Obd codes

p38 1997 4.0

i have plugged in obd reader and am getting fault code P3999 which is manufacturer specific,has anyone any idea of fault code meaning please...

Was getting this one for a while on my 96 4.0 along with AMFR MAF Codes, sorted out the MAF and it disappeared.
Also had it along with oxy sensor fault code ages ago, came up twice on my reader.

Not sure if its just a ghost code or something to do with LR but it just seemed to acompany faults?

many thanks for your help boys,it seems as though it is just a ghost code then and nothing to worry about