  6. If sense voltage is low, test for short to ground on the sense wire (continuity to ground). If short present, isolate by disconnecting sections of harness until short clears.
  7. If wiring and connectors are good but heater resistance or sense still out of spec, replace the reductant heater assembly (or heater module) and recheck.
  8. If replacement heater does not correct the condition, check PCM power/grounds and consider upgrading/reprogramming or replacing PCM as a last step.
  9. After repairs, clear codes and run the vehicle through required readiness/drive cycles and verify heater operation and that the code does not return.

Likely causes

  • Short to ground in the sense wire
  • Corroded connector pin at heater or module
  • Failed heater element or internal sensing component
  • Blown fuse or bad relay feeding the heater
  • Poor ground or supply to the heater circuit

Fault status

⚠️ Status
Reductant Heater B Sense Circuit Low — heater B sense voltage below expected range
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P2487 P2488 P248B P20EE P20F4
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