Maint code
Did you get the maint fault code from the FMC? If so what was it.
Did you only get the lights come on after landing, you do not say when they came on.
For your info:
The Fuel Filter Bypass Light can only come on under the following conditions:
1. The fuel filter is about to be bypassed.
2. The EEC senses that the fuel filter signals disagree
3. The differential pressure swith has failed
4. The wires and connectors between the differential pressure switch and the DEU's failed.
The causes of these failures can be one of the following:
1. Filter contamination either fuel tank contamination, fuel pump contamination or HMU contamination.
2. Failure of the fuel filter differential swith.
3. A wire harness between the differential pressure switch and the EEC
4. The EEC
5. A DEU
6. The wiring (As in all things when you have isolated everything else) between the light and the DEU.
It would appear that as they changed the filters etc it was probably one of the first items.
I hope that helps - Or maybe not