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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 DeVille 🢒 Brakes 🢒 Hydraulic Brakes 🢒 Electronic Ignition (EI) System Diagnosis

Circuit Description

The ignition system utilizes an individual module/coil for each spark plug. The following 4 circuits support each ignition module/coil assembly:

    • The ignition 1 voltage circuit
    • The ground circuit
    • The ignition control (IC) circuit
    • The low reference circuit

Each ignition module/coil connects directly to its spark plug through a wire spring conductor internal to the spark plug boot. The IC circuits transmit timing pulses from the powertrain control module (PCM) to each ignition module/coil assembles in the proper sequence for the spark plug firing event. The PCM monitors each IC circuit for improper voltage levels. If an improper voltage level is detected on an IC circuit, a DTC will set.

Diagnostic Aids
    • This electronic ignition (EI) system diagnostic table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test in Engine Electrical.
    • Other electrical, fuel, or mechanical conditions can cause an engine to crank but does not run, or set a DTC P0300 misfire code.
    • An ignition coil, boots, or spark plugs may misfire only when moisture is present. Although difficult to test on this engine, selectively wetting down parts of the ignition system and monitoring for a misfire may help in isolating an intermittent condition. Replace any worn or torn spark plug boots or seals.
    • If the ODD INJ or EVEN INJ fuse opens, this will also result in the loss of ignition 1 voltage to the odd or even ignition coils.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Attempt to start the engine.

Does the engine start and run?

--

Go to Step 21

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Remove the underhood fuse block cover.
  3. Probe both test points of the MDL/COIL fuse in the underhood fuse block with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate on either test point of the fuse?

--

Go to Step 32

Go to Step 4

4
  1. Turn ON the ignition with the engine OFF.
  2. Probe both test points of the MDL/COIL fuse in the underhood fuse block with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors and Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate on both test points of the fuse?

--

Go to Step 11

Go to Step 5

5

Does the test lamp illuminate on one test point of the COIL/MDL fuse?

--

Go to Step 6

Go to Step 40

6
  1. Turn OFF the ignition.
  2. Disconnect the ignition module/coil electrical connector for all 8 cylinders.
  3. Disconnect the 7-way electrical connector at the bank 1 ignition module/coil bracket.
  4. Disconnect the 7-way electrical connector at the bank 2 ignition module/coil bracket.
  5. Replace the MDL/COIL fuse.
  6. Monitor the MDL/COIL fuse.
  7. Turn ON the ignition, with the engine OFF.

Does the MDL/COIL fuse open?

--

Go to Step 33

Go to Step 7

7
  1. Monitor the MDL/COIL fuse.
  2. Connect the 7-way electrical connector for bank 1.

Does the MDL/COIL fuse open?

--

Go to Step 34

Go to Step 8

8
  1. Monitor the MDL/COIL fuse.
  2. Connect the 7-way electrical connector for bank 2.

Does the MDL/COIL fuse open?

--

Go to Step 34

Go to Step 9

9
  1. Monitor the MDL/COIL fuse.
  2. Connect each ignition module/coil electrical connector for bank 1, one at a time.

Does the MDL/COIL fuse open when an ignition module/coil assembly is connected?

--

Go to Step 41

Go to Step 10

10
  1. Monitor the MDL/COIL fuse.
  2. Connect each ignition module/coil electrical connector for bank 2, one at a time.

Does the MDL/COIL fuse open when an ignition module/coil assembly is connected?

--

Go to Step 41

Go to Intermittent Conditions

11
  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the 7-way electrical connector at the bank 2 ignition module/coil bracket.
  3. Probe the ignition 1 voltage circuit terminal that leads from the underhood fuse block with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 13

Go to Step 12

12
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.
  3. Disconnect the underhood fuse block electrical connector that contains the ignition 1 voltage circuit for the bank 2 ignition module/coils.
  4. Measure the resistance of the ignition 1 voltage circuit from the underhood fuse block electrical connector to the 7-way electrical connector with a DMM. Refer to Circuit Testing in Wiring Systems.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 36

Go to Step 40

13
  1. Turn OFF the ignition.
  2. Disconnect the bank 2 ignition module/coils electrical connector.
  3. Measure the resistance of the ignition 1 voltage circuit from the 7-way electrical connector to each ignition module/coil electrical connector with a DMM.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 35

Go to Step 14

14
  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the 7-way electrical connector at the bank 1 ignition module/coil bracket.
  3. Probe the ignition 1 voltage circuit that leads from the underhood fuse block with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 16

Go to Step 15

15
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.
  3. Disconnect the underhood fuse block electrical connector that contains the ignition 1 voltage circuit for the bank 1 ignition module/coils.
  4. Measure the resistance of the ignition 1 voltage circuit from the underhood fuse block electrical connector to the 7-way electrical connector with a DMM.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 36

Go to Step 40

16
  1. Turn OFF the ignition.
  2. Disconnect the bank 1 ignition module/coil electrical connectors.
  3. Measure the resistance of the ignition 1 voltage circuit from the 7-way electrical connector to each ignition module/coil electrical connector with a DMM.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 35

Go to Step 17

17

Measure the resistance of the ground circuit from each ignition module/coil electrical connector on bank 1 to a good engine ground with a DMM.

Does the resistance measure more than the specified value from each ignition module/coil electrical connector?

2 ohms

Go to Step 38

Go to Step 18

18

Measure the resistance of the ground circuit from each ignition module/coil electrical connector on bank 2 to a good engine ground with a DMM.

Does the resistance measure more than the specified value from each ignition module/coil electrical connector?

2 ohms

Go to Step 38

Go to Step 19

19
  1. Disconnect the powertrain control module (PCM) connector J2.
  2. Measure the resistance of the ignition control (IC) low reference circuit on bank 1 from each ignition module/coil electrical connector to the PCM.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 39

Go to Step 20

20

Measure the resistance of the IC low reference circuit on bank 2 from each ignition module/coil electrical connector to the PCM electrical connectors.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 39

Go to Intermittent Conditions

21

Observe the misfire current counters with a scan tool.

Does a cylinder or bank of cylinders indicate an increasing misfire count?

--

Go to Step 22

Go to Diagnostic Aids

22
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.
  3. Disconnect the underhood fuse block electrical connector that contains the ignition 1 voltage circuit for the affected cylinder.
  4. Measure the resistance of the ignition 1 voltage circuit from the underhood fuse block electrical connector to the affected ignition module/coil with a DMM. Refer to Circuit Testing in Wiring Systems.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 37

Go to Step 23

23

Measure the resistance of the ignition 1 voltage bus bar circuit of the underhood fuse block for a high resistance or for an open with a DMM.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 40

Go to Step 24

24

Measure the resistance of the ground circuit from the ignition module/coil electrical connector of the affected cylinder to a good ground with a DMM.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 38

Go to Step 25

25
  1. Disconnect the PCM electrical connector J2.
  2. Measure the resistance of the IC low reference circuit and the IC control circuit between the ignition module/coil electrical connector and the PCM electrical connector with a DMM.

Does the resistance measure greater than the specified value on either circuit?

5 ohms

Go to Step 39

Go to Step 26

26
  1. Turn OFF the ignition.
  2. Disconnect the ignition module/coil assembly from the spark plugs on the bank of cylinders which indicated a misfire condition.
  3. Inspect the ignition module/coil assembly for the following:
    4. • Any visible cracks or deterioration
    • Any carbon tracking or other signs of arcing
    • Any missing or deformed spark plug boot springs
  4. Replace the component if the inspection reveals a condition.

Did you find a condition?

--

Go to Step 43

Go to Step 27

27

Remove the spark plug for the cylinder that was identified as causing a misfire. Refer to Spark Plug Replacement .

Does the spark plug indicate oil contamination?

--

Go to Base Engine Misfire with Excessive Oil Consumption in Engine Mechanical

Go to Step 28

28

Does the spark plug indicate coolant contamination?

--

Go to Base Engine Misfire with Coolant Consumption in Engine Mechanical

Go to Step 29

29
  1. Exchange the suspected spark plug with a spark plug from a different cylinder on the same bank. Refer to Spark Plug Replacement .
  2. Install the ignition module/coil assembly.
  3. Monitor the misfire current counters with a scan tool.
  4. Start the engine.

Does the misfire move with the spark plug exchange?

--

Go to Step 42

Go to Step 30

30
  1. Turn OFF the ignition.
  2. Exchange the ignition module/coil on the cylinder as identified as misfiring with an ignition module/coil assembly from a different cylinder on the same bank.
  3. Monitor the misfire current counters with a scan tool.
  4. Start the engine.

Does the misfire move with the ignition module/coil exchange?

--

Go to Step 41

Go to Step 31

31

Test for an intermittent and for a poor connection at the ignition module/coil electrical connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 43

Go to Base Engine Misfire without Internal Engine Noises in Engine Mechanical

32

Repair the short to battery positive voltage in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 43

--

33

Repair the short to ground in the ignition 1 voltage circuit between the underhood junction block and either bank 1 or bank 2, 7-way electrical connector. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 43

--

34

Repair the short to ground in the ignition 1 voltage circuit between the 7-way electrical connector and the ignition module/coils. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 43

--

35

Repair the high resistance or an open in the ignition 1 voltage circuit between the 7-way electrical connector and the ignition module/coils. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 43

--

36

Repair the high resistance or an open in the ignition 1 voltage circuit between the underhood fuse block electrical connector and the 7-way electrical connector. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 43

--

37

Repair the high resistance or an open in the ignition 1 voltage circuit between the underhood fuse block electrical connector and the ignition module/coil electrical connectors. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 43

--

38

Repair the high resistance or an open in the ground circuit for the ignition module/coil assembly. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 43

--

39

Repair the high resistance or an open in the IC low reference circuit or the IC control circuit between the ignition module/coil assembly and the PCM. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 43

--

40

Replace the underhood fuse block. Refer to Underhood Electrical Center or Junction Block Replacement in Wiring Systems.

Did you complete the replacement?

--

Go to Step 43

--

41

Replace the ignition module/coil assembly. Refer to Ignition Coil Replacement - Bank 1 .

Did you complete the replacement?

--

Go to Step 43

--

42

Replace the spark plug. Refer to Spark Plug Replacement .

Did you complete the replacement?

--

Go to Step 43

--

43

Were you sent to this diagnostic table from the Engine Cranks but Does Not Run diagnostic table?

--

Go to Step 45

Go to Step 44

44

Were you sent to this diagnostic table from the DTC P0300 diagnostic table?

--

Go to Step 46

--

45
  1. Replace any open fuses.
  2. Attempt to start the engine.

Does the engine start and run?

--

Go to Step 47

Go to Engine Cranks but Does Not Run

46
  1. Replace any open fuses.
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 30 seconds.
  4. Operate the vehicle within the conditions for running the DTC P0300. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail during this ignition cycle?

--

Go to DTC P0300

Go to Step 47

47

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK