U029D A module on the network stopped hearing the first (upstream) NOx sensor module

Lost communication with NOx sensor A

U029D in short

U029D means the engine computer lost communication with the first NOx sensor module in the diesel exhaust. Ford and GM bulletins name water in the sensor harness or connector, and owners report reduced speed and a derate. Have it checked soon, and stop if the truck loses power.

Diesel trucks use NOx sensors, each with a small module, to watch the exhaust. When the engine computer stops hearing the first sensor module, it stores U029D, and an owner of a 2021 Ford reads it as "lost comm with NOx sensor A". GM scan tools show a similar pair as NOx sensor 1 and 2.

Ford bulletins for 2017-2020 6.7L Super Duty trucks say water can get through the harness into the NOx sensor module connector, to be replaced with the harness. GM bulletin 17-NA-219 describes moisture past a torn or missing connector seal on the 2016-2018 Colorado, Silverado and related trucks.

Owners report "Exhaust Fluid Service" and "Reduced Speed" messages, a derate and, on one 2022 Silverado 2500, a loss of power and a battery that needed a jump.

Most likely causes

  1. Water or corrosion in the NOx sensor harness or connector

    Supported by vehicle data
    Why it ranks here
    Ford SSM 46268, TSB 18-2365 and TSB 20-2067 name water intrusion for U029D on 6.7L Super Duty trucks, and GM 17-NA-219 describes moisture past a damaged connector seal.
    What would change this
    Rises if the connector shows moisture, green corrosion or a torn seal. Falls if the connector is dry and the seal intact.

  2. Failed NOx sensor or sensor module

    Supported by vehicle data
    Why it ranks here
    A Silverado 2500 owner cleared the matching U029E, reduced speed and exhaust fluid messages by replacing a NOx sensor; Ford replaces the module with the harness when moisture is found.
    What would change this
    Rises if the connector is clean and the sensor does not answer on a scan tool. Falls if wiring is the fault.

  3. Power or network fault affecting several modules

    Possible — needs testing
    Why it ranks here
    A 2017 Silverado 2500 stored U029D with a string of other lost-communication and reductant codes, and a 2022 truck with active U029D and U029E needed a jump start.
    What would change this
    Rises when many unrelated codes appear together. Falls if only NOx sensor codes are stored.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all codes and note whether U029E, P2209 or P249D and reductant or particulate sensor codes are stored too.

    Low riskTool: scan tool

  2. Have the NOx sensor module connector and harness inspected for moisture, corrosion and a torn or missing seal.

    Best left to a shop

    Warning:The exhaust system is hot after driving; let it cool, and leave diesel emissions repairs to a shop.

Symptoms

  • Check engine light with a reduced speed message
  • Exhaust fluid service message
  • Power loss while driving Gets more serious: stop and have it checked.
  • Truck will not crank Gets more serious: stop and have it checked.

How to fix

On your vehicle

Ford

  • SSM 46268Status unverified

    6.7L Super Duty MIL with U029D and/or P2209

    2017f-250-super-duty, f-350-super-duty, f-450-super-duty · issued · NHTSA 10094636

    Water intrusion through the harness into the NOx sensor module connector; replace the harness and module if moisture is found. Only the NHTSA summary was read.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • TSB 18-2365Status unverified

    6.7L Super Duty MIL with U029D and/or P2209

    2017–2019f-250-super-duty, f-350-super-duty, f-450-super-duty · issued · NHTSA 10155443

    Same concern for 2017-2019; water intrusion is named. Only the NHTSA summary was read.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • TSB 20-2067Status unverified

    6.7L Super Duty MIL with U029D, U029E, P22A7 and/or P2209

    2017–2020f-250-super-duty, f-350-super-duty, f-450-super-duty · NHTSA 10187826

    Builds up to 10-Jun-2020; water intrusion is named. Only the NHTSA summary was read.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Chevrolet

  • 17-NA-219Status unverified

    MIL with P249D, P249E, U029D, U029E

    2016–2018colorado, express, silverado-1500, silverado-2500-hd, silverado-3500-hd · issued · NHTSA 10190267

    Moisture past a torn or missing seal in the NOx sensor harness connector. Only the NHTSA summary was read.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

GMC

  • 17-NA-219 (GMC)Status unverified

    MIL with P249D, P249E, U029D, U029E

    2016–2018canyon, sierra-1500, sierra-2500-hd, sierra-3500-hd · issued · NHTSA 10190267

    Same GM diagnostic tip as for Chevrolet. Only the NHTSA summary was read.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • U029EA module on the network stopped hearing the second (downstream) NOx sensor module

    Same system Supported by vehicle data

    U029E is the matching lost-communication code for the second NOx sensor module and the two are often stored together.

All Module network (CAN bus) communication codes

Sources and review

  1. NHTSA complaint ODI 11282684: 2014 Chevrolet Silverado 2500 — NHTSA (owner complaint)
  2. NHTSA complaint ODI 11600634: 2017 Chevrolet Silverado 2500 — NHTSA (owner complaint)
  3. GM 17-NA-219 (NHTSA 10190267): MIL with P249D, P249E, U029D, U029E — NHTSA (manufacturer communication)
  4. NHTSA complaint ODI 11603488: 2022 Chevrolet Silverado 2500 — NHTSA (owner complaint)
  5. NHTSA complaint ODI 11678590: 2021 Ford F-250 Super Duty — NHTSA (owner complaint)
  6. Ford SSM 46268 (NHTSA 10094636): 2017 Super Duty 6.7L MIL with U029D and/or P2209 — NHTSA (manufacturer communication)
  7. Ford TSB 18-2365 (NHTSA 10155443): 2017-2019 Super Duty 6.7L MIL with U029D and/or P2209 — NHTSA (manufacturer communication)
  8. Ford TSB 20-2067 (NHTSA 10187826): 2017-2020 Super Duty 6.7L MIL with U029D, U029E, P22A7 and/or P2209 — NHTSA (manufacturer communication)
  9. NHTSA complaint ODI 11599344: 2017 Chevrolet Silverado 2500 — NHTSA (owner complaint)
Last reviewed
Written by
Saurabh K.
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