QuestionMy 99 blazer won't start.Replaced fuel filter, has new altenator, and waterpump.It is showing these codes: 0174 and 0171. It is getting power to fuel relay, but not to the fuel pump.Also don't know where to find the oil pressure switch, which I understand can cause truck to not get power to fuel pump.
any advise would be greatly appreciated.
thanks
daphne
AnswerHello Daphne,
Someone was on the right track, but not 100% correct.
The oil pressure switch, which is located near the rear of the intake manifold, supplies power to the fuel pump when oil pressure is above 4PSI.
This is a backup system to the relay.
In a normally operating engine, the relay is closed sending power as long as there is a crank signal, and the oil pressure switch is closed, also sending power to the pump. If either system quits, for whatever reason, the other will continue sending power, until that systems driving force is lost also.
Redundant system.
Now...power to the relay....There should always be power to one terminal of the relay. Usually it is an ORANGE wire. Then when the switch is turned to run, there should be power to a different terminal, dark green/white wire, which closes the relay, and sends power through a third terminal, gray wire, to the pump.
Power is also always available to the oil pressure switch, also an orange wire.
That switch also supplies power on a gray wire to the pump.
The gray wires are connected to each other.
The orange wires are also connected to each other, and powered by the same fuse or fusible link.
If you do not have power to the orange wires, check the instrument panel fuse block, fuse 9, probably marked ECM Batt.
Van
