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P11D9 2018 GMC Sierra Code - O2 Pump Current Control 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
P11D9 2018 GMC Sierra indicates O2 Pump Current Control 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 143
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 P11D9 2018 GMC Sierra 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 P11D9 2018 GMC Sierra - O2 Pump Current Control Circuit Low Voltage (NOx Sensor 2) - AutoCodes.com
P11D9 2018 GMC Sierra Code - O2 Pump Current Control Circuit Low Voltage (NOx Sensor 2)
What does this mean?

What are the Possible Causes of the DTC P11D9 2018 GMC Sierra?

  • 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 P11D9 2018 GMC Sierra?

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 P11D9 2018 GMC Sierra 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 P11D9 2018 GMC Sierra code?

Need more information on how to fix the P11D9 2018 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

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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 P11D9 2018 GMC Sierra Code

1. What does the OBDII code P11D9 mean on a 2018 GMC Sierra?

P11D9 indicates a low voltage issue in the O2 pump current control circuit for NOx Sensor 2, which monitors nitrogen oxide emissions.

2. What are the common symptoms of the P11D9 code?

Symptoms may include an illuminated check engine light, reduced engine performance, poor fuel efficiency, or increased exhaust emissions.

3. What causes the P11D9 code to appear?

Common causes include a faulty NOx sensor, damaged wiring or connectors, a failed O2 pump, or issues with the Engine Control Module (ECM).

4. Can I drive my 2018 GMC Sierra with the P11D9 code?

Driving with this code is not recommended, as it may lead to reduced engine performance and increased emissions, potentially causing further damage.

5. How do I diagnose the P11D9 code on a 2018 GMC Sierra?

Diagnose by inspecting the wiring and connectors for damage, testing the NOx sensor and O2 pump, and using a scan tool to check related live data.

6. How do I fix the P11D9 code?

Repairs may involve replacing the NOx sensor, repairing damaged wiring, or addressing ECM issues if the sensor and wiring are functional.

7. How much does it cost to repair the P11D9 code?

Repair costs vary but typically range from $200 to $600, depending on whether the NOx sensor or wiring needs replacement.

8. Can a faulty NOx sensor cause other issues in my GMC Sierra?

Yes, a faulty NOx sensor can lead to increased emissions, reduced fuel efficiency, and potential damage to other emissions-related components.

9. Is the P11D9 code covered under warranty for my 2018 GMC Sierra?

It may be covered under the emissions warranty; check with your GMC dealer for specific warranty details.

10. How can I prevent the P11D9 code from occurring again?

Regular maintenance, inspecting wiring for damage, and using high-quality fuel can help prevent recurrence of the P11D9 code.

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