How Do I Check to See If My Ignition Module Is Bad on My 1997 Malibu?

The 1997 Chevy Malibu is available with two different engine sizes; the 2.4 liter 4-cylinder, better known as the quad four, and the 3.1 liter V-6. The ignition control module (ICM) on both engines varies in shape and location; however, they both work on the same principles. These procedures concentrate on the most predominant symptom of an ICM failure -- the no start. The procedures encompass all models. Intermittent no-start conditions, as in an impending failure, must be tested at the time of the failure.

Instructions

Understand the theory of operation and relationship of the components comprising the ignition system. The ICM supplies the power to the crankshaft sensor, cam sensor and the ignition coils when the key is on. When the engine is cranking the crankshaft sensor, which is a hall effect sensor, it acts as an on and off switch, sends a fluctuating AC voltage signal as to the ICM. This signal denotes the position of the crankshaft relative to the compression stroke on the number 1 cylinder.

Having received the crankshaft sensor signals, the ICM begins to toggle the ground on the coils causing the spark plugs to fire in the proper sequence. The timing of the spark plug firing is in a state of retarded timing to promote easier starting. As the fuel ignites and the engine speed exceeds 400 rpm, the ICM relinquishes timing control of the coil firing by sending a converted digital signal to the fuel injection computer.

The computer upon receiving informative signals from its various sensors, formulates a strategy for fuel injector opening times and engine spark timing. It sends a digital signal back to the ICM to regulate the coil firing.

Check the battery for a full charge. Without a full charge, the ICM will not operate normally. Place the voltmeter red lead on the positive battery terminal and the black lead on the negative terminal. There must be 12 to 12.75 volts. If not, charge the battery before proceeding.

Study the configuration of the electrical plug on the ICM. The ignition control module on this engine is flat and has three coils mounted above the module. It is located on the valve cover. The module has a single plug with two wires on one side and two plugs on the opposite side, one small with two wires and one large with 5 or 6 wires. For testing purposes, the only ones to be concerned with are the two small plugs on either side.

Notice that all the plugs have letters embossed on them designating the circuit. The single plug side of the module has a pink or pink with a black stripe wire on terminal A which is the switched power input wire. The second terminal with the letter B is a black wire with a white stripe. This wire is the ICM ground wire.

The small plug on the opposite side with the large plug below it is marked A, B and C. The A terminal is a yellow wire and the C terminal is a purple wire, both of which are for the crankshaft sensor. The middle B terminal is vacant.

The larger plug is not used in this testing procedure. The letters range from A to F. The A terminal with a tan with a black stripe and the B terminal white wire are both reference signals to and from the computer. The C terminal is for a tachometer is so equipped. The D terminal is vacant. The E terminal with a purple and white stripe wire is for fuel control. The F terminal with the red and black wire is the ground for the computer.

Check the coils for spark. This is to confirm a problem in the ignition. Pull a spark plug wire off a coil and install the spark plug wire tester on the coil tower and the other end in the spark plug wire end. Have the helper crank the engine. The tool will flash every ignition cycle if it the coil is firing. If the coil is firing the problem is elsewhere, such as the fuel circuit or internal problems. If not proceed to the next step after removing the tool and reinstalling the wire.

Check to make sure there is power to the ICM. It must have power and a good ground to work. Thread the wire piercing probe on the red voltmeter lead. If it wont thread on then connect the alligator clip to the red probe end. Place the piercing probe on the A terminal with the pink or pink wire with a black stripe on the side of the ICM with one plug. Try to keep the probing downstream at least three inches from the connector to prevent any accidental pulling on the terminals. Place the black voltmeter lead on the battery negative terminal. Turn the key on. There must be 12 to 12.75 volts. If not the problem is in the wiring not the ICM. Turn the key off.

Check to see if the ICM has a good ground circuit. For this use the same plug but probe the B terminal with the black wire with the white stripe using the black voltmeter lead probe. Place the red lead on the positive terminal on the battery. Turn the key on. Once again, battery voltage of 12 too 12.75 volts must be present. If not the ground is defective and must be traced and repaired. If the voltage was correct, proceed.

Check to see if the crankshaft position sensor is indeed operating and sending an AC voltage signal to the ICM. This test will involve probing both wires on the opposite side of the module with two plugs. Place both probes on wires on the small plug with the A terminal yellow wire and the C terminal with the purple wire. Polarity isn't an issue so either way is acceptable. Turn the voltmeter to AC volts.

Crank the engine. The AC voltage should fluctuate between .3 volts and 1.0 volts AC rapidly. The voltage may vary a small amount due to the amperage in the battery, viscosity of the oil and so on. The exact voltage at this point is not as important as the fact that the sensor is sending a fluctuating AC voltage. Turn the key off. If no voltage is present the crankshaft sensor is not working. Look at the wiring from the crankshaft sensor located in the block above the oil pan and under the exhaust manifold. This engine has a problem with the sensor wires burning or shorting out against the block due to their location and the heat. If the wiring is good replace the sensor. If the voltage was correct, preform the next tests before condemning the ICM.

Test the resistance of the crankshaft sensor. It is possible that although the sensor displayed the right AC voltage with the engine cranking, it may not have a strong enough signal to operate the ICM. Leave the probes in place. Turn the voltmeter to the ohms scale. There must be between 300 too 500 ohms. If the resistance is incorrect replace the sensor. If it is correct replace the ICM.

The ICM on a 1997 Malibu with a 2.4 liter engine is separate from the coils. This is an excellent engine with good power to a good power to weight ratio. The engine is very dependable and has decent fuel economy. It is however, kind of unique in that it has the spark plugs centered in the cylinder head.

There is a metal cover bolted to the cylinder head. Bolted to the bottom of the cover is a plastic distributor housing with extensions molded into the housing that are designed to fit in the spark plug holes to deliver the power to the spark plugs. Between the housing and the metal cover there are two coils. The coils transfer their power to a copper inlay to each spark plug extension. The ICM is mounted below and to the rear transmission side of the top cover. As a note, these engines are notorious for having a failure of the distributor housing due to the copper inlay burning through. When this happens a miss in the engine occurs.

Study the wiring layout of the electrical plug protruding out from under the metal engine cover on the transmission side. The plug will have 6 wires across the top and two on the bottom. Each of the terminals will have a letter embossed on it to identify the circuit. The letters range from A to L of which three terminals are vacant. Starting with the bottom two wires, the terminal marked with an A with a white wire is the 1 and 4 coil control signal from the computer. The B terminal has an orange wire and is the 2 and 3 control signal from the computer. The F terminal with the yellow wire is the crankshaft sensor signal. The G terminal with the purple and white wire is the digital crankshaft 7X signal from the ICM to the computer. The H terminal with the red and black wire is the ground for the computer. The J terminal with the purple wire is a crankshaft sensor circuit. The K terminal with a black wire is the ground for the ICM. The last terminal is the L terminal with a pink wire. This is the switched power to the ICM.

Test the L terminal with a pink wire. Place the red voltmeter lead with the wire piercing probe on the pink wire. Place the black lead on the battery negative terminal. Turn the key on. There must be 12 to 12.75 volts. If the voltage is out of range or no voltage the wire must be traced and repaired before retesting. Turn the key off.

Test the ground circuit for the ICM. Hook the voltmeter black lead with a probe to the K terminal black wire. Place the red lead on the positive terminal on the battery. Turn the key on. Battery voltage must once again be present at 12 to 12.75 volts. If the voltage is less then the ground circuit is compromised. Trace the wire and restore a good ground to the ICM. Turn the key off.

Test the crankshaft sensor for a good signal. This involves probing the F yellow and J purple wires simultaneously. This can be done in any order since polarity is no issue. Place the voltmeter on AC volts. Turn the key on. It must display 0 volts. Have the helper crank the engine. The AC voltage must fluctuate rapidly between .3 and 1.3 volts. The voltage may differ slightly depending on the engine rpm while cranking. The most important observation is the generation of a voltage and that it fluctuates. This means the sensor is working. Turn the key off. If there was no voltage the sensor is bad. If the voltage was good, the sensor is most likely good, however, it may be working but have insufficient signal for the ICM. Continue to the next test.

Test the G terminal with the purple wire with a white stripe. This is the 7X crankshaft signal that the ICM recieved in a AC voltage format and has now converted to a digital signal to the computer. This test will examine how clean the frequency wave is to the computer. Connect the red voltmeter lead with the probe on the G terminal purple and white wire and the black lead to the battery negative terminal. Place the voltmeter on Hertz. Turn the key on. The display must be 0 indicating the meter is working. Have a helper crank the engine. The display must show a fluctuating Hertz in the 29 to 39 range with no major spikes in Hertz. Turn the key off. If the frequency of the Hertz was in the correct range the ICM is fine and producing a clean digital signal. If the Hertz value was not correct or none was present the ICM is defective and must be replaced.

Test the signal from the computer used to fire the coils. The A terminal with the white wire and the B terminal with the orange wire are used for this test. In this test only one wire will be tested at a time however both wires must have the same result. Place the red voltmeter lead with a probe on the A terminal white wire and the black voltmeter lead on the negative battery terminal. Have a helper turn the key on. It must show 0 Hertz. Crank the engine. The display must fluctuate around 5 Hertz. Move the probe to the B terminal with the orange wire and repeat the test. Turn the key off. If the Hertz values were within range the ICM is defective. If the values were not within range the problem is not with the ICM. It is elsewhere.