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B1978 OBD-II Trouble Code: Passenger’s Front Seat Down Switch Circuit Short to Battery

diagnostic check engine light

B1978 code definition

The B1978 trouble code detects a circuit error from the passenger front seat down switch.

What the B1978 code means

The B1978 code is a standard OBD-II trouble code that signals a passenger front seat down switch circuit problem. The passenger front seat down switch is used to control the height of the passenger seat cushion front. When this switch is pressed, the front of the seat cushion is lowered, which adjusts the angle to help the passenger find comfort. This switch is usually placed on the outboard side of the front passenger seat. If a passenger front seat down switch circuit error is noted by the body control module or powertrain control module (PCM), then the B1978 trouble code may be detected.

What causes the B1978 code?

The B1978 trouble code is usually caused by one of two things. The first is damaged electrical components in either the passenger front seat down switch, or the power seat system. The second is a malfunctioning passenger front seat down switch. The B1978 code can also be triggered by a defective body control module, though this is very rare and should not be assumed unless all other potential causes have been ruled out.

What are the symptoms of the B1978 code?

The B1978 trouble code will likely keep the front of the passenger seat cushion from being adjusted downwards, and likely upwards as well. It is also fairly common for this code to be accompanied by an illuminated check engine soon warning light on the gauge cluster.

How does a mechanic diagnose the B1978 code?

The B1978 code will be diagnosed using a standard OBD-II trouble code scanner. A reputable technician will use the scanner to assess the code by looking at the freeze frame data. The scanner will also be used to see if there are any additional trouble codes detected. If there are, they should be assessed in the order that they are displayed in. The trouble codes should then be reset, the vehicle restarted, and the B1978 code searched for. If the code is no longer detected, then it was likely detected inaccurately, or is the result of an intermittent issue.

If the code is still present, then the mechanic will visually inspect all of the electrical parts in the passenger front seat down switch and power seat systems. Any shorted wires, blown fuses, or open or corroded connectors will need to be replaced. If the electrical system is in good working condition, then it the passenger front seat down switch has likely failed.

After any replacements or repairs are made, the trouble codes will again be reset, the vehicle restarted, and the B1978 code checked for. This allows the mechanic to know when the problem has been fixed.

Common mistakes when diagnosing the B1978 code

The most frequently made error when diagnosing the B1978 code comes from a failure to follow the OBD-II diagnosis protocol. It is very important that technicians always adhere to the diagnosis protocol, as it greatly increases the chances of accurate repairs.

It is fairly common for electrical failures to be overlooked, which often results in unnecessary passenger front seat down switch replacements.

How serious is the B1978 code?

A vehicle with a B1978 trouble code will not have any drivability problems. However, the front of the passenger seat cushion will likely not be able to adjust, which can cause comfort and practicality issues for the passenger. As is the case with all trouble codes, when the B1978 code is detected, an inspection should be scheduled.

What repairs can fix the B1978 code?

Possible repairs for the B1978 trouble code are:

Additional comments for consideration regarding the B1978 code

The B1978 trouble code is a manufacturer specific code, which means that the definition of the code changes from automaker to automaker. While this code commonly signals a passenger front seat down circuit error, it can detect a very different body problem in many other cars. It’s important for mechanics to be aware of what make and model they are inspecting before diagnosing the B1978 code.

Need help with a B1978 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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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