Q: Ignition coil and Check Engine Light issue - 2008 Mercury Mariner

Hello, thanks for writing in! There is no such thing as a B location for a coil. You have six coils, that is one per cylinder you have. Without knowing where the bad coil was relocated to it would be hard to know. It will be one of the front three coils since the back three requires the intake manifold to be removed for access to the coils.

The Check Engine Light code P0351 relates to the PCM computer primary injector driver problem and burns out the coil driver for that coil.

The repair may require the replacement of all six coils and the engine control module (PCM). This problem is internal circuits of the PCM get burned out from the excessive coil resistance.

Once these components are replaced the PCM will need to be programmed to work with your key through the anti-thief module. The programming will need to be done by a Ford or Lincoln Mercury dealer.

To avoid any unnecessary repairs, I would highly suggest having a certified technician, such as one from YourMechanic, come diagnose your Check Engine Light firsthand and service your ignition coils as necessary.