P248A

Code

Generic P — Powertrain

Reductant Heater A Sense Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 18 EN: 39 RU: 22

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Malfunction Indicator Lamp (MIL) or DEF system warning on instrument cluster
Reduced or disabled reductant/DEF heating function (may show heater fault)
Possible reduction in aftertreatment performance or limp mode depending on vehicle
Inability to maintain reductant temperature in cold conditions

Read freeze frame and live data for reductant heater control and sense values
Inspect connectors and wiring at the reductant heater(s) and ECM for corrosion, damage, or looseness
Check relevant fuses and relays for continuity and proper operation
Measure battery voltage and charging system health
Perform a visual inspection of the reductant tank area and heater assembly for contamination or physical damage

Heater control output: typically 0 V when off, near battery voltage (approx. vehicle VBAT) when commanded on — verify with manufacturer spec
Heater sense/sensor signal: expected to be within manufacturer-specified range (often a low-voltage feedback 0–5 V or a resistance value); a persistent near 0 V or short to ground indicates a low condition
Heater element resistance: typically low ohms (varies by design) — consult service manual for exact resistance spec
Heater current draw when energized: can range from under 1 A to over 10 A depending on heater; compare to spec to detect open/short

Retrieve trouble code(s), freeze frame, and monitor live data for heater command and sense values. Note when code set (ambient/battery conditions).
Visually inspect wiring and connectors for damage, corrosion, moisture, or disconnection at the heater and ECM. Repair as needed.
Check fuses and relays in the heater power circuit; replace any blown fuses and test relay operation.
With ignition off, disconnect connector(s) and check continuity and for short to ground between the heater sense wire and chassis ground. Also check continuity to the ECM connector.
Measure heater element resistance at the heater terminals (with harness disconnected) and compare to service spec. Excessively high resistance or open indicates a failed heater element.
With backprobe or multimeter, verify that when the ECM commands the heater ON the control circuit is supplying battery voltage to the heater. Also monitor the sense signal for expected change when heater is energized.
Wiggle test wiring while monitoring live data to try to replicate intermittent faults. Repair any broken wires or poor crimps.
If wiring and heater check good, verify ECM outputs and grounds. If ECM output/sense circuit is faulty (no change when commanded), consider module diagnosis or replacement per manufacturer procedure.
After repairs, clear codes and perform a verification drive or heater cycle to ensure code does not return.

Damaged sense wire shorted to ground (low-voltage reading)
Disconnected or corroded connector at the heater harness
Internal failure of the reductant heater assembly (open/shorted element or sense sensor)
Blown fuse or bad heater relay preventing proper supply to the sense circuit
Poor ground at the heater or ECM causing erroneous low signal