How to Test an Ignition Control Moduleby Michelle Schaefer
The electronic ignition control module is a solid state "On/Off" switch for the ignition system. The module receives a signal from a sensor inside the distributor. The signal is then used to fire the ignition coil creating the energy for the spark plugs. The ignition module may be located inside the distributor, on the distributor housing, or mounted to the side of the engine compartment. When a module goes bad, it normally fails totally and the engine won't run at all. Checking your ignition module is an easy task that requires only the simplest of tools.
Remove one plug wire at the spark plug and insert an old spark plug into the end of the plug boot. Place the spark plug on a metal surface on the engine. Crank the engine and check for a spark at the old spark plug. No spark on the plug indicates an ignition problem.
Check for voltage at the coil positive terminal when the ignition key is on. Place the red lead of the multimeter on the positive coil terminal. Place the black lead to the battery negative terminal. Turn on the ignition switch to the "Run" position. The multimeter should read battery voltage at the positive terminal. If voltage is not present, then the problem is with the ignition switch or ignition wiring circuit.
Locate the ignition module positive (+) wire. Turn the key "Run" position without starting the engine. Pierce the positive wire with the multimeter's red lead. There should be a reading of battery voltage at the wire. If battery voltage is not present, check for an open circuit between the wire and the ignition switch.
Locate the ignition module negative (-) wire. Pierce the negative wire with the multimeter's red lead. Remove the distributor cap without removing the spark plug wires. Rotate the distributor center shaft by hand or by cranking the engine. Observe the distributor rotor as the engine is being cranked over. If the distributor rotor fails to turn, then the distributor or distributor gears are bad. The multimeter should read voltage alternating between battery voltage and zero.
Replace the ignition module if the multimeter reading fails to fluctuate between battery voltage and zero as the distributor is turning. Install the distributor cap and fasten it securely to the distributor. Disconnect the multimeter from the ignition module and battery.
- A fender cover or old blanket will protect the finish of your vehicle when working under the hood.
Items you will need
- Old spark plug
- Digital multimeter
- AutoZone Repair Guide:Testing The Ignition Module
- "Automotive Electrical Manual"; Haynes; 1990
- Jupiterimages/Comstock/Getty Images