The 2002 7.3-liter diesel is an 8-cylinder engine designed and manufactured by Ford Motor Company and is part of the Powerstroke line. The engine uses glow plugs to warm the cylinders to provide a smooth and efficient start. The glow plug control module, also called the relay, sends the signal to the glow plugs to begin the warming process. When the control module is faulty, the glow plugs never receive the signal and as a result do not warm the engine. If you notice the that your engine is hard to start or misfires, test the glow plug control module.
Park the vehicle in an area away from traffic and open the hood. Allow ample time for the engine to cool.
Locate the glow plug control module, which is positioned behind the fuel filter on the passenger side of the engine. The module is a large post with two wires connected to it. Refer to the vehicle repair manual for a diagram of this device.
Use a multimeter to test the control module. Select the "DC volts" function on the device on and set the test range to "15 volts."
Attach the positive lead wire to the control module post. Attach the negative lead wire to the negative battery terminal, which will act as a ground point. For reference, the positive lead is usually white and the negative lead is usually black.
Insert the key into the ignition and turn it one click, which should be the "On" position. Do not turn the key so far as to start the engine. This allows the powertrain control module (PCM) to start, which transmits a signal to the glow plug control module to begin the warming process.
Watch the multimeter dial or digital readout. The voltage should read between 10 and 15 volts. If the multimeter detects no activity or registers below 10 volts, then the glow plug control module is faulty and should be replaced.
