B2104 code definition
The B2104 trouble code signals a passenger door key cylinder switch failure.
What the B2104 code means
The B2104 code is a standard OBD-II body trouble code that detects a failure in the passenger door key cylinder switch. The passenger door key cylinder switch allows the front passenger door to be manually locked and unlocked using the key. This cylinder switch is attached to the door lock, which is located on the exterior of the front passenger door, directly next to the door handle. When the key is inserted into the door lock and rotated, the key cylinder switch locks or unlocks the passenger door. If the passenger door key cylinder switch fails, the body control module will likely report the B2104 trouble code.
What causes the B2104 code?
There is only one common cause of the B2104 trouble code, and that’s a failed passenger door key cylinder switch. The cylinder switch is made up of multiple components, and any one of these components can fail, though the switch will need to be replaced regardless. In extremely uncommon cases, the code will be stored due to a malfunctioning body control module.
What are the symptoms of the B2104 code?
If the B2104 trouble code is stored, then it is likely that the passenger door key lock and unlock system will fail, meaning the passenger door will not be able to be unlocked or locked using the key and exterior lock. This code may also be joined by an illuminated check engine soon Warning Light on the gauge cluster.
How does a mechanic diagnose the B2104 code?
The B2104 code should first be diagnosed with a standard OBD-II trouble code scanner. It may appear that the scanner is unnecessary with this code, and that a manual check is all that is required, but using the scanner allows the mechanic to check the status of the body control module, and also see if any other trouble codes have been detected. If there are multiple codes present, then the technician will need to address them in the order in which they are displayed on the scanner. The trouble codes will then be reset, the vehicle restarted, and the B2104 code checked for. If the trouble code is no longer present, and the passenger door key lock system is fully functional, then the code likely represents an intermittent issue, or was inaccurately detected.
If the B2104 code is still present, then the passenger door key cylinder switch will need to be replaced. After replacement, the codes should again be reset, the vehicle again restarted, and the code again checked for. If the code persists, then it should be assumed that the body control module has failed.
Common mistakes when diagnosing the B2104 code
The most frequently made mistake when diagnosing this code is the failure to observe the OBD-II trouble code diagnosis protocol. The diagnosis protocol should always be complied with, as it helps guarantee thorough inspections.
Often the passenger door key cylinder switch is replaced without the trouble codes ever being checked with a code scanner. If this mistake is made, potential problems elsewhere in the vehicle will go unnoticed.
How serious is the B2104 code?
A vehicle with the B2104 trouble code will still be drivable, and will not experience any drivability problems. The front passenger door will likely not be able to be locked or unlocked using the key, which can cause practicality and security concerns. It’s a good idea to have the vehicle inspected when the code is detected.
What repairs can fix the B2104 code?
This trouble code can almost always be fixed by replacing the passenger door key cylinder switch. In rare cases, the body control module may need to be replaced.
Additional comments for consideration regarding the B2104 code
This code is a manufacturer specific code. Manufacturer specific codes are codes that have varying definitions from automaker to automaker. In many vehicles, the B2104 code detects a passenger door key cylinder switch failure, but in some vehicles this code represents an entirely different body problem. As is always the case, the mechanic should take note of the vehicle that is being inspected when diagnosing this trouble code.
Need help with a B2104 code?
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This article originally appeared on YourMechanic.com as B2104 OBD-II Trouble Code: Door Passenger Key Cylinder Switch Failure and was authored by Brady Klopfer.