Question

2004 Mitsubishi Diamante with engine code P0451 I already replaced the sensor on top of the fuel tank and the code came back.
I have a compact scanner (ElmScan 5), nice tool. Check engine light was on -code 451. Resaearch indicated code related to fuel tank/evap pressure. Sensor located on top of fuel pump unit with easy access via access plate on top of fuel pump so I replaced it. Light came back on within two weeks. Any other logical choices could be causing code?

BTW fuel guage is inoperative as well but was so for many month before any code set. Guage does move when appropriate wires are jumped so logically the defect is in the sending portion of the circuit. I don't believe this is related to code 451.

Answer 1

You need to test the wiring for the sensor,the fact that the sending unit isn't working can be sort of a hint to the wiring issue. However, the code means the voltage from the sensor is not changing when it should. A leak in the evap system could make this code appear. I suggest a smoke test to check for any leaks in the system, then take it from there.

Answer 2

P0451 Mitsubishi Code - EVAP System Pressure Sensor Range/Performance
Read more: https://www.autocodes.com/p0451_mitsubishi.html