96-1 and 96-12 Have the exact same description below.
9-7 Is for Volvo care track and you will always have that code if you don't subscribe to it.
96 Fault mode
FMI 12
Detection conditions:The engine control unit (E-ECU) registers: that the rail pressure control is not working correctly
Symptom:
○ Yellow central warning
○ Max. speed is limited to 1100 rpm by the engine protection function
○ Torque reduction
Possible causes:
○ Damaged wire harness or connector
○ Defective fuel rail pressure sensor.
○ Leakage in high pressure fuel system, check the following components:
Fuel pressure relief valve (PRV)
Fuel rail pressure sensor
High pressure fuel pipes
Fuel injectors
Fuel nozzles
Fuel rail
○ Defective fuel control valve (FCV).
○ Defective high pressure fuel pump.
○ Defective camshaft lobe
○ Insufficient fuel supply
In my experience these systems are time consuming and difficult to narrow down hence why they probably threw parts it. Fuel rail pressure leaks are unlikely, would be obvious external or if leaking internally would have fuel in the oil. There was/is a common problem with an updated regulator(FCV) and rail pressure sensor that if memory serves me correctly Volvo now only sells them in a kit together, on the low side I have seen loose fuel supply pump belt or incorrectly installed water separator bowl, drain or sensor. On the high end the high pressure pump could be going bad or a injector or 3 with high return that could be determined with some testing.