Ford F150 Pickup. Instruction - part 1556

Fig. 320: Identifying Vapor Management Valve & Hose Ports 
Courtesy of FORD MOTOR CO. 

21) Check EVAP System For Stuck Open Valve 
Turn ignition switch to OFF position. Disconnect hoses from EVAP canister purge valve or Vapor 
Management Valve (VMV). Connect a vacuum pump to "Fuel Vapor To EVAP Canister" port on carbon 
canister and apply 16 in. Hg to port. See Fig. 319 or Fig. 320 . If vacuum bleeds off within 20 seconds, 
replace EVAP canister purge valve or VMV. If vacuum holds, reconnect hoses and go to next step. 

 

2003 Ford Pickup F150 

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

  

22) Check IAC Valve For Proper Function 
 
Start engine and allow to idle. Ensure transmission is in Park or Neutral and engine has reached normal 
operating temperature. Disconnect IAC valve harness connector. If engine speed drops or engine stalls, 
go to next step. If engine speed does not drop or engine does not stall, check throttle body for damage. 
Repair or replace as necessary. If throttle body is okay, replace IAC valve and perform 

PCM RESET 

PROCEDURE

 under CLEARING CODES under SELF-DIAGNOSTIC SYSTEM. 

23) Check IAC Circuit For Short To GND In Harness 
 
Turn ignition switch to OFF position. Disconnect scan tool from Data Link Connector (DLC). Disconnect 
PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. 
Using a DVOM, measure resistance between negative battery terminal and IAC circuit at PCM harness 
connector. See PCM CONNECTOR IDENTIFICATION and Fig. 318. If resistance is more than 10 
k/ohms, replace PCM (for high idle speed symptom), or reconnect all connectors and components and go 
to step 30) (all others). If resistance is 10 k/ohms or less, repair short to GND in IAC circuit. 

30) Check IAC System For Intermittent Open Or Short 
 
Connect scan tool to Data Link Connector (DLC). Start engine and allow to idle. Ensure all accessories 
are off and engine is warmed to normal operating temperature. Using scan tool, access IAC and RPM 
PIDs from PID/DATA MONITOR & RECORD menu. IAC duty cycle should be 20-45 percent. Observe 
IAC and RPM PIDs for indication of fault while performing the following: 

z

Shake, wiggle and bend wiring harness starting at IAC valve and work toward PCM.  

z

Lightly tap on IAC valve and wiggle connector to simulate road shock.  

Fault will be indicated by sudden change in IAC or RPM PID value. If any faults are found, isolate fault 
and repair as necessary. If no faults are found and an idle quality, starting or stalling symptom is currently 
present, replace IAC valve. If no faults are found, and idle is okay and a starting or stalling symptom is 
not currently present, check for intermittent faults. Go to TEST Z, step 1). 

TEST KF: FAN CONTROL RELAY 

Diagnostic Aids 

This system test is for Aviator, Escape, Focus, Ranger 2.3L, Sable, Taurus and Windstar only. On all models, 
PCM determines engine cooling fan requirements and controls fan operation through Low Fan Control (LFC), 
Medium Fan Control (MFC), and High Fan Control (HFC) circuits.

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 23) to step 30). No test procedures have been omitted.

NOTE:

After each service or repair procedure has been completed, reconnect all 
components. Clear DTCs and repeat QUICK TEST procedures to ensure all EEC-
V systems are working properly and DTCs are no longer present.

 

2003 Ford Pickup F150 

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

  

While performing these tests, use the wiring diagrams included in TEST KF. Wiring diagrams in SYSTEM 
WIRING DIAGRAMS article may use different terminology. 

Perform this test only when instructed by QUICK TEST or directed by other test procedures. This test is only 
intended to diagnose:  

z

Wiring Harness Circuits (B+, FAN PWR & VPWR, IGN START/RUN, LFC, MFC & HFC). See Fig. 
321-Fig. 330  

z

Low Speed Fan Control (LFC), Medium Speed Fan Control (MFC) & High Speed Fan Control (HFC) 
Relays  

z

Powertrain Control Module (PCM)  

Fig. 321: Identifying Cooling Fan Circuits (Aviator) 
Courtesy of FORD MOTOR CO. 

 

2003 Ford Pickup F150 

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

  

Fig. 322: Identifying Cooling Fan Circuits (Escape 2.0L) 
Courtesy of FORD MOTOR CO. 

 

2003 Ford Pickup F150 

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