Hi all just put reader on my sons car and it is showing "Fuel trim bank A "  Could someone explain please,the car is running fine. Thanks in advance

It's usually indicative of a tired pre-cat lambda probe leading to either a slightly rich or slightly lean fuel trim depending which way the probe has gone, this error is being flagged up by the post-cat lambda probe as either too much or too little oxygen in the exhaust gases.

You can cure it temporarily by simply clearing the code which sets the fuel trim back to default mapping.

Thanks ever so much,really appreciated.