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Home / DTC / U05A1 — NOx Sensor A Received Invalid Data From ECM/PCM

U05A1 — NOx Sensor A Received Invalid Data From ECM/PCM

Detailed page for trouble code U05A1.

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U05A1

Generic U — Network/User

NOx Sensor A Received Invalid Data From ECM/PCM

Brand: Generic
Type: U — Network/User
Views: UK: 14 EN: 23 RU: 18
AI status
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Page language: EN

Causes

  • Open, short or intermittent wiring in communications harness (CAN/LIN) between NOx module and ECM/PCM
  • Corroded, loose or damaged connectors at the NOx sensor module, ECM/PCM or intermediate junctions
  • Failed or misconfigured ECM/PCM or NOx control module software (firmware mismatch or bug)
  • Bus termination or wiring impedance problem (missing/failed 120 Ω termination, short to battery or ground)
  • Electrical supply or ground faults to the NOx module or ECM/PCM causing corrupt transmissions
  • Interference or noise on the data bus (aftermarket devices, damaged shielding)

Symptoms

  • Malfunction Indicator Lamp (MIL)/Check Engine Light illuminated
  • Aftertreatment warnings (DPF/DEF/Nox system warnings) or reduced performance of emissions systems
  • Regeneration failures, altered DEF dosing or limp-inhibit of regen events
  • Reduced engine performance or limp-home mode in some vehicles if ECM protects system
  • Stored communication and NOx-related diagnostic trouble codes
  • Possible inability for scan tool to read NOx module data or live NOx values

What to check

  • Read all stored and pending codes from ECM, NOx module and other network modules; capture freeze frame and occurrence counts
  • Verify ability to communicate with ECM/PCM and NOx module via scan tool; note any communication errors
  • Inspect connectors and wiring for the NOx module and ECM/PCM for corrosion, bent pins, water ingress, or damage
  • Check module supply voltage and ground(s) with key on and engine running; compare to specification
  • Perform wiggle test on harness and connectors while monitoring communication and live data
  • Measure CAN/LIN bus voltages with a multimeter and compare to expected idle values; check for short to battery/ground

Signal parameters

  • Typical CAN idle voltages: CAN_H ≈ 2.5–2.7 V, CAN_L ≈ 2.3–2.5 V (each about 2.5 V when recessive)
  • Dominant CAN state: CAN_H ≈ 3.5–3.8 V and CAN_L ≈ 1.0–1.5 V (differential ≈ 2 V)
  • Termination: two 120 Ω resistors in parallel across CAN_H and CAN_L (~60 Ω measured end-to-end)
  • Common CAN bus data rates: 250 kbps or 500 kbps (confirm vehicle-specific rate)
  • LIN/SWC (if used) typical idle ~12 V or ~5 V depending on design; check OEM specs for NOx sensor interface

Diagnostic algorithm

  1. Verify and record all related DTCs from all modules; identify whether other modules report communication faults.
  2. Attempt to communicate with both the NOx module and ECM/PCM using a scan tool. Note failures, timeouts, or intermittent responses.
  3. Visually inspect connectors and harness between NOx module and ECM/PCM. Repair any corrosion, pin damage or water intrusion.
  4. Check power and ground to the NOx module and ECM/PCM. Repair any low-voltage or poor-ground symptoms before further testing.
  5. Measure CAN_H and CAN_L with key on using a multimeter; if voltages are out of range, isolate short/open by disconnecting modules one at a time and rechecking bus voltage.
  6. Use an oscilloscope to check CAN differential waveform while commanding data or during engine/run conditions. Look for noise, missing edges, stuck dominant/recessive bits or arbitration faults.
  7. Perform wiggle testing of harnesses/connectors while monitoring live communication to locate intermittent faults.
  8. If wiring and bus appear healthy, verify software/calibration levels on ECM and NOx module. Compare to OEM levels and apply updates if required.
  9. If a single module is confirmed to be sending corrupt messages and wiring, power/grounds are good, consider replacing the faulty module (NOx control module or ECM) as directed by manufacturer procedures.
  10. After repair, clear codes, reinitialize modules if required, and run a road/test cycle or communication stress test to confirm issue resolution.

Likely causes

  • Damaged or corroded connector at NOx module or ECM wiring harness
  • Intermittent CAN/LIN wiring break caused by chafe or repair
  • Failed NOx control module or ECM after software update
  • Poor ground or low supply voltage to the NOx module causing data errors
  • Missing/failed termination resistor or short on CAN high/low causing invalid messages

Fault status

⚠️ Status
NOx Sensor A received invalid or corrupted data from ECM/PCM — communication/data integrity fault on vehicle network (CAN/LIN).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U0100 U0155 U0415 U0422 U0073
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