z
Open VPWR to LFP relay.
z
Faulty LFP relay.
z
Faulty PCM.
Turn ignition switch to OFF position. Remove low speed fuel pump relay from battery junction relay box
located in engine compartment. Turn ignition switch to ON position. Using a DVOM, measure voltage
between chassis ground and VPWR circuit at low speed fuel pump relay cavity. See Fig. 304. If voltage
is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open in VPWR circuit
between PCM power relay and low speed fuel pump relay.
46) Check Low Speed Fuel Pump Relay
Turn ignition switch to OFF position. Using a DVOM, measure resistance between LFP relay terminal
No. 85 and all other LFP relay terminals. See
Fig. 306
. Resistance between LFP relay terminals No. 85
and 86 should be 40-100 ohms. Resistance between LFP relay terminal No. 85 and all other terminals
should be more than 10 k/ohms. If any resistance measurement is not as specified, replace LFP relay. If
all resistance measurements are as specified, go to next step.
47) Check Low Fuel Pump Circuit For Short To PWR In Harness
Ensure ignition switch is turned to OFF position. Disconnect PCM connector. Inspect connector for loose,
damaged or corroded terminals. Repair as necessary. Turn ignition switch to ON position. Using a
DVOM, measure voltage of LFP circuit between chassis ground and LFP relay cavity. If voltage is less
than one volt, go to next step. If voltage is one volt or more, repair short to PWR in LFP circuit.
48) Check LFP Circuit For Short To Ground In Harness
Turn ignition switch to OFF position. Disconnect scan tool from Data Link Connector (DLC). Using a
DVOM, measure resistance between chassis ground and LFP circuit cavity at LFP relay. If resistance is
more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in LFP
circuit.
49) Check For Open LFP Circuit
Using a DVOM, measure resistance of LFP circuit between PCM harness connector and LFP relay
cavity. See PCM CONNECTOR IDENTIFICATION and Fig. 304. If resistance is less than 5 ohms,
replace PCM. If resistance is 5 ohms or more, repair open in LFP circuit.
55) Check For Open Fuel Pump Ground Circuit Through Resistor (F150 Lightning 5.4L SC)
Turn ignition switch to OFF position. Remove low speed fuel pump relay from battery junction relay box
located in engine compartment. Turn ignition switch to ON position. Using scan tool, access FPM PID
from PID/DATA MONITOR & RECORD menu. If FPM PID indicates OFF, no fault is indicated at this
NOTE:
A break in step numbering sequence occurs at this point. Procedure skips
from step 49) to step 55). No test procedures have been omitted.
2003 Ford Pickup F150
2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline