U05A2

Code

Generic U — Network/User

NOx Sensor B Received Invalid Data From ECM/PCM

Brand: Generic

Type: U — Network/User

Views: UK: 28 EN: 35 RU: 32

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Faulty NOx sensor B (internal failure or contamination)
Damaged/corroded connector or wiring between NOx sensor B and ECM/PCM
Poor power or ground to the NOx sensor (heater or sensor electronics)
CAN/LIN or vehicle communication bus faults or excessive bus errors
ECM/PCM software bug, corrupted calibration, or improper reprogramming
Interference from aftermarket modules or adapters affecting data

Symptoms

Malfunction Indicator Lamp (MIL) or warning lamp illuminated
Loss of NOx B data visible on a scan tool or implausible NOx readings
Reduced emissions control performance, DPF regen issues, or forced regen disabled
Possible engine derate or reduced performance in some vehicles
Related communication or multiple U-codes stored in other modules

What to check

Read and record all stored U- and P-codes and freeze frame data with a capable scan tool
Check live data: NOx B values, heater status/current/power, compare NOx A vs NOx B
Inspect NOx sensor B connector and wiring for corrosion, pin damage, or disconnection
Verify battery voltage and grounds while running and during fault occurrence
Scan the vehicle network for bus errors, lost messages, or other module communication faults
Check for recent PCM/ECM reflashes, module replacements, or installed aftermarket devices

Signal parameters

NOx sensor output: typically an electrical signal or CAN message representing NOx concentration (typical analog 0–5.0 V range for some sensors; many systems use CAN messages carrying ppm values)
NOx concentration range: typically 0–2000 ppm reported (varies by system)
Heater resistance: typically a low-ohm value (order of 1–20 Ω) — consult vehicle-specific spec
Heater current: varies by system, monitored during warm-up (expected current draw in service manual)
CAN bus idle voltages: approx. 2.5 V per bus line (differential signals; overall bus termination ~60 Ω)

Diagnostic algorithm

Retrieve all codes and freeze frame data; note occurrence conditions and related codes.
Check for TSBs and any available ECM/PCM software updates or calibration changes for NOx sensor/communication issues.
With scan tool, observe live NOx B data stream and heater status. Compare NOx B to NOx A and to expected behavior during cold/warm engine conditions.
Inspect the NOx B connector and harness along its full length for damage, corrosion, heat damage, or pin push-out. Repair any physical damage.
Verify power and ground at the sensor connector with engine off and running; check heater circuit for proper voltage and measure heater resistance. Replace sensor if heater open or out of spec.
Check CAN/communication integrity: look for network errors, lost messages, and verify proper termination resistances. Wiggle test harness while watching for bus error increases.
If wiring and power/ground are good, bench-test or substitute a known-good NOx sensor B (or swap with an identical sensor where practical and safe) to confirm diagnosis.
If replacing sensor does not clear the issue, trace communications to the ECM/PCM, check for multiple modules reporting related faults, and consider ECM/PCM reflash or replacement only after verifying harness and other modules.
Clear codes and perform a road/regen cycle to confirm repair; monitor for return of the code.

Likely causes

Wiring or connector problem between NOx sensor B and powertrain module
Failed or degraded NOx sensor B (heater or sensing element)
CAN/communication bus errors preventing valid NOx B data
ECM/PCM software or module-level fault after recent repair or reflash

Fault status

⚠️ Status

U05A2 — NOx Sensor B received invalid data from ECM/PCM. Indicates communication or signal fault affecting the NOx B measurement stream (sensor, wiring, bus, or module/software).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours