Turn ignition switch to ON position. Using scan tool, access CHT V PID from PID/DATA MONITOR &
RECORD menu. If CHT V PID voltage is more than 4.6 volts, replace CHT sensor. For LS and
Thunderbird, if CHT V PID voltage is 4.6 volts or less, go to step 22). For all others, go to next step.
21) Check VREF Circuit Voltage At TP Sensor
Disconnect TP sensor connector. Turn ignition switch to ON position. Using a DVOM, measure voltage
between VREF and SIG RTN circuits at TP sensor harness connector. See Fig. 163-Fig. 166 . If voltage
is 4-6 volts, VREF voltage is okay. Reconnect TP sensor and go to next step. If voltage is not 4-6 volts,
go to TEST C, step 1).
22) Check CHT Signal Circuit For Short To Ground
Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector for loose,
damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance between CHT
circuit, and PWR GND and SIG RTN circuits at PCM harness connector. See PCM PWR GND, SIG
RTN & VREF TERMINAL IDENTIFICATION table. See PCM CONNECTOR
IDENTIFICATION and Fig. 193 or Fig. 194 . If all resistance measurements are more than 10 k/ohms,
replace PCM. If any resistance measurement is 10 k/ohms or less, repair short between circuits.
30) For KOEO, KOER & Continuous Memory DTC P1285: Early Warning Of Engine Overheat
Condition
This DTC indicates that PCM sensed an engine overheat condition from CHT sensor. Possible causes for
fault are:
z
Low Engine Coolant Level
z
Engine Mechanical Concern
z
Engine Cooling System Concerns
z
CHT Sensor Concern
Check cooling system for external or internal leaks and restrictions. Check coolant level and cooling fan
operation. Check for blockage in radiator. Repair as necessary. If electric cooling fan does not operate,
see appropriate symptom under SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-
FUEL & GASOLINE article. If a cooling fan DTC is retrieved, see DIAGNOSTIC TROUBLE CODE
DEFINITIONS. If cooling system is okay and no faults are found, check CHT sensor operation. Go to
step 3).
NOTE:
A break in step numbering sequence occurs at this point. Procedure skips
from step 22) to step 30). No test procedures have been omitted.
NOTE:
For additional testing information, see DIAGNOSTIC AIDS.
NOTE:
A break in step numbering sequence occurs at this point. Procedure skips
from step 30) to step 40). No test procedures have been omitted.
NOTE:
Diagnostic procedures beginning with step 40) are performed when
2003 Ford Pickup F150
2003 ENGINE PERFORMANCE Self-Diagnostics - CNG, Flex-Fuel & Gasoline