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Home / DTC / U05A5 — Invalid Data Received From NH3 Sensor

U05A5 — Invalid Data Received From NH3 Sensor

Detailed page for trouble code U05A5.

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U05A5

Generic U — Network/User

Invalid Data Received From NH3 Sensor

Brand: Generic
Type: U — Network/User
Views: UK: 11 EN: 12 RU: 10
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Page language: EN

Causes

  • NH3 sensor internal failure or contamination
  • Open, short or high-resistance wiring between sensor and control module
  • Corroded, loose, or damaged connector/pins
  • Loss of sensor power, ground, or heater circuit fault
  • CAN/LIN communication errors or bus interruptions
  • Faulty or misconfigured ECM/aftertreatment control module software

Symptoms

  • Malfunction Indicator Lamp (MIL) or warning for aftertreatment system
  • Reduced aftertreatment performance, increased NOx emissions
  • Regeneration or SCR derate, possible limp mode depending on vehicle
  • Diagnostic trouble codes stored (U05A5 plus related network or sensor codes)
  • Possible poor fuel economy or driveability degradation in severe cases

What to check

  • Read all stored, pending and freeze-frame codes with a capable scan tool
  • Inspect NH3 sensor connector and wiring for corrosion, damage, looseness
  • Check vehicle battery voltage and main grounds for good connections
  • Verify DEF/AdBlue level and quality (contamination can damage sensors)
  • Monitor live data for NH3 sensor values, sensor temperature, and heater status
  • Check CAN/LIN bus health: bus voltages, resistors, and presence of other node errors

Signal parameters

  • NH3 concentration (ppm) or mapped value reported by sensor
  • Sensor output voltage or current range (manufacturer-specific, e.g., 0–5 V or 4–20 mA)
  • Sensor temperature or internal heater status (°C and heater duty / voltage)
  • CAN/LIN message ID and payload containing NH3 sensor data
  • Message update rate (Hz) and timeout thresholds
  • Status bits/flags indicating sensor health, range, and heating state

Diagnostic algorithm

  1. Record U05A5 and any other codes; save freeze-frame and live-data snapshots.
  2. Clear codes and reproduce conditions to see if code returns. Note intermittent vs permanent.
  3. Visually inspect sensor, connector, and harness for damage, contamination, or loose pins.
  4. With ignition on, backprobe sensor power and ground. Verify correct supply voltage and good ground continuity to chassis.
  5. Check heater circuit (resistance and applied voltage) per manufacturer specs; a failed heater can produce invalid readings at low temperature.
  6. Monitor live NH3 sensor output and temperature while varying conditions (engine running, aftertreatment warm-up). Compare values to expected ranges.
  7. Use a scope or CAN/LIN diagnostic tool to check signal waveform and bus messages for corruption, bus errors, or missing frames.
  8. If wiring or connector faults are found, repair or replace harness and re-test. Use pin cleaning or replacement as needed.
  9. If wiring checks good and communication is stable but sensor values are implausible or out of range, replace the NH3 sensor and retest.
  10. If code persists after sensor replacement, check ECU/aftertreatment module software level and consider reflash or module replacement per manufacturer guidance.
  11. After repair, erase codes and complete a road/drive cycle or specified verification procedure to confirm repair.

Likely causes

  • Damaged connector or corroded pin causing intermittent or invalid messages
  • Open/short in signal or CAN/LIN wiring
  • Sensor heater not functioning leading to invalid readings at low temp
  • Sensor contamination or age-related drift producing out-of-range values
  • Module communication fault (bus off, incorrect node addressing) or software bug

Fault status

⚠️ Status
Invalid data received from NH3 sensor — communication or signal out-of-range/corrupted.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0415 U0401 U0100 U0121 U0073
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