Ford F150 Pickup. Instruction - part 1564

Ensure ignition switch is turned to OFF position. Using a DVOM, measure resistance between chassis 
ground and GND circuit at driver's side cooling fan harness connector. If resistance is less than 5 ohms, 
replace driver's side cooling fan. Recheck cooling fans operation. If resistance is 5 ohms or more, repair 
open in GND circuit. Recheck cooling fans operation. 

108) Measure Resistance Of HIGH FAN PWR Circuit 
 
Ensure ignition switch is turned to OFF position. Using a DVOM, measure resistance of HIGH FAN 
PWR circuit between driver's side cooling fan and HFC relay No. 1 (MAIN FAN) cavity. If resistance is 
less than 5 ohms, replace HFC relay No. 1 (MAIN FAN). Recheck cooling fan operation. If resistance is 
5 ohms or more, repair open in HIGH FAN PWR circuit. Recheck cooling fan operation. 

110) Check B+ To LFC Relay 
 
Turn ignition switch to OFF position. Remove LFC relay (ADD FAN). See COOLING FAN RELAY 
LOCATIONS table. Using a DVOM, measure voltage between negative battery cable and B+ circuit at 
LFC relay cavity. See Fig. 323 or Fig. 324 . If voltage is more than 10.5 volts, go to next step. If voltage 
is 10.5 volts or less, check for open in B+ circuit. Check appropriate B+ circuit fuse. If fuse is okay, 
check for open in B+ circuit. Repair as necessary. If fuse is blown, check B+ and FAN PWR circuits for 
short to ground before replacing fuse. Repair as necessary. Recheck cooling fan operation. 

111) Command Low Speed Fan ON & Check For B+ To Passenger's Side Cooling Fan 
 
Turn ignition switch to OFF position. Reinstall LFC relay. Disconnect passenger's side cooling fan. Turn 
ignition switch to ON position. Using scan tool, access OUTPUT TEST MODE. Command low speed fan 
ON. Using a DVOM, measure voltage between chassis ground and passenger's side cooling fan harness 
connector LOW FAN PWR circuit terminal. If voltage is more than 10.5 volts turn ignition switch to OFF 
position and go to next step. If voltage is 10.5 volts or less, turn ignition switch to OFF position and go to 
step 113). 

112) Measure Resistance Of LOW FAN GND Circuit 
 
Ensure ignition switch is turned to OFF position. Remove HFC relay No. 2 (ADD FAN 2). Using a 
DVOM, measure resistance of LOW FAN GND circuit between HFC relay cavity and passenger's side 
cooling fan harness connector. If resistance is less than 5 ohms, replace passenger's side cooling fan. 
Recheck cooling fan operation. If resistance is 5 ohms or more, repair open in LOW FAN GND circuit 
between passenger's side cooling fan and HFC relay No. 2 (ADD FAN 2). Recheck cooling fan operation. 

113) Measure Resistance Of LOW FAN PWR Circuit 
 
Ensure ignition switch is turned to OFF position. Remove LFC relay. See COOLING FAN RELAY 
LOCATIONS table. Using a DVOM, measure resistance of LOW FAN PWR circuit between 
passenger's side cooling fan and LFC relay cavity. If resistance is less than 5 ohms, replace LFC relay. 
Recheck cooling fan operation. If resistance is 5 ohms or more, repair open in LOW FAN PWR circuit. 

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 108) to step 110). No test procedures have been omitted.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline

  

Recheck cooling fan operation. 

115) Check Cooling Fans For Proper Operation 
 
If driver's side cooling fan did not operate in step 85), go to next step. If passenger's side cooling fan did 
not operate in step 85), go to step 118). 

116) Check B+ & IGN START/RUN Circuits To HFC Relay No. 1 (MAIN FAN) 
 
Turn ignition switch to OFF position. Remove HFC relay No. 1 (MAIN FAN). See COOLING FAN 
RELAY LOCATIONS table. Using a DVOM, measure B+ circuit voltage between negative battery 
cable and HFC relay cavity. See Fig. 323 or Fig. 324 . Also, measure voltage between negative battery 
cable and IGN START/RUN circuit at HFC relay No. 1 (MAIN FAN) cavity. If both voltage 
measurements are more than 10.5 volts, turn ignition switch to OFF position and replace HFC relay No. 
1. If voltage is 10.5 volts or less, turn ignition switch to OFF position and check appropriate B+ or IGN 
START/RUN circuit fuse. If fuse(s) is okay, check for open in appropriate circuit. Repair as necessary. If 
fuse(s) is blown, check B+ and HIGH FAN PWR circuits for short to ground before replacing fuse(s). 
Repair as necessary. Recheck cooling fan operation. 

118) Check IGN START/RUN & GND Circuits To HFC Relay No. 2 (ADD FAN 2) 
 
Turn ignition switch to OFF position. Remove HFC relay No. 2 (ADD FAN 2). See COOLING FAN 
RELAY LOCATIONS table. Turn ignition switch to ON position. Using a DVOM, measure voltage 
between IGN START/RUN and GND circuits at HFC relay No. 2 (ADD FAN 2) cavities. See Fig. 323 or 
Fig. 324 . If voltage is more than 10.5 volts, turn ignition switch to OFF position and go to step 121). If 
voltage is 10.5 volts or less, go to next step. 

119) Check IGN START/RUN Voltage To HFC Relay No. 2 (ADD FAN 2) 
 
Using a DVOM, measure voltage between chassis ground and IGN START/RUN circuit at HFC relay 
cavity. If voltage is more than 10.5 volts, turn ignition switch to OFF position and repair open GND 
circuit to HFC relay No. 2 (ADD FAN 2). If voltage is 10.5 volts or less, turn ignition switch to OFF 
position and repair open in IGN START/RUN circuit to HFC relay No. 2 (ADD FAN 2). Recheck 
cooling fan operation. 

121) Check LOW FAN GND Circuit Between Passenger's Fan & HFC Relay No. 2 (ADD FAN 2) 
 

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 113) to step 115). No test procedures have been omitted.

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 116) to step 118). No test procedures have been omitted.

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 119) to step 121). No test procedures have been omitted.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline

  

Ensure ignition switch is turned to OFF position. Disconnect passenger's side cooling fan. Using a 
DVOM, measure resistance of LOW FAN GND circuit between HFC relay No. 2 (ADD FAN 2) cavity 
and passenger's side cooling fan harness connectors. See Fig. 323 or Fig. 324 . If resistance is less than 5 
ohms, go to next step. If resistance is 5 ohms or more, repair open in LOW FAN GND circuit between 
HFC relay No. 2 (ADD FAN 2) and splice to passenger's side cooling fan. Recheck cooling fan operation. 

122) Measure Resistance Of HFC Circuit Between HFC Relays No. 1 & 2 
 
Ensure ignition switch is turned to OFF position. Remove HFC relay No. 1 (MAIN FAN). See 
COOLING FAN RELAY LOCATIONS table. Using a DVOM, measure resistance of HFC circuit 
between HFC relays No. 1 and 2 cavities. See Fig. 323 or Fig. 324 . If resistance is less than 5 ohms, 
replace HFC relay No. 2 (ADD FAN 2). Recheck cooling fan operation. If resistance is 5 ohms or more, 
repair open in HFC circuit between HFC relays No. 1 (MAIN FAN) and No. 2 (ADD FAN 2). Recheck 
cooling fan operation. 

124) Check Operation Of Both Fans With HFC Relay No. 2 (ADD FAN 2) Disconnected & Low 
Fan Commanded ON 
 
Ensure ignition switch is turned to OFF position. Remove HFC relay No. 2 (ADD FAN 2). See 
COOLING FAN RELAY LOCATIONS table. Turn ignition switch to ON position. Using scan tool, 
access OUTPUT TEST MODE. Command low speed fan ON. If both fans now operate, replace HFC 
relay No. 2 (ADD FAN 2) for stuck closed contacts. Recheck cooling fan operation. If only one cooling 
fan operates, no fault is indicated, concern may be intermittent. Repeat step 85). If results are the same, 
return to SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-FUEL & GASOLINE 
article. 

132) Check Operation Of Cooling Fans 
Ensure ignition switch is in ON position. Using scan tool, access OUTPUT TEST MODE. See OUTPUT 
TEST MODE under ADDITIONAL SYSTEM FUNCTIONS. Command cooling fans on HIGH and 
LOW. If cooling fans operate, go to next step. If cooling fans do not operate, proceed as follows: 

z

If driver's and passenger's side cooling fans do not operate at any speed, go to step 134).  

z

If driver's and passenger's side cooling fans do not operate at LOW speed only, leave ignition 
switch in ON position and scan tool in OUTPUT TEST MODE. Go to step 138).  

z

If driver's side cooling fan does not operate at HIGH speed only, leave ignition switch in ON 
position and scan tool in OUTPUT TEST MODE. Go to step 138).  

z

If passenger's side cooling fan does not operate at HIGH speed only, leave ignition switch in ON 
position and scan tool in OUTPUT TEST MODE. Go to step 142).  

133) Check Operation Of Cooling Fans (Medium Speed) 

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 122) to step 124). No test procedures have been omitted.

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 124) to step 132). No test procedures have been omitted.

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline

  

 
Turn ignition switch to OFF position. Remove LFC (fan braking) relay and MFC (resistor) relay. See 
COOLING FAN RELAY LOCATIONS table. Turn ignition switch to ON position. Connect a fused 
jumper between LFC (fan braking) relay cavity No. 5 (Dark Blue wire) and MFC relay cavity No. 4 
(Red/Orange wire). If cooling fans do not operate, go to step 145). If cooling fans operate, system is okay. 
Go to appropriate symptom under SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, 
FLEX-FUEL & GASOLINE article. 

134) Check LFC (Fan Braking) Relay 
 
Turn ignition switch to OFF position. Remove LFC (fan braking) relay. See COOLING FAN RELAY 
LOCATIONS table. Using a DVOM, measure resistance between specified relay terminals. See MINI 
ISO RELAY RESISTANCE SPECIFICATIONS table. See 

Fig. 306

. If relay resistance is not as 

specified, replace LFC (fan braking) relay. If relay resistance is as specified, connect 2 jumper wires from 
positive battery terminal to relay terminals No. 30 and 85. Connect another jumper from relay terminal 
No. 86 to chassis ground. Using a DVOM, measure voltage between relay terminals No. 86 and 87. 
Disconnect jumper from relay terminal No. 85 and measure voltage between relay terminals No. 86 and 
87a. If battery voltage is present at both points, go to next step. If battery voltage is not present at one or 
both points, replace LFC (fan braking) relay. Recheck cooling fan operation. 

MINI ISO RELAY RESISTANCE SPECIFICATIONS 

135) Check Voltage To LFC (Fan Braking) Relay 
 
Turn ignition switch to ON position. Using a DVOM, measure voltage between chassis ground and fan 
braking relay cavity No. 87 (Dark Blue wire). If voltage is more than 10 volts, go to next step. If voltage 
is 10 volts or less, repair open or high resistance in B+ circuit to LFC (fan braking) relay. Recheck 
cooling fan operation. 

136) Check MFC (Resistor) Relay 
 
Turn ignition switch to OFF position. Remove MFC (resistor) relay. See COOLING FAN RELAY 
LOCATIONS table. Using a DVOM, measure resistance between specified relay terminals. See MINI 
ISO RELAY RESISTANCE SPECIFICATIONS table. See Fig. 306. If relay resistance is not as 
specified, replace MFC (resistor) relay. If relay resistance is as specified, connect 2 jumper wires from 
positive battery terminal to relay terminals No. 30 and 85. Connect another jumper from relay terminal 
No. 86 to chassis ground. Using a DVOM, measure voltage between relay terminals No. 86 and 87. 
Disconnect jumper from relay terminal No. 85 and measure voltage between relay terminals No. 86 and 
87a. If battery voltage is present at both points, go to next step. If battery voltage is not present at one or 

Measure Between Terminals No.

Ohms

85 & 86

50-100

30 & 87a

Less Than 5 Ohms

30 & 87

More Than 10 k/ohms

30 & 86

More Than 10 k/ohms

86 & 87a

More Than 10 k/ohms

86 & 87

More Than 10 k/ohms

 

2003 Ford Pickup F150 

2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline