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AutoCodes – GMC – P1194 2018 GMC Sierra

P1194 2018 GMC Sierra Code - O2 Low Reference Circuit High Voltage (NOx Sensor 1)

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, Nitrogen Oxides Sensor harness is open or shorted, Nitrogen Oxides Sensor 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
P1194 2018 GMC Sierra indicates O2 Low Reference Circuit High Voltage (NOx Sensor 1).
Common causes
Common causes include Faulty Nitrogen Oxides (NOx) Sensor, Nitrogen Oxides Sensor harness is open or shorted, Nitrogen Oxides Sensor 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 169
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 P1194 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 P1194 2018 GMC Sierra - O2 Low Reference Circuit High Voltage (NOx Sensor 1) - AutoCodes.com
P1194 2018 GMC Sierra Code - O2 Low Reference Circuit High Voltage (NOx Sensor 1)
What does this mean?

What are the Possible Causes of the DTC P1194 2018 GMC Sierra?

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

How to Fix the DTC P1194 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 P1194 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 P1194 2018 GMC Sierra code?

Need more information on how to fix the P1194 2018 GMC Sierra code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P1194 2018 GMC Sierra code diagnosed by a professional: Find a repair shop in your area

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 P1194 2018 GMC Sierra Code

1. What does the OBDII code P1194 mean on a 2018 GMC Sierra?

P1194 indicates an issue with the O2 Low Reference Circuit High Voltage for NOx Sensor 1, meaning the sensor is detecting higher-than-expected voltage in the reference circuit.

2. What are the common symptoms of the P1194 code in a 2018 GMC Sierra?

Symptoms may include the check engine light turning on, reduced fuel efficiency, poor engine performance, or the vehicle entering limp mode.

3. What causes the P1194 code in a GMC Sierra?

Common causes include a faulty NOx sensor, damaged wiring or connectors, corrosion in the circuit, or a malfunctioning ECM.

4. Can a faulty NOx sensor cause the P1194 code?

Yes, a malfunctioning NOx sensor is a primary cause of this code, as it may send incorrect voltage signals to the ECM.

5. How do I diagnose the P1194 code in a 2018 GMC Sierra?

Diagnose by using a scan tool to confirm the code, inspecting the wiring and connectors for damage or corrosion, and testing the NOx sensor and reference circuit voltage.

6. Is it safe to drive with a P1194 code on my 2018 GMC Sierra?

While the vehicle may still be drivable, it can suffer from reduced performance or fuel efficiency, and ignoring the issue could lead to further damage.

7. How do I fix the P1194 code on a GMC Sierra?

Repairs may involve replacing the NOx sensor, repairing or replacing damaged wiring, cleaning corroded connectors, or reprogramming the ECM if necessary.

8. What tools are needed to fix the P1194 code?

You’ll need an OBDII scan tool, a multimeter for electrical testing, and possibly basic hand tools to remove and replace the NOx sensor.

9. How much does it cost to repair the P1194 code on a 2018 GMC Sierra?

Repair costs vary, but replacing a NOx sensor can cost between $300 and $800, depending on labor and parts availability.

10. Can a software update fix the P1194 code?

In some cases, an ECM software update may resolve the issue if the problem is related to a programming error or calibration issue.

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