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Home / DTC / P20F0 — SCR NOx Catalyst - Over Temperature Bank 2

P20F0 — SCR NOx Catalyst - Over Temperature Bank 2

Detailed page for trouble code P20F0.

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P20F0

Generic P — Powertrain

SCR NOx Catalyst - Over Temperature Bank 2

Brand: Generic
Type: P — Powertrain
Views: UK: 12 EN: 21 RU: 16
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Page language: EN

Causes

  • Actual over-temperature inside SCR (extreme exhaust heat or exothermic chemical reaction)
  • Faulty or shorted SCR temperature sensor (Bank 2)
  • Damaged/shorted wiring or poor connector at the SCR temperature sensor or SCR control module
  • Excessive or uncontrolled reductant (AdBlue/DEF) dosing or leaking injector(s)
  • Blocked/partially melted SCR catalyst or downstream exhaust restriction
  • Upstream high exhaust temperatures (extended DPF regen, turbocharger fault, severe engine misfire, unburned fuel reaching catalyst)

Symptoms

  • Malfunction Indicator Lamp (MIL) or system warning illuminated
  • Reduced engine performance or engine derate (limp mode) depending on manufacturer strategy
  • Increased DEF/AdBlue consumption or visible unusual exhaust odor/smoke in severe cases
  • Stored freeze frame data showing high exhaust/aftertreatment temperatures
  • Poor emissions performance / failed emissions test

What to check

  • Read and record freeze frame and live data (SCR temperature sensors, inlet/outlet temps, NOx sensor readings, DEF dosing rates)
  • Visually inspect temperature sensor, harness, and connector for corrosion, damage, or water ingress
  • Check sensor wiring continuity and for shorts to ground or battery with connector unplugged
  • Compare Bank 1 vs Bank 2 SCR temperature behavior (live data) for imbalance
  • Inspect DEF/urea dosing system (supply lines, injector/nozzle, heater, pump) for leaks or stuck injector
  • Scan for related codes (NOx sensor, DPF, EGR, fuel injection, ignition/misfire)

Signal parameters

  • Typical SCR operating temperatures: roughly 200–600°C during normal operation (varies by vehicle). Over-temperature event often above ~700°C–850°C (manufacturer-specific threshold).
  • Compare inlet (upstream) vs outlet (downstream) SCR temperatures — an unusually large positive delta (example: >100°C) may indicate exothermic reaction inside catalyst or local hotspot.
  • SCR temperature sensor types: thermistor or thermocouple. Expect a temperature-related voltage or resistance change; values are manufacturer-specific so compare to factory spec.
  • DEF/urea dosing: check commanded dosing rate vs actual (excessive commanded dosing or continuous pulse may indicate dosing faults).
  • NOx sensor readings (upstream/downstream) may show anomalous values if SCR is not functioning or damaged.

Diagnostic algorithm

  1. Retrieve all relevant trouble codes and freeze-frame data. Note engine load, vehicle speed, and temperatures at time of fault.
  2. Inspect the SCR temperature sensor connector and wiring for damage, corrosion, or disconnection. Repair any physical faults.
  3. Monitor live SCR temperature sensors (Bank 1 and Bank 2). Look for intermittent spikes, implausible values, or fixed outputs that indicate sensor failure.
  4. If sensor wiring appears intact, bench-test or measure sensor resistance/voltage against manufacturer data (or substitute test method if spec unavailable). Replace sensor if out of tolerance.
  5. Use an infrared pyrometer or thermocouples to independently verify exhaust and catalyst surface temperatures while reproducing the condition (take safety precautions).
  6. Inspect DEF/urea dosing system: check supply, heater, injector operation, and look for leaks or crystallized deposits near injector/nozzle that could cause localized overreaction.
  7. Check upstream systems that can raise exhaust temp: DPF regeneration history, EGR operation, turbocharger condition, and engine misfires/incorrect fueling.
  8. If temperatures are confirmed high and sensors/wiring/dosing system are OK, inspect SCR catalyst for internal damage. Significant damage usually requires catalytic converter/SCR replacement.
  9. If wiring and sensor replacement do not clear the condition, consider SCR control module or ECM software/firmware issues and consult manufacturer service information.
  10. After repairs, clear codes and perform road test and thermal verification to ensure temperatures remain within acceptable range and no reoccurrence.

Likely causes

  • Temperature sensor failure or intermittent wiring/connector fault (most common)
  • Excessive reductant dosing or stuck/shorted dosing injector causing local hotspots
  • High upstream exhaust temperature event (DPF regeneration/misfire) transferring heat to SCR
  • Partial catalyst damage or internal blockage causing localized heating
  • SCR control module fault or incorrect calibration

Fault status

⚠️ Status
SCR NOx Catalyst over-temperature detected on Bank 2. Possible causes include sensor or wiring failure, excessive reductant reaction, upstream high exhaust temperatures, or catalyst damage. Inspect sensor, wiring, dosing system and exhaust components.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 2-6 hours

Similar codes

P20E0 P0420 P2463 P2499 P20D0
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