U05A1

Code

Generic U — Network/User

NOx Sensor A Received Invalid Data From ECM/PCM

Brand: Generic

Type: U — Network/User

Views: UK: 29 EN: 39 RU: 34

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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)

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

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

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

Verify and record all related DTCs from all modules; identify whether other modules report communication faults.
Attempt to communicate with both the NOx module and ECM/PCM using a scan tool. Note failures, timeouts, or intermittent responses.
Visually inspect connectors and harness between NOx module and ECM/PCM. Repair any corrosion, pin damage or water intrusion.
Check power and ground to the NOx module and ECM/PCM. Repair any low-voltage or poor-ground symptoms before further testing.
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.
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.
Perform wiggle testing of harnesses/connectors while monitoring live communication to locate intermittent faults.
If wiring and bus appear healthy, verify software/calibration levels on ECM and NOx module. Compare to OEM levels and apply updates if required.
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.
After repair, clear codes, reinitialize modules if required, and run a road/test cycle or communication stress test to confirm issue resolution.

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