AutoCodes – GMC – B0408 2018 GMC Sierra

B0408 2018 GMC Sierra Code - Main Temperature Control Circuit

Quick Answer

Stepper motors are used for temperature regulation, air distribution control and recirculation door control. Common causes include Faulty Air Temperature Actuator, Air Temperature Actuator harness is open or shorted, Air Temperature Actuator 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: B0408 2018 GMC Sierra indicates Main Temperature Control Circuit.
Common causes: Common causes include Faulty Air Temperature Actuator, Air Temperature Actuator harness is open or shorted, Air Temperature Actuator 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 413

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 29, 2024

Description
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code B0408 2018 GMC Sierra Description

Stepper motors are used for temperature regulation, air distribution control and recirculation door control. With the switches and dials on the HVAC controls, air temperature door position, mode door position and recirculation door position can be selected. The selected values are passed to the Heating, Ventilation, and Air Conditioning (HVAC) Control Module via serial data. The HVAC control module supplies a 12 V reference voltage to the stepper motors and energizes the 4 stepper motor coils with a pulsed ground signal. The stepper motors move the appropriate doors into the calculated positions, in order to reach the desired positions.

OBDII Code B0408 2018 GMC Sierra - Main Temperature Control Circuit - AutoCodes.com — B0408 2018 GMC Sierra Code - Main Temperature Control Circuit

What does this mean?

What are the Possible Causes of the DTC B0408 2018 GMC Sierra?

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

How to Fix the DTC B0408 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 does this mean?

Code Tech Notes

B0413:02 Main Temperature Control Circuit Short to Ground
B0413:05 Main Temperature Control Circuit Short to Battery or Open
B0413:61 Main Temperature Control Circuit Actuator Stuck Open

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B0408 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 B0408 2018 GMC Sierra 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 B0408 2018 GMC Sierra Code

1. What are common symptoms of OBDII code B0408 in a 2018 GMC Sierra related to the Main Temperature Control Circuit?

- Common symptoms include inconsistent temperature control in the cabin, the heater or air conditioner not working properly, and the climate control system not responding correctly to temperature adjustments.

2. What are possible causes of OBDII code B0408 in a 2018 GMC Sierra?

- Possible causes include a faulty temperature control module, damaged wiring or connectors in the temperature control circuit, or a malfunctioning blend door actuator.

3. How can I diagnose OBDII code B0408 in a 2018 GMC Sierra?

- Diagnose the code by using a scan tool to retrieve the trouble codes, checking the temperature control module and blend door actuator for proper operation, and inspecting the wiring and connectors for any damage.

4. Can OBDII code B0408 in a 2018 GMC Sierra be fixed without professional help?

- Depending on the exact cause, some repairs related to this code, such as replacing a faulty blend door actuator or repairing damaged wiring, can be done at home if you have the necessary tools and knowledge.

5. Is it safe to continue driving a 2018 GMC Sierra with OBDII code B0408?

- It is not recommended to continue driving the vehicle with this code, as it can lead to discomfort due to improper temperature control and may cause further damage to the climate control system if left unresolved.

6. How much does it typically cost to repair OBDII code B0408 in a 2018 GMC Sierra?

- The cost of repairing this code can vary depending on the exact cause and whether professional help is needed. Repairs may range from a simple fix like replacing a fuse to a more complex repair involving the temperature control module.

7. Are there any preventative maintenance tips to avoid OBDII code B0408 in a 2018 GMC Sierra?

- To help prevent issues related to this code, it's recommended to regularly inspect the climate control system, address any abnormal temperature control issues promptly, and follow the manufacturer's maintenance schedule for your vehicle.

8. Can a DIY enthusiast reset OBDII code B0408 in a 2018 GMC Sierra without a scan tool?

- It is not advisable to attempt to reset this code without addressing the underlying issue, as simply clearing the code without fixing the root cause can lead to recurring problems with the climate control system.

9. Will OBDII code B0408 in a 2018 GMC Sierra cause the check engine light to illuminate?

- While this code may not always trigger the check engine light, it can still be stored in the vehicle's memory and affect the performance of the climate control system, prompting the need for diagnostics and repairs.

10. How long does it typically take to repair OBDII code B0408 in a 2018 GMC Sierra?

- The repair time for this code can vary based on the specific cause and complexity of the issue. Simple fixes may take a shorter time, while more intricate repairs could require additional time for diagnosis and part replacement.