Ford F150 Pickup. Instruction - part 1555

2) For KOER Only DTC P0505, For KOER & Continuous Memory DTCs P0506, P0507 & P1507, 
For KOEO, KOER & Continuous Memory DTC P1504: Or Starts Only At Part Throttle; Check 
VPWR Voltage To IAC Valve 
KOER DTC P0505 is set when PCM attempts to control engine idle speed and desired RPM could not be 
reached or controlled during self-test. KOEO, KOER and Continuous Memory DTC P1504 is set when 
PCM detects an electrical load failure on IAC output circuit. KOER and Continuous Memory DTC P1507 
is set when PCM detects engine idle speed is less than desired RPM. Possible causes are: 

z

IAC Circuit Open, Or Shorted To GND Or VPWR  

z

VPWR Circuit To IAC Valve Open  

z

Air Inlet Plugged  

z

Faulty IAC Valve  

z

Faulty PCM  

Turn ignition switch to OFF position. Disconnect IAC valve connector. Turn ignition switch to ON 
position. Using a DVOM, measure voltage between chassis ground and VPWR circuit at IAC valve 
harness connector. See Fig. 318. 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. 

3) Check IAC Valve Resistance 
 
Turn ignition switch to OFF position. Using a DVOM, measure resistance between both IAC valve 
terminals. If resistance is 6-13 ohms, go to next step. If resistance is not 6-13 ohms, replace IAC valve. 

4) Check IAC Valve For Internal Short To IAC Case 
 
Ensure ignition switch is turned to OFF position. Using a DVOM, measure resistance between IAC valve 
case and each IAC valve terminal. If both resistance measurements are more than 10 k/ohms, go to step 7)
(DTC P1504), or go to next step (all others). If either resistance measurement is 10 k/ohms or less, 
replace IAC valve. 

5) Check Air Inlet For Plugging 
 
Turn ignition switch to OFF position. Remove air filter. Inspect air filter, Mass Airflow (MAF) sensor 
and air inlet system for debris, blockage, excessive dirt or contamination. Repair as necessary. If air inlet 
system is okay, reinstall inlet air system and go to next step. 

6) Check For Inlet Air Leaks 
 
Start engine and allow to idle. Listen for vacuum leaks. Inspect air inlet system from MAF sensor to 
intake manifold for any of the following possible faults: 

z

Cracked Or Punctured Air Inlet Tube  

z

Loose Inlet Air Tube, IAC Tubes Or Air Cleaner Housing  

z

Loose Or Damaged Throttle Body 

prior to continuing with this test.

 

2003 Ford Pickup F150 

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

  

z

Contaminated Or Damaged IAC Valve, Or Gasket  

z

Faulty EGR Valve Or Gasket  

z

Damaged Vacuum Supply Connector Or Hose(s)  

z

Faulty PCV Valve, Connector Or Hose  

Check entire intake air system for vacuum leaks. Repair as necessary. If no vacuum leaks are found, go to 
next step. 

7) Check IAC Circuit For Open In Harness 
 
Turn ignition switch to OFF position. Disconnect IAC valve connector. Disconnect PCM connector(s). 
Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, 
measure resistance of IAC circuit between PCM harness connector and IAC valve harness connector. See 
PCM CONNECTOR IDENTIFICATION and Fig. 318. If resistance is 5 ohms or more, repair open in 
IAC circuit. If resistance is less than 5 ohms, go to next step. 

8) Check IAC Circuit For Short To PWR In Harness 
 
Turn ignition switch to ON position. Using a DVOM, measure voltage between negative battery terminal 
and IAC circuit at PCM harness connector. If voltage is one volt or more, repair short to PWR in IAC 
circuit. If voltage is less than one volt, go to next step. 

9) Check IAC Circuit For Short To Ground In Harness 
 
Turn ignition switch to OFF position. Disconnect scan tool from DLC. Using a DVOM, measure 
resistance between IAC and PWR GND circuits at PCM harness connector. See PCM PWR GND, SIG 
RTN & VREF TERMINAL IDENTIFICATION table. See PCM CONNECTOR 
IDENTIFICATION and 

Fig. 318

. If resistance is more than 10 k/ohms, replace PCM (DTC P0511, 

P1504), or go to next step (all others). If resistance is 10 k/ohms or less, repair short to ground in IAC 
circuit. 

10) Check IAC Signal From PCM 
 
Reconnect PCM and IAC valve harness connectors. Start engine and allow to idle. If engine stalls, place a 
shim under hard stop screw to maintain idle conditions. Using scan tool, access IAC and RPM PIDs from 
PID/DATA MONITOR & RECORD menu. Ensure engine is at normal operating temperature. With all 
accessories off and throttle closed, IAC duty cycle should be about 22-45 percent. Observe IAC PID 
value and slowly increase engine speed to 3000 RPM, then allow to return to closed throttle position (if 
closed throttle RPM is significantly higher than normal, ignore this part of the procedure). IAC duty cycle 
should increase as engine speed increases. If IAC PID value is not within specification at closed throttle 
or duty cycle does not respond to RPM change, replace IAC valve. If IAC PID value is within 
specification at closed throttle and duty cycle does respond to RPM change, go to step 30) (DTC P1504 
or P1507), or check throttle body for damage (all others). Repair as necessary. If throttle body is okay, 
replace IAC valve and perform PCM RESET PROCEDURE under CLEARING CODES under SELF-
DIAGNOSTIC SYSTEM. 

 

2003 Ford Pickup F150 

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

  

20) For Continuous Memory Only DTC P1506: Check For Vacuum Leaks 
DTC P1506 is set when PCM detects engine idle speed is more than desired RPM. Possible causes are: 

z

IAC Circuit Short To GND  

z

Damaged IAC Valve  

z

IAC Valve Stuck Open  

z

Vacuum Leaks  

z

Faulty EVAP System  

z

Damaged Powertrain Control Module (PCM)  

Start engine and allow to idle. Listen for vacuum leaks. Inspect air inlet system from Mass Airflow 
(MAF) sensor to intake manifold for any of the following possible faults:  

z

Cracked Or Punctured Air Inlet Tube  

z

Loose Inlet Air Tube, IAC Tubes Or Air Cleaner Housing  

z

Loose Or Damaged Throttle Body  

z

Contaminated Or Damaged IAC Valve, Or Gasket  

z

Faulty EGR Valve Or Gasket  

z

Damaged Vacuum Supply Connector Or Hose(s)  

z

Faulty PCV Valve, Connector Or Hose  

Check entire intake air system for vacuum leaks. Repair as necessary. If no vacuum leaks are found, go to 
next step. 

NOTE:

A break in step numbering sequence occurs at this point. Procedure skips 
from step 10) to step 20). No test procedures have been omitted.

NOTE:

For additional testing information, see DIAGNOSTIC AIDS.

NOTE:

EVAP canister is also referred to as carbon canister.

 

2003 Ford Pickup F150 

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

  

Fig. 319: Identifying EVAP Canister Purge Valve & Hose Ports 
Courtesy of FORD MOTOR CO. 

 

2003 Ford Pickup F150 

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