AutoCodes – Mercury – U029D Mercury

U029D Mercury Code - Lost Communication With NOx Sensor A

Quick Answer

The reductant system uses two Nitrogen Oxide (NOx) sensors to monitor the amount of NOx in the engine's exhaust gas. Common causes include Faulty Nitrogen Oxide (NOx) Sensor Bank 'A', Nitrogen Oxide (NOx) Sensor Bank 'A' harness is open or shorted, Nitrogen Oxide (NOx) Sensor Bank 'A' circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: U029D Mercury indicates Lost Communication With NOx Sensor A.
Common causes: Common causes include Faulty Nitrogen Oxide (NOx) Sensor Bank 'A', Nitrogen Oxide (NOx) Sensor Bank 'A' harness is open or shorted, Nitrogen Oxide (NOx) Sensor Bank 'A' circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 502

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

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Table of contents Created and updated by William Orellana on Apr 07, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code U029D Mercury Description

The reductant system uses two Nitrogen Oxide (NOx) sensors to monitor the amount of NOx in the engine's exhaust gas. The first sensor is located at the outlet of the turbocharger and monitors the engine out NOx level. The second NOx sensor is located between the Selective Catalytic Reduction (SCR) and the Diesel Particulate Filter (DPF) and monitors NOx levels downstream of the SCR. The second NOx sensor also provides the Engine Control Module (ECM) with information on the exhaust oxygen level during DPF regeneration.
Each NOx sensor contains a sensing cell, a pumping cell, and a heater. A sample of exhaust gas passes through a diffusion gap between the sensing cell and the pumping cell. The NOx sensor maintains a constant reference voltage across the sensing cell. An electronic circuit within sensor controls the pump current through the pumping cell in order to maintain a constant voltage in the sensing cell. The amount of current required to maintain the reference voltage in the sensing cell is proportional to the concentration of NOx in the exhaust.
The ECM varies the amount of Diesel Exhaust Fluid (DEF) or reductant added by varying the reductant injector duty cycle in response to changes in engine exhaust out NOx levels. The smart NOx sensors consist of two components, the NOx module and the NOx sensor element that are serviced as a unit. A circuit or performance condition with a NOx sensor is detected by the NOx sensor module. The smart NOx sensor module communicates the condition to the ECM over the serial data line. The ECM sets a DTC when a serial data message is received from the NOx sensor module.

OBDII Code U029D Mercury - Lost Communication With NOx Sensor A - AutoCodes.com — U029D Mercury Code - Lost Communication With NOx Sensor A

What does this mean?

What are the Possible Causes of the DTC U029D Mercury?

Faulty Nitrogen Oxide (NOx) Sensor Bank 'A'
Nitrogen Oxide (NOx) Sensor Bank 'A' harness is open or shorted
Nitrogen Oxide (NOx) Sensor Bank 'A' circuit poor electrical connection

How to Fix the DTC U029D Mercury?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the U029D Mercury code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about U029D Mercury Code

1. What are the common symptoms of OBDII code U029D Mercury?

The common symptoms of code U029D include the Check Engine Light coming on, poor engine performance, and potential issues with emissions.

2. What are the possible causes of the U029D code indicating "Lost Communication With NOx Sensor A" in a Mercury vehicle?

Possible causes of this code may include a faulty NOx sensor, damaged wiring or connectors, a failed PCM (Powertrain Control Module), or software issues.

3. How can I diagnose the U029D code in my Mercury vehicle?

Diagnosing the U029D code typically involves using an OBDII scanner to retrieve the code, checking the wiring and connectors for any visible damage, and testing the NOx sensor and related components.

4. Can I continue driving my Mercury with the U029D code present?

It is generally not recommended to continue driving with the U029D code active, as it can potentially lead to further damage to the vehicle's emissions system and affect the engine performance.

5. How can I repair the U029D code in my Mercury?

Repairing the U029D code may involve replacing the faulty NOx sensor, repairing any damaged wiring or connectors, reprogramming the PCM, or seeking assistance from a qualified mechanic for further diagnosis.

6. Is it safe to clear the U029D code using an OBDII scanner?

While clearing the code may temporarily turn off the Check Engine Light, it is important to address the underlying issue causing the U029D code to prevent future problems with the vehicle.

7. What are the long-term effects of ignoring the U029D code in my Mercury?

Ignoring the U029D code can lead to increased emissions, potential damage to the catalytic converter, and overall decreased engine performance and fuel efficiency.

8. Can a DIY enthusiast easily fix the U029D code issue?

Depending on the DIY enthusiast's skill level and access to tools, some may be able to address the U029D code by replacing the NOx sensor or checking the wiring. However, complex diagnostics may require professional assistance.

9. How much does it typically cost to repair the U029D code in a Mercury?

The cost of repairing the U029D code can vary depending on the specific cause of the issue, the parts needed for replacement, and whether professional labor is required. It's recommended to obtain a quote from a trusted mechanic.

10. Will the U029D code affect my Mercury's emissions testing?

Yes, the U029D code can potentially cause your Mercury to fail emissions testing, as it indicates a problem with the NOx sensor and emissions control system. Addressing the code promptly is crucial for passing emissions tests.