[mustang67408]

Conditions for the EVAP MONITOR to run:
To complete the ”Internal Pressure Readiness” monitor, you must perform a ”Cold Soak” procedure prior to
conducting the driving pattern procedure.
Cold Soak Preconditions
The monitor will not run unless:

MIL is OFF

Fuel level is approximately 1/2 to 3/4

Altitude is 7,870 feet (2,400 m) or less
Cold Soak Procedure
(a) Start the engine and allow coolant temperature to reach 176°F (80°C) or higher
(b) Let vehicle cold cold soak for 8 hours or until the difference between IAT and ECT is less than 13°F
(7°C)
Before starting the engine, the difference between ECT and IAT must be less than 13°F (7°C)
Examples:
Scenario 1
ECT = 75°F (24°C)
IAT = 60°F (16°C)
Difference between ECT and IAT is 15°F (8°C)
" The monitor will not run because difference between ECT and IAT is greater than 13°F (7°C)
Scenario 2
ECT = 70°F (21°C)
IAT = 68°F (20°C)
Difference between ECT and IAT is 2°F (1°C)
" The monitor will run because difference between ECT and IAT is less than 13°F (7°C)
* NOTE for 2002 and later MY vehicles:
The readiness test can be completed in cold ambient conditions (less than 40°F/4.4°C) and/or at high
altitudes (more than 7,870 feet/2,400 m) if the drive pattern is repeated a second time after cycling
the ignition off.
Drive Pattern
(a) Connect the OBD II scan tool to the DLC3 to check monitor status and preconditions.
(b) Release pressure in fuel tank by removing and then reinstalling the fuel tank cap.
(c) Start the engine and allow to idle until ECT is 167°F (75°C) or higher.
(d) Run the engine at 3,000 rpm for about 10 seconds.
(e) Allow engine to idle with the A/C ON (to create a slight load) for 15 – 50 minutes.
NOTICE: If vehicle is not equipped with A/C

Securely set the parking brake.

Block the drive wheels with wheel chocks.

Allow vehicle to idle in drive for 15 – 50 minutes.

The way you described it, it was the gas cap.