Tuesday, February 28, 2012

How to inspect, test and replace engine control module?

A semi-conductor control for an electronic-ignition system.
See the image below :---

Inspect :--

Electronic and computer controlled ignitions use transistors as switches. These transistors are contained inside a control module housing that can be mounted on or in the distributor or remotely mounted on the vehicle's fire wall or another engine compartment surface.
Control modules should be tightly mounted to clean surfaces. A loose mounting can cause a heat build-up that can damage and destroy transistors and other electronic components contained in the module.
Some manufactures recommend the use of a special heat-conductive silicone grease between the control unit and its mounting. This helps conduct heat away from the module, reducing the chance of heat-related failure.
During the visual inspection, check all electrical connections to the module. They must be clean and tight. The wiring insulation should also be intact.
Look for evidence of burning. if there is, check the coil ground strap.
Not all damage can be seen, so test the control module to be sure that it is working properly.

TEST :--

Perform a no-start diagnosis of the ignition system.
Use an ohmmeter to ensure that the ignition module connection to ground is good. one lead of the meter should be connected to the ground terminal at the module and the other to a good ground. zero resistance indicates good continuity in the ground circuit. any resistance reading during this test is unacceptable.
The most effective method of testing for a defective ignition module is to use an ignition module tester, if one is available for that module.
Keep in mind that ignition modules are very reliable. They are also one of the most expensive ignition system components. So, if a module tester is not available, check out all other system components before condemning the ignition module.
The control module can be tested at any of our store locations.


The ignition module removal and replacement procedure varies depending on the ignition system. Always follow the procedure in the vehicle manufacture's service manual.

For a distributor-mounted module:

Remove the battery wire from the coil battery terminal, and remove the inner wiring connector on the primary coil terminals. Remove the spark plug wires from the cap.
Rotate the distributor latches one-half turn and lift the cap from the distributor.
Remove the two rotor retaining bolts and the rotor.
Remove the primary leads and the pickup leads from the module.
Remove the two module mounting screws, and remove the module from the distributor housing.
Wipe the module mounting surface clean, and place a light coating of silicone heat-dissipating grease on the module mounting surface.
Lack of silicone grease on the module mounting surface may cause module overheating and damage.
Install the module and tighten the module mounting screws to the specified torque.
Install the primary leads and pickup leads on the module.
Be sure the lug on the centrifugal advance mechanism fits into the rotor notch while installing the rotor, and tighten the rotor mounting screws to the specified torque.
Install the distributor cap, and be sure the projection in the cap fits in the housing notch.
Push down on the cap latches with a screwdriver, and rotate the latches until the lower part of the latch is hooked under the distributor housing.
Install the coil primary leads and battery wire on the coil terminals. Be sure the notch on the primary leads fits onto the cap projection. Install the spark plug wires.

This will help.

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