AutoCodes – GMC – B0178 GMC

B0178 GMC Code - Output Air Temperature Sensor 2 Circuit

Quick Answer

Air temperature sensors allow the Heating, Ventilation, and Air Conditioning (HVAC) Control Module to monitor the temperature of the discharge air in the HVAC ducts. Common causes include Faulty Output Air Temperature Sensor 2, Output Air Temperature Sensor 2 harness is open or shorted, Output Air Temperature Sensor 2 circuit poor electrical connection. Severity is Low - monitor the vehicle and repair when practical. The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.

What it means: B0178 GMC indicates Output Air Temperature Sensor 2 Circuit.
Common causes: Common causes include Faulty Output Air Temperature Sensor 2, Output Air Temperature Sensor 2 harness is open or shorted, Output Air Temperature Sensor 2 circuit poor electrical connection.
Severity: Low - monitor the vehicle and repair when practical.
Can I drive?: The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.

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Code Popularity 1,741

How popular is this code, among other codes? Low

Repair Importance Level

Low (Monitor) (1 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Mar 10, 2021

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code B0178 GMC Description

Air temperature sensors allow the Heating, Ventilation, and Air Conditioning (HVAC) Control Module to monitor the temperature of the discharge air in the HVAC ducts. The module applies 5 volts to internal input resistors that are connected to the signal circuits of the air temperature sensors. The module provides ground to the air temperature sensors through the low reference circuit. The HVAC control module monitors the voltage drops across the air temperature sensors and uses the inputs for automatic control calculations. When the duct air temperatures are cold, the resistances of the sensors are high and the voltage signals are high. When the duct air temperatures are hot, the resistances of the sensors are low and the voltage signals are low. The HVAC control module converts the voltage values to count values where 1 volt is approximately equal to 51 counts.

OBDII Code B0178 GMC - Output Air Temperature Sensor 2 Circuit - AutoCodes.com — B0178 GMC Code - Output Air Temperature Sensor 2 Circuit

What does this mean?

What are the Possible Causes of the DTC B0178 GMC?

Faulty Output Air Temperature Sensor 2
Output Air Temperature Sensor 2 harness is open or shorted
Output Air Temperature Sensor 2 circuit poor electrical connection
Faulty Heating, Ventilation, and Air Conditioning (HVAC) Control Module

How to Fix the DTC B0178 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 does this mean?

Code Tech Notes

B0178 05: Output Air Temperature Sensor 2 Circuit Short to Battery or Open
B0178 02: Output Air Temperature Sensor 2 Circuit Short to Ground

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B0178 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.

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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 B0178 GMC Code

1. What are common symptoms of OBDII code B0178 GMC (Output Air Temperature Sensor 2 Circuit)?

- Common symptoms include issues with the HVAC system, such as incorrect air temperature readings or inconsistent heating and cooling.

2. What can cause OBDII code B0178 GMC to trigger?

- The code B0178 is usually triggered by a malfunction in the output air temperature sensor 2 circuit, which may be caused by wiring faults, sensor failure, or issues with the HVAC control module.

3. How can I diagnose the cause of OBDII code B0178 GMC?

- Proper diagnosis involves checking the wiring connections, testing the output air temperature sensor 2, and using a scan tool to troubleshoot the HVAC system for any faults.

4. Is it safe to continue driving with OBDII code B0178 GMC active?

- While it is possible to drive with this code, it is recommended to address the issue promptly to avoid potential HVAC system malfunctions and discomfort while driving.

5. What are some repair tips for fixing OBDII code B0178 GMC?

- Repair tips include checking and repairing any damaged wiring, replacing the faulty output air temperature sensor 2, or reprogramming the HVAC control module if necessary.

6. Can a DIY enthusiast fix OBDII code B0178 GMC at home?

- Depending on the skill level and access to tools, DIY enthusiasts may be able to address this code by following repair guides and using diagnostic equipment to identify and correct the issue.

7. How much does it typically cost to repair OBDII code B0178 GMC at a mechanic or dealership?

- Repair costs can vary, but replacing the output air temperature sensor 2 and addressing related issues may range from $100 to $300 at a mechanic or dealership.

8. Are there any recalls related to OBDII code B0178 GMC for certain GMC models?

- It is advisable to check with GMC or the National Highway Traffic Safety Administration (NHTSA) for any recalls or service bulletins related to OBDII code B0178 in specific GMC models.

9. Will resetting the OBDII system clear OBDII code B0178 GMC?

- While resetting the OBDII system may temporarily clear the code, it is important to diagnose and address the underlying issue causing the B0178 code to prevent it from reoccurring.

10. How can I prevent OBDII code B0178 GMC from coming back after repair?

- To prevent the code B0178 from recurring, ensure proper installation of the new sensor, perform regular maintenance on the HVAC system, and address any underlying electrical issues affecting the sensor circuit.