GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 Terraza Ext. 🢒 Engine 🢒 Engine Controls - 3.5L (LX9) 🢒 Electronic Ignition (EI) System Diagnosis

Circuit Description

There are 3 dual-tower ignition coils that are part of the ignition control module (ICM). The ICM contains coil driver circuits that command the coils to operate. The ICM has the following circuits:

    • An ignition voltage circuit
    • A ground
    • An ignition control (IC) 1 control circuit for the 1-4 ignition coil
    • An IC 2 control circuit for the 2-5 ignition coil
    • An IC 3 control circuit for the 3-6 ignition coil
    • A low reference circuit

The powertrain control module (PCM) controls each dual-tower ignition coil by transmitting timing pulses on the ignition coil control circuit to the ICM for the proper coil to enable a spark event.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Remove the fuel pump relay.

    2. Important: Ensure the companion cylinder of the cylinder being tested is grounded.

  2. Test for spark at each cylinder with a J 26792 HEI Spark Tester.

Did you have spark on all cylinders?

--

Go to Step 4

Go to Step 3

3

Is the no spark condition present on all cylinders?

--

Go to Step 8

Go to Step 6

4

Does the spark tester indicate a bright blue spark on all cylinders?

--

Go to Step 5

Go to Step 6

5
  1. Remove the spark plugs. Refer to Spark Plug Replacement .
  2. Examine the spark plugs for any abnormal conditions or damage. Refer to Spark Plug Wire Inspection .

Are the spark plugs in good condition?

--

System OK

Go to Step 20

6

Test the spark plug wires for the following conditions:

    • Proper routing and correct firing order--Refer to Spark Plug Replacement and Spark Plug Wire Replacement .
    • Arching to ground
    • Proper resistance--Refer to Ignition System Specifications .

       Important: If carbon tracking or corrosion is detected, replace both components that are affected.

    • Carbon tracking or corrosion

Did you find and correct the condition?

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Go to Step 23

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Install the spark plugs.
  3. Disconnect the harness connector of the ignition control module (ICM).
  4. Connect the jumper wires from the harness connector of the ICM to the corresponding terminals of the ICM.
  5. Using the jumper wires, exchange the ignition control (IC) circuit of the ICM for the affected ignition coil with a known good ignition coil control circuit of the ICM.
  6. Exchange the spark plug wires of the coils mentioned above.
  7. Start the engine.

Does the cylinder misfire transfer with the suspected ignition coil control circuit?

--

Go to Step 12

Go to Step 14

8
  1. Turn OFF the ignition.
  2. Disconnect the harness connector of the ICM.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp between the ignition voltage circuit of the ICM and good ground. Refer to Circuit Testing .

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 16

9

Connect a test lamp between the ground circuit of the ICM and battery voltage.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 17

10
  1. Turn OFF the ignition.
  2. Remove the fuse that supplies ignition voltage to the ICM.
  3. Measure the resistance of the ignition voltage circuit of the ICM from the fuse to the harness connector of the ICM. Refer to Circuit Testing .

Is the resistance less than the specified value?

3 ohms

Go to Step 11

Go to Step 18

11

Measure the resistance of the ground circuit of the ICM from the harness connector of the ICM to a good ground. Refer to Circuit Testing .

Is the resistance less than the specified value?

3 ohms

Go to Step 14

Go to Step 19

12

Test the ignition coil control circuit of the ICM for high resistance. Refer to Circuit Testing .

Did you find and correct the condition?

--

Go to Step 23

Go to Step 13

13

Test the low reference circuit of the ICM for high resistance. Refer to Circuit Testing .

Did you find and correct the condition?

--

Go to Step 23

Go to Step 15

14

Test for an intermittent and for a poor connection at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 23

Go to Step 21

15

Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 23

Go to Step 22

16

Repair an open or short to ground in the ignition voltage circuit of the ICM. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 23

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17

Repair an open in the ground circuit of the ICM. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 23

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18

Repair the high resistance in the ignition voltage circuit of the ICM. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 23

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19

Repair the high resistance in the ground circuit of the ICM. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 23

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20

Replace the spark plugs. Refer to Spark Plug Replacement .

Did you complete the replacement?

--

Go to Step 23

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21

Replace the ICM and coils assembly. Refer to Ignition Coil Replacement .

Did you complete the replacement?

--

Go to Step 23

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22

Replace the PCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 23

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23
  1. Turn the ignition OFF for 30 seconds.
  2. Start the engine and operate the vehicle.
  3. Observe the vehicle performance and driveability.

Does the vehicle operate normally?

--

System OK

Go to Step 3