Actually.. On OBD2 models, the Lift Pump is monitored, at least its voltage (amp) is..
Intermittent P0231 code
P0230- Fuel Pump Relay Control Circuit
P0231- Fuel Pump Secondary Circuit Low
P0232- Fuel Pump Secondary Circuit High
More info on
As I understand it.. The PCM notes the LP voltage (amperage draw) during Startup Mode, and uses that reading to monitor the LP performance for the duration of that ignition cycle.. Thats why alot of LP failures dont SET DTCS, during STARTUP MODE, its noting the skewed voltage reading of an already struggling and/or damaged liftpump..
The IP is the last of a long list of possible suspects.. Dont be so quick to convict without all the FACTS. Rush to judgement often compounds the pain and suffering of a costly misdiagnosis..