Code
U05A5
Generic
U — Network/User
Invalid Data Received From NH3 Sensor
AI status
Completed
Completed
100%
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
- Record U05A5 and any other codes; save freeze-frame and live-data snapshots.
- Clear codes and reproduce conditions to see if code returns. Note intermittent vs permanent.
- Visually inspect sensor, connector, and harness for damage, contamination, or loose pins.
- With ignition on, backprobe sensor power and ground. Verify correct supply voltage and good ground continuity to chassis.
- Check heater circuit (resistance and applied voltage) per manufacturer specs; a failed heater can produce invalid readings at low temperature.
- Monitor live NH3 sensor output and temperature while varying conditions (engine running, aftertreatment warm-up). Compare values to expected ranges.
- Use a scope or CAN/LIN diagnostic tool to check signal waveform and bus messages for corruption, bus errors, or missing frames.
- If wiring or connector faults are found, repair or replace harness and re-test. Use pin cleaning or replacement as needed.
- If wiring checks good and communication is stable but sensor values are implausible or out of range, replace the NH3 sensor and retest.
- If code persists after sensor replacement, check ECU/aftertreatment module software level and consider reflash or module replacement per manufacturer guidance.
- 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
Repair manuals
Brands with available manuals
8,080
The library contains 8,080 repair and diagnostic manuals. Choose a brand to open the full manual tree by year, model and trim.
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email