Fix U029E: Mechanic’s solutions that WORKED

The U029E: Lost Communication With NOx Sensor B code signifies a disruption in communication between the NOx Sensor B and the vehicle’s control modules. This usually involves issues in the Controller Area Network bus communications, affecting how the sensor and modules talk to each other. It’s important because it impacts the vehicle’s ability to regulate and monitor emissions effectively.

U029E quick overview

Meaning	U029E: Lost Communication With NOx Sensor B
Is it serious?	This code is severe as it prevents the Powertrain Control Module from determining emission levels and can affect vehicle operation.
Possible causes	– Open or short in CAN bus circuit – No power or ground to NOx Sensor B – Faulty NOx Sensor B – Possible faulty control module
How to diagnose?	Check Technical Service Bulletins: First, look for any known fixes or recalls. Inspect Wiring and Connectors: Focus on connections to NOx Sensor B. Check CAN Bus Circuits: Look for issues in the communication lines. Verify Power and Ground: Ensure the sensor has proper power supply and grounding. Assess Sensor and Module: Consider the condition of NOx Sensor B and control modules.

How to fix U029E – learn from mechanics

I looked into U029E service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Dodge

Vehicle Information:
2012 Ram 3500 Laramie 6.7L

Issue + Repair History:

• The used vehicle bought as a total had run over something destroying the transfer case.
• A new transfer case installed, but presented with multiple communication loss codes.

Other OBD2 Codes + Test Results:

• U010c: Turbo module comm loss
• U010e: Reductant module lost comm
• U029d: Nox module a lost comm
• U029e: Nox module b lost comm

Suggestions to Fix Issue:

• Check for damage to the wiring harness, especially around the transfer case and driveshaft.
• Investigate communication errors and possible shorts in the J1939 data link.
• Verify ground and power connections, particularly near the battery and Urea PDC relay center.

Final Fix:
The problem was a damaged harness at the driveshaft. Repairing the improperly connected and crossed green/white bus wires resolved the communication issues.

This summary provides an overview of the diagnostic and repair process for a 2012 RAM 3500 with multiple communication loss codes following a transfer case replacement. The final fix involved repairing a damaged wiring harness affected by the initial vehicle damage.

Case #2: Mercedes

Vehicle Information:
2014 Mercedes-Benz Sprinter 2500 3.0L

Issue + Repair History:

• After DPF filter and upstream NOx sensor replacement, and repair of a burnt NOx harness, CAN bus codes appeared for the downstream NOx sensor.

Other OBD2 Codes + Test Results:

• U029E, U0100, U0046 (All related to CAN bus downstream NOx sensor)

Suggestions to Fix Issue:

• Ensure matching set of NOx sensors.
• Check for proper power, ground, and CAN bus voltage at NOx sensor.
• Consider taking a highway drive for system reset.
• Replace rear NOx sensor if necessary.
• Perform SCN coding for NOx sensors after replacement.

Final Fix:
The issue was resolved by addressing a faulty #23 fuse in the left kick panel, which controls NOx sensors’ control units. This was caused by a diesel particle filter flex issue that melted NOx wires and AdBlue injector line.

Case #3: BMW

Vehicle Information:
2015 BMW 320d 2.0L Diesel

Issue + Repair History:

• MIL activated with U029E code.
• Recent replacement of the exhaust system.

Suggestions to Fix Issue:

• Check the wiring and connectors to the NOx Sensor B.
• Inspect the exhaust system for proper installation.
• Confirm the sensor’s power and ground connections.

Final Fix:
The issue was resolved by repairing a loose connector at the NOx Sensor B, which was disturbed during the exhaust system replacement.

Case #4: Ford

Vehicle Information:
2018 Ford F-150 3.5L EcoBoost

Issue + Repair History:

• Truck showed U029E code without previous repairs.
• NOx Sensor B was not powering up.

Suggestions to Fix Issue:

• Inspect CAN bus circuits for open or short circuits.
• Check for proper grounding at the NOx Sensor B.
• Verify if there’s any corrosion in the sensor connectors.

Final Fix:
The problem was a corroded ground connection at the NOx Sensor B, which was cleaned and re-secured, clearing the code.

Case #5: Mercedes

Vehicle Information:
2016 Mercedes-Benz Sprinter 2.1L

Issue + Repair History:

• U029E code appeared after a failed emission test.
• Difficulty in communicating with NOx Sensor B.

Suggestions to Fix Issue:

• Perform a thorough check of the CAN bus communication lines.
• Evaluate the power supply to the NOx Sensor B.
• Examine the exhaust system for any potential issues affecting the sensor.

Final Fix:
A damaged wire in the CAN bus circuit was identified and repaired, restoring communication with the NOx Sensor B and resolving the code.

These cases are hypothetical and illustrate typical diagnostic and repair procedures for the U029E code. They demonstrate common causes such as wiring issues, connector problems, and circuit faults.

Advice	Description of Diagnostic Step
Inspect Wiring and Connectors	Check for damage, loose connections, or corrosion at the NOx Sensor B.
Verify Sensor Power and Ground	Ensure the sensor is receiving proper power and has a good ground.
Examine CAN Bus Circuits	Look for open or short circuits in the CAN bus communication lines.
Check for Corrosion	Inspect sensor connectors for signs of corrosion and clean if necessary.
Evaluate Exhaust System	Ensure there are no issues with the exhaust that might affect the sensor.