B0940 - Understanding DTC B0940: Common Issues in 2015-2018 Honda Accord and Toyota Camry

Quick Answer

B0940 means: B0940 indicates a malfunction in the rear window defogger circuit managed by the BCM.

Fix: Check and replace faulty components Cost: $300 - $800 Time: 90-180 minutes

Can I drive with B0940? Address this issue promptly to ensure visibility and prevent further electrical problems.

Common Questions

What does B0940 mean and how does it affect my car?

The B0940 code indicates a problem with the rear window defogger circuit managed by the BCM. This can lead to visibility issues, especially in wet or cold conditions, as the rear window may not clear effectively, impacting safety.

What are the most common causes of B0940 and how much does it cost to fix?

The most common causes of B0940 include a faulty BCM (60%), damaged wiring (25%), and blown fuses (10%). Repair costs can range from $10 for a fuse replacement to $800 for BCM replacement, depending on the specific issue.

Can I drive my car with B0940 or should I stop immediately?

While you can drive with the B0940 code, it is advisable to address it quickly to ensure rear visibility, especially in inclement weather. Ignoring it may lead to further electrical issues.

How can I diagnose B0940 myself using GeekOBD APP?

You can use the GeekOBD APP to scan for DTCs and retrieve freeze frame data. This will help you analyze the conditions under which the B0940 code was triggered and guide you in further diagnostics.

What vehicles are most commonly affected by B0940?

The B0940 code frequently appears in models like the 2015-2018 Honda Accord and Toyota Camry. Always check for any recalls or Technical Service Bulletins (TSBs) related to your specific vehicle.

How can I prevent B0940 from happening again?

Regularly inspect electrical connections for corrosion and wear, especially in areas exposed to moisture. Ensure that your vehicle's software is updated, as this can prevent rare software-related issues.

What is B0940?

The Diagnostic Trouble Code (DTC) B0940 indicates a fault in the vehicle's body control module (BCM) related to the rear window defogger circuit. This code is prevalent in various makes and models, particularly in vehicles like the 2015-2018 Honda Accord and Toyota Camry. When this code appears, it usually signifies that the BCM has detected a malfunction in the circuit responsible for controlling the rear defogger. This could lead to the rear window not defogging properly, which can be particularly problematic in cold or humid conditions. Drivers may notice reduced visibility and may find themselves needing to manually clear the rear window, which can pose safety risks. In the long run, ignoring this code can lead to further electrical issues within the vehicle, as the BCM controls various other functions. Addressing the B0940 code promptly can help ensure that your vehicle's electrical systems remain functional and reliable.

System: B - Body (Airbags, Lighting, Security, Climate Control)

Symptoms

Common symptoms when B0940 is present:

  • The rear window defogger fails to operate, leaving the glass fogged up in cold weather, which compromises visibility.
  • Check Engine Light (CEL) or similar warning lights may illuminate, indicating that the BCM has logged the B0940 code.
  • Intermittent electrical issues may occur, such as malfunctioning of other features controlled by the BCM, like door locks or interior lights.
  • Increased difficulty in clearing the rear window, especially in humid or cold conditions.
  • Potential for related codes to appear, indicating broader electrical issues within the vehicle.

Possible Causes

Most common causes of B0940 (ordered by frequency):

  1. A faulty body control module (BCM) is the most common cause, accounting for around 60% of B0940 instances. This may be due to a manufacturing defect or wear over time.
  2. Damaged wiring or connectors in the rear window defogger circuit can lead to poor electrical connections, making up about 25% of cases. Corrosion or physical damage should be inspected.
  3. A blown fuse for the rear defogger circuit can also trigger the B0940 code. It's advisable to check the fuse box and replace any blown fuses to prevent future issues.
  4. Less common but serious causes include short circuits in the BCM, which can result from water ingress or other electrical faults.
  5. Rarely, software issues in the BCM can cause the system to misinterpret the status of the rear defogger circuit.

B0940 Repair Costs

Cost Breakdown by Repair Type

BCM Replacement

Replacing the body control module due to malfunction.

  • Total: $300 - $800
  • Success rate: 85%
Wiring Repair

Repairing damaged wiring or connectors in the rear defogger circuit.

  • Total: $100 - $300
  • Success rate: 90%
Fuse Replacement

Replacing a blown fuse for the rear defogger circuit.

  • Total: $10 - $50
  • Success rate: 95%
Money-Saving Tips for B0940
  • Start with the most common and least expensive repairs first
  • Use GeekOBD APP to confirm diagnosis before replacing expensive parts
  • Consider preventive maintenance to avoid future occurrences
  • Compare prices for OEM vs aftermarket parts based on your needs
  • Address the issue promptly to prevent more expensive secondary damage

Diagnostic Steps

Professional B0940 Diagnosis Process

Follow these systematic steps to accurately diagnose B0940. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion around the rear defogger circuit (5-10 minutes)

Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion around the rear defogger circuit (5-10 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context, focusing on related codes that may provide further insight (10-15 minutes)

Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context, focusing on related codes that may provide further insight (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 3: Step 3: Component testing - Use a multimeter to test the BCM and the rear window defogger circuit for proper voltage and continuity (20-30 minutes)

Step 3: Component testing - Use a multimeter to test the BCM and the rear window defogger circuit for proper voltage and continuity (20-30 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 4: Step 4: System function test - After any repairs, verify proper operation of the rear defogger and clear codes to monitor for reoccurrence (10-15 minutes)

Step 4: System function test - After any repairs, verify proper operation of the rear defogger and clear codes to monitor for reoccurrence (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and check for any new codes that may appear (15-20 minutes)

Step 5: Road test verification - Drive the vehicle under various conditions to confirm repair success and check for any new codes that may appear (15-20 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.

Important Notes

  • Always verify the repair with GeekOBD APP after completing diagnostic steps
  • Clear codes and test drive to ensure the problem is resolved
  • Address underlying causes to prevent code recurrence

Real Repair Case Studies

Case Study 1: BCM Replacement in 2017 Honda Accord

Vehicle: 2017 Honda Accord, 50,000 miles

Problem: Customer reported that the rear window defogger was non-functional, leading to visibility issues.

Diagnosis: Using the GeekOBD APP, we retrieved the B0940 code and confirmed a faulty BCM during testing.

Solution: Replaced the body control module with a new part and reprogrammed it to sync with the vehicle's systems.

Cost: $600 (parts: $500 for BCM, $100 for labor)

Result: Post-repair, the rear defogger operated correctly, and the customer reported no further issues.

Case Study 2: Wiring Repair in 2016 Toyota Camry

Vehicle: 2016 Toyota Camry, 40,000 miles

Problem: Rear window defogger failure prompted a check engine light.

Diagnosis: Diagnostic steps revealed damaged wiring in the defogger circuit, triggering the B0940 code.

Solution: Repaired the damaged wiring and ensured proper insulation to prevent future issues.

Cost: $200 (parts: $50 for wiring, $150 for labor)

Result: The rear defogger function was restored, and the check engine light was cleared.

Diagnose B0940

Use GeekOBD APP for professional diagnosis!

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  • Step-by-step repair guidance
  • Professional-grade analysis
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Code Information

Code: B0940
System: Body (Airbags, Lighting, Security, Climate Control)
Severity: MEDIUM
Category: Body Codes