B2109 OBD-II Trouble Code: Heated Windshield Relay Short to Vbatt

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Cost of diagnosing the B2109 code

B2109 is a diagnostic trouble code (DTC) for "Heated Windshield Relay Short to Vbatt". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $79.99. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
Ford$79.99$20.00
Toyota$79.99$20.00
BMW$79.99$20.00
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B2109 code definition

The B2109 trouble code detects a problem with the heated windshield relay.

What the B2109 code means

The B2109 code is a standard OBD-II body trouble code that notes a heated windshield relay issue. Vehicles that have heated windshields do so as a more efficient means of defrosting the windshield than the standard defroster. When the defroster is turned on, small wires on the windshield will heat the glass to help remove any condensation, frost, or light moisture. If the climate control module notes that the heated windshield system is not functioning properly, then the B2109 trouble code may be stored.

What causes the B2109 code?

The B2109 trouble code can be caused by a few different things, such as:

  • Defective or shorted heated windshield relay
  • Damaged heated windshield wires
  • Damaged electrical components, notably blown fuses
  • In rare cases, a defective climate control module

What are the symptoms of the B2109 code?

When the B2109 code is stored, the front windshield defroster may not operate properly or at all. It is also possible that the code will be accompanied by an illuminated check engine soon Warning Light or a flashing climate control light.

How does a mechanic diagnose the B2109 code?

The B2109 code should be diagnosed using a standard OBD-II trouble code scanner. A trustworthy technician will use the scanner to view the freeze frame data and gather information about the B2109 code, while also checking to see if any additional trouble codes are present. If there are numerous codes present, then the mechanic should address them in the order that the scanner displays them in. The trouble codes should then be reset, the vehicle restarted, and the B2109 code checked for. If the code is no longer present, then it was likely inaccurately detected, or the result of an intermittent issue.

If the B2109 code remains detected, then the technician will begin by inspecting the base electrical components in the heated windshield system, and replacing any shorted wires, open connectors, or blown fuses. The wires responsible for heating the windshield should then be inspected, followed by the heated windshield relay.

After the mechanic replaces or repairs any part, the codes will once again be reset, the vehicle again restarted, and the code searched for. By doing this, the mechanic will know as soon as the issue is fully resolved.

Common mistakes when diagnosing the B2109 code

The most frequently made error when diagnosing the B2109 code comes from a failure to fully observe the OBD-II trouble code diagnosis protocol. The diagnosis protocol should be complied with at all times, to increase the odds of an efficient inspection and repair.

Heated windshield relays are commonly condemned even when they are working properly, because a blown fuse was not noticed.

How serious is the B2109 code?

The B2109 code will not keep a car from being drivable, and will not result in any drivability issues. However, the heated windshield will likely not work, which means the defroster will likely not work, which can cause dangerous visibility concerns. As soon as this code is detected, an inspection should be scheduled.

What repairs can fix the B2109 code?

Repairs for the B2109 trouble code include:

  • Replacement of fuses and other electrical components
  • Replacement of heated windshield wires
  • Replacement of the heated windshield relay
  • In very rare cases, replacement of the climate control module

Additional comments for consideration regarding the B2109 code

The B2109 code is a manufacturer specific trouble code. Manufacturer specific codes are codes that have varying definitions from automaker to automaker. While this code represents a heated windshield relay error in many cars, it represents an entirely different body problem in some vehicles.

Need help with a B2109 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

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