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FICM Voltage Testing
Caution! The following test procedure will expose you to hazardous voltages that can injure or kill you. Use caution when testing your FICM. DO NOT allow your test probe to come in contact with the test screw and FICM housing at the same time, FICM damage will result!
For this test, you will need an accurate digital voltmeter. Perform this test when the engine is cold and the outside temperature is below 60 degrees. The FICM is mounted to the engine on the drivers side under the coolant overflow tank. Start by removing the two bolts that hold the coolant reservoir to the cowl and push the reservoir out of the way forward and to your right. You do not need to disconnect any of the hoses. On top of the FICM is a small cover held on by two #20 Torx screws; remove these two screws and pry the cover off. On 2003 and early 2004 trucks, you will see 7 screw heads under the cover (pic of 7 screw version). On 2004 and later trucks you will see 4 screw heads (pic of 4 screw version).
For the 4 screw version, take your voltmeter and set it on DC volts and connect the ground lead to battery negative, and with the key ON measure the voltage at the screw on your right—closest to the driver’s side fender. The voltage should be right at 48 volts. Anything between 47 and 49 is good. Have an assistant cycle the key and measure the voltage during the initial key-on buzz test. Voltage should not drop below 46 volts. Next measure the voltage while cranking the engine. If voltage stays at or above 45-46 volts, the FICM is fine. Abnormally low battery voltage can give a false low FICM voltage reading, so make sure your batteries are good. The procedure is the same for FICM’s with 7 screws, except that you will be checking voltage at a different screw. Put the positive lead on the left-most screw in the row of 4 screws. If the voltage is above 46 volts in all the tests, your FICM is in excellent condition. If it is between 36 and 45 volts its OK, but not great. If it is between 25 and 35 volts, you have serious FICM problems.