Superduty

P0148 is "High pressure common rail Checksum" error.

Page 9-1116 in the 05 shop manual.

A deviation between the rail pressure and the desired pressure, ie what the ECM wants.

Can you scan the rail pressure with your tool ?

Things to check for LOW rail pressure according to the 05 shop manual.

1) Rail pressure sensor. Check rail pressure at idle. Rev the engine up to 2000 RPM. Check the rail pressure again. It should be higher. You could check this with a voltmeter too.

2) Lift pump flow

3) Rail pressure limiting valve
- dealer has to perform a test with the scan tool for this. Or you could disconnect the return line from it and see if you have flow from it.

4) Leaking fuel injectors

5) CP3

03 ant a hemi

The book for 04 says the fuel lift pump is still direct ECM controlled.The 05 switched to a external relay. My diagrams may be wrong. Or an update may have come out.

03 ant a hemi

The rail pressure limiting valve will only open if excesive pressure is built up in the rail. (Mechaniclly operated) It will operate very little.
The rail pressures can be measured with a volt meter from the fuel rail pressure sensor. I cant find the values right now though.
A little info... Once the rail pressure gets high the pressure sensor shuts off the FCA (fuel control actuator), this cuts flow of fuel into the high pressure side of the CP3, now the CP3 wont produce rail pressure. The fuel bypasses inside the CP3 as the injectors releive pressure through operation, the rail pressure sensor sends a signal to the FCA which will open again and allow fuel back into the CP3 high pressure side. once again building rail pressure. I will try to find the values tomorrow after work.