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Home / DTC / P2AD8 — Reductant Pump Motor Position Sensor Circuit Low

P2AD8 — Reductant Pump Motor Position Sensor Circuit Low

Detailed page for trouble code P2AD8.

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P2AD8

Generic P — Powertrain

Reductant Pump Motor Position Sensor Circuit Low

Brand: Generic
Type: P — Powertrain
Views: UK: 22 EN: 27 RU: 13
AI status
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Page language: EN

Causes

  • Short to ground on the sensor signal circuit
  • Open or damaged wiring / chafed harness
  • Corroded or loose connector at the sensor or module
  • Failed/weak position sensor (potentiometer or Hall element)
  • Low reference voltage or poor ground at sensor
  • Faulty control module (rare)

Symptoms

  • MIL / check engine or SCR warning lamp illuminated
  • Reduced or disabled reductant dosing; SCR system fault
  • One or more aftertreatment-related diagnostic messages
  • Possible limp-home or reduced engine performance if ECM limits operation
  • Difficulty starting SCR regeneration cycles or failed regen attempts

What to check

  • Read stored codes and freeze-frame data with a scan tool; note related DTCs
  • Visually inspect pump, sensor, wiring harness, and connectors for damage or corrosion
  • Backprobe sensor connector and measure signal voltage with key on / engine off and during operation
  • Verify sensor reference voltage (usually 5 V or manufacturer-specified) and ground quality
  • Perform wiggle test of wiring while monitoring live data to spot intermittent faults
  • Measure resistance of sensor (if specified) and compare to limits

Signal parameters

  • Typical position sensor signal: 0.5–4.5 V (varies with position) — low fault when below ~0.2–0.5 V (manufacturer dependent)
  • Reference voltage: nominally 5 V (verify with vehicle spec)
  • Ground:
  • If sensor is resistive/potentiometer type: typical total resistance often in the 1–10 kΩ range (refer to vehicle spec)
  • No significant fluctuation or dropout when pump motor rotates; signal should move smoothly through range

Diagnostic algorithm

  1. Connect a scan tool, confirm P2AD8 and any related codes, record freeze-frame/data stream and set-up for live data capture.
  2. Visually inspect wiring and connectors between reductant pump, position sensor and control module for damage, corrosion or pins pushed out.
  3. With ignition ON (engine OFF), backprobe connector: verify reference voltage present at sensor reference pin (typically ~5 V) and check that ground pin is good.
  4. Measure sensor signal voltage at rest and while actuating the pump (if safe). A steady very low voltage indicates a low circuit or short to ground.
  5. Check continuity from signal wire to ECM input and for short to ground: with ignition OFF, disconnect sensor and measure ohms from signal wire to chassis ground. Very low ohms indicates short to ground.
  6. If wiring and connectors check good, measure sensor resistance (if applicable) or bench-test sensor per manufacturer procedure. Replace sensor if out of specification.
  7. If sensor tests good on bench, inspect pump for mechanical binding that could hold sensor at extreme position; repair/replace pump assembly if needed.
  8. If sensor and wiring are good, check control module input circuit for shorts or damage. Substitute or repair module only after other causes eliminated.
  9. After repairs clear codes, perform functional test and road/operational test to confirm proper reductant dosing and that P2AD8 does not return.

Likely causes

  • Wiring short to ground or connector corrosion (most common)
  • Failed pump motor position sensor
  • Poor reference voltage or ground at sensor
  • Mechanical fault at pump causing abnormal sensor reading
  • Control module input circuit fault (least likely)

Fault status

⚠️ Status
P2AD8 set when reductant pump motor position sensor signal is below threshold (low voltage/resistance). Possible short to ground, connector/corrosion, sensor failure or poor reference/ground.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

P2AD9 P2ADA P2ADB P2263 P0620
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