OBD-II code family
Lost Communication With NOx Sensor (2 codes)
2 related fault descriptions. Use each full code and the exact vehicle service information to identify its circuit, monitored condition, and required tests.
Codes in this family
This is the complete published member list for this guide. Each code retains its own page; shared diagnostic context does not mean that every member has the same test or repair.
What these codes mean
U029D and U029E identify lost communication with the NOx sensors designated A and B. Keep the actual identifier: a technician must determine which participant the reporting controller expected to hear from. The letters do not supply a universal bank, exhaust position, component count or wiring layout.
Ford's 2023–2024 diesel OBD summary, revised August 25, 2023, provides a specific example on physical pages 107–108. The communication monitor expects the A or B sensor's master message. Missing communication is a different result from a received message with invalid data, a heater-circuit fault or an emissions-performance measurement. The missing message alone does not prove a failed sensing element or electronic unit.
Save the full multi-module scan, including status, any available suffix, companion faults and event information. Describe warnings and symptoms already observed. The reporting controller and installed network information determine which supply, connection, communication and component checks are appropriate. A partner code that is present or absent cannot by itself establish a shared failure or a healthy second circuit.
Have qualified personnel use the matched network procedure and protected equipment. Do not apply a generic bus-resistance number, probe unidentified pins, disconnect participants or swap sensors as a diagnostic experiment. Controller configuration, software or component replacement needs its own supporting findings and any required setup.
The useful next step is a demonstrated communication diagnosis and an itemized repair plan. Require verification of the relevant message exchange and original complaint after the established fault is repaired. A cleared code, one response or an ignition cycle alone does not establish completion. Follow the vehicle's actual warnings and handbook; these codes do not determine a safe distance, fallback mode or restart allowance.
Identify the circuit on your vehicle
Match the full DTC, reporting module, and any failure-type suffix to the service information for your exact year, make, model, engine, and equipment. An identifier alone does not establish installed hardware count, location, connector pinout, or a universal measurement.
Where the manufacturer publishes its own meaning for this code, that is the one to work from — it describes the actual component on your vehicle, which the generic definition cannot. Keep the generic description for what it is good for: it tells you which subject area the standard assigned the code to, which is useful context when the two appear to disagree. If they do disagree, follow the manufacturer.