What Does U029D Mean?
The powertrain control module cannot communicate with NOX Sensor A on the network. This sensor monitors nitrogen oxide emissions and is critical for diesel and some gasoline emission systems.
Common Causes
40%
NOX Sensor A internal failure or heater circuit malfunction
30%
Damaged wiring harness or corroded connector to NOX Sensor A
15%
Power supply failure to NOX Sensor A circuit
10%
CAN communication circuit fault between sensor and control module
5%
Control module software issue or sensor not programmed
Diagnostic Steps
1
Step 1: Visually inspect NOX Sensor A and connector for damage, exhaust leaks, or contamination
2
Step 2: Check power supply and ground circuits to NOX Sensor A using wiring diagram
3
Step 3: Measure resistance of sensor heater element (typically 2-10 ohms when cold)
4
Step 4: Verify CAN communication voltage at sensor connector if equipped with digital output
5
Step 5: Replace sensor if all circuits test good; perform sensor relearn procedure after installation
Estimated Repair Cost
$400 - $1,200
Parts + labor, varies by vehicle and location
The powertrain control module cannot communicate with NOX Sensor A on the network. This sensor monitors nitrogen oxide emissions and is critical for diesel and some gasoline emission systems.
The most common cause of U029D (Lost Communication With NOX Sensor "A") is: NOX Sensor A internal failure or heater circuit malfunction
Typical repair costs for U029D range from $400 to $1,200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle remains drivable but emission control system is compromised. May fail emissions testing and cause check engine light.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to U029D to identify the root cause.
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Quick Info
Category
Network
System
Emissions Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
