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P11FC GMC Code - O2 Low Reference Circuit (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
P11FC GMC indicates O2 Low Reference Circuit (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 409
How popular is this code, among other codes? Low
What is this?
Table of contents Created and updated by William Orellana on Mar 24, 2024
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Code P11FC GMC 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 P11FC GMC - O2 Low Reference Circuit (NOx Sensor 2) - AutoCodes.com
P11FC GMC Code - O2 Low Reference Circuit (NOx Sensor 2)
What does this mean?

What are the Possible Causes of the DTC P11FC GMC?

  • 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 P11FC GMC?

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 P11FC GMC 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 P11FC GMC code?

Need more information on how to fix the P11FC GMC code? Get Access to Factory Service Manuals

Need Help with the Code?

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Information for Specific GMC Models

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 P11FC GMC Code

What does the OBDII code P11FC mean for my GMC vehicle?

The OBDII code P11FC indicates a low reference circuit issue related to the NOx sensor 2, which monitors nitrogen oxide levels in the exhaust system.

What are the common symptoms of a P11FC code?

Common symptoms include illuminated check engine light, poor fuel economy, increased emissions, and potential rough idling or performance issues.

What could cause the P11FC code to trigger?

Causes may include a faulty NOx sensor 2, damaged wiring or connectors in the sensor circuit, or issues with the engine control module (ECM).

How can I diagnose a P11FC code?

To diagnose a P11FC code, inspect the NOx sensor 2 and its wiring for damage, check the sensor’s voltage and resistance values, and use a scan tool to monitor live data.

Can I drive my GMC with a P11FC code?

While it may be possible to drive your vehicle, it’s not recommended as it can lead to decreased performance and increased emissions, and may cause further damage.

What are some repair tips for fixing a P11FC code?

Repair tips include checking and repairing any damaged wiring, replacing the faulty NOx sensor 2, and ensuring that the ECM is functioning properly.

Will clearing the P11FC code fix the issue temporarily?

Clearing the code may temporarily turn off the check engine light, but the underlying issue will likely cause the code to return if not properly addressed.

How much does it typically cost to repair a P11FC code?

Repair costs can vary widely, but replacing a NOx sensor generally ranges from $100 to $300, depending on labor and parts.

Is there a way to prevent a P11FC code from occurring?

Regular maintenance, including timely replacement of exhaust components and sensors, can help prevent issues that may lead to a P11FC code.

Discuss the causes and fixes for P11FC GMC OBDII Code

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