AutoCodes – Generic – P11FD

P11FD Code - O2 Low Reference Circuit Low Voltage (NOx Sensor 2)

Quick Answer

The Nitrogen Oxides (NOx) sensors are part of the selective catalytic reduction system, a device used to reduce NOx emission on diesel engines. Common causes include Faulty Nitrogen Oxides (NOx) Sensor 2, Nitrogen Oxides Sensor 2 harness is open or shorted, Nitrogen Oxides Sensor 2 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: P11FD indicates O2 Low Reference Circuit Low Voltage (NOx Sensor 2).
Common causes: Common causes include Faulty Nitrogen Oxides (NOx) Sensor 2, Nitrogen Oxides Sensor 2 harness is open or shorted, Nitrogen Oxides Sensor 2 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 814

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Mar 24, 2024

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P11FD Description

The Nitrogen Oxides (NOx) sensors are part of the selective catalytic reduction system, a device used to reduce NOx emission on diesel engines. There are two NOx sensors, one placed upstream of selective catalytic reduction, to measure inlet NOx concentration, and one placed downstream. They are connected with the control module via CAN and all the information is exchanged through it. Since it is a smart sensor, all the electrical monitoring is performed inside the sensor and only the results are sent to the Engine Control Module (ECM). 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 the 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 (reductant) added by varying the reductant injector duty cycle in response to changes in engine exhaust 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. The Diagnostic Trouble Code (DTC) will be set if the ECM software detects a fault in the NOx sensor circuitry or a performance fault in the NOx sensor for greater than 2 s.

OBDII Code P11FD - O2 Low Reference Circuit Low Voltage (NOx Sensor 2) - AutoCodes.com — P11FD Code - O2 Low Reference Circuit Low Voltage (NOx Sensor 2)

What does this mean?

What are the Possible Causes of the DTC P11FD?

Faulty Nitrogen Oxides (NOx) Sensor 2
Nitrogen Oxides Sensor 2 harness is open or shorted
Nitrogen Oxides Sensor 2 circuit poor electrical connection

How to Fix the DTC P11FD?

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 P11FD 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.

Need more information about the P11FD code?

Need more information on how to fix the P11FD code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P11FD code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

P11FD Buick — O2 Low Reference Circuit Low Voltage (NOx Sensor 2)
P11FD Cadillac — O2 Low Reference Circuit Low Voltage (NOx Sensor 2)
P11FD Chevrolet — O2 Low Reference Circuit Low Voltage (NOx Sensor 2)
P11FD GMC — O2 Low Reference Circuit Low Voltage (NOx Sensor 2)

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 P11FD Code

1. What does OBDII code P11FD mean?

P11FD indicates a problem with the low reference circuit of NOx Sensor 2, where the voltage is lower than expected.

2. What are the common symptoms of code P11FD?

Symptoms may include the Check Engine Light turning on, reduced fuel efficiency, poor engine performance, or failed emissions tests.

3. What causes the P11FD code to appear?

Common causes include a faulty NOx Sensor 2, damaged wiring or connectors in the low reference circuit, or an issue with the engine control module (ECM).

4. Can driving with code P11FD cause damage?

Driving with P11FD for extended periods can lead to increased emissions, reduced performance, and potential damage to the catalytic converter.

5. How is code P11FD diagnosed?

A technician diagnoses P11FD by using a scan tool to check live data, inspecting the wiring and connectors, and testing the NOx sensor for proper function.

6. Is replacing the NOx sensor necessary to fix P11FD?

Not always; the issue could be related to wiring or connectors. The sensor should only be replaced if testing confirms it is faulty.

7. How much does it typically cost to repair code P11FD?

The cost can range from $200 to $800, depending on whether the issue is with the sensor, wiring, or ECM.

8. Can a dirty or clogged NOx sensor cause code P11FD?

No, this code specifically relates to a low voltage issue in the low reference circuit, not a clogged or dirty sensor.

9. How can I prevent code P11FD from recurring?

Regular maintenance, inspecting wiring for damage, and ensuring the NOx sensor is functioning properly can help prevent this code.

10. Will clearing the P11FD code solve the problem?

Clearing the code may temporarily turn off the Check Engine Light, but the underlying issue must be fixed to prevent the code from returning.

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