GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 STS 🢒 Engine 🢒 Engine Controls - 4.6L (LH2) 🢒 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
    • Ignition control (IC) circuit
    • 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 transmits timing pulses from the engine control module (ECM) to each ignition module/coil assembles in the proper sequence for the spark plug firing event. The ECM 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 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 insolating an intermittent condition. Replace any worn or torn spark plug boots or seals.
    • If the ODD coils or EVEN coils fuse opens, this will also result in the loss of ignition 1 voltage to the odd or even fuel injectors.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or 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 37

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Remove the underhood fuse block cover.
  3. Probe both test points of the EVEN coils fuse with a test lamp that is connected to a good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

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

--

Go to Step 9

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Probe both test points of the ODD coils fuse with a test lamp that is connected to a good ground.

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

--

Go to Step 10

Go to Step 5

5
  1. Turn ON the ignition, with the engine OFF.
  2. Probe both test points of the EVEN coils fuse with a test lamp that is connected to a good ground.

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

--

Go to Step 7

Go to Step 6

6

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

--

Go to Step 11

Go to Powertrain Relay Diagnosis

7
  1. Turn ON the ignition.
  2. Probe both test points of the ODD coils fuse with a test lamp that is connected to a good ground.

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

--

Go to Step 19

Go to Step 8

8

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

--

Go to Step 15

Go to Powertrain Relay Diagnosis

9
  1. Turn OFF the ignition.
  2. Disconnect the 7-way electrical connector at the bank 2 ignition coil bracket.
  3. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.
  4. Disconnect the underhood fuse block electrical connector that contains the ignition 1 voltage circuit for the bank 2 coils.
  5. Connect the negative battery cable at the battery.
  6. Probe the ignition 1 voltage circuit for the bank 2 ignition coils at the underhood fuse block electrical connector with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 55

Go to Step 64

10
  1. Turn OFF the ignition.
  2. Disconnect the 7-way electrical connector at the bank 1 ignition coil bracket.
  3. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection in Engine Electrical.
  4. Disconnect the underhood fuse block electrical connector that contains the ignition 1 voltage circuit for the bank 1 coils.
  5. Connect the negative battery cable at the battery.
  6. Probe the ignition 1 voltage circuit for the bank 1 ignition coils at the underhood fuse block electrical connector with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 55

Go to Step 64

11
  1. Turn OFF the ignition.
  2. Replace the EVEN coils fuse.
  3. Disconnect the 7-way electrical connector at the bank 2 ignition module/coil bracket.
  4. Monitor the EVEN coils fuse.
  5. Turn ON the ignition, with the engine OFF.

Does the EVEN coils fuse open?

--

Go to Step 12

Go to Step 13

12
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable. 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 to the bank 2 ignition coils.
  4. Connect the negative cable at the battery.
  5. Replace the EVEN coils fuse.
  6. Monitor the EVEN coils fuse.
  7. Turn ON the ignition, with the engine OFF.

Does the EVEN coils fuse open?

--

Go to Step 64

Go to Step 56

13
  1. Turn OFF the ignition.
  2. Connect the 7-way bank 2 ignition module/coil electrical connector.
  3. Disconnect the electrical connectors at the bank 2 ignition module/coil assemblies.
  4. Monitor the EVEN coils fuse.
  5. Turn ON the ignition, with the engine OFF.

Does the EVEN coils fuse open?

--

Go to Step 57

Go to Step 14

14
  1. Turn ON the ignition, with the engine OFF.
  2. Monitor the EVEN coils fuse.
  3. Connect one bank 2 ignition module/coil electrical connector at a time.

Does the EVEN coils fuse open while connecting a ignition module/coil connector?

--

Go to Step 65

Go to Intermittent Conditions

15
  1. Turn OFF the ignition.
  2. Replace the ODD coils fuse.
  3. Disconnect the 7-way electrical connector at the bank 1 ignition module/coil bracket.
  4. Monitor the ODD coils fuse.
  5. Turn ON the ignition, with the engine OFF.

Does the ODD coils fuse open?

--

Go to Step 16

Go to Step 17

16
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable. 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 to the bank 1 ignition coils.
  4. Connect the negative cable at the battery.
  5. Replace the ODD coils fuse.
  6. Monitor the ODD coils fuse.
  7. Turn ON the ignition, with the engine OFF.

Does the ODD coils fuse open?

--

Go to Step 64

Go to Step 56

17
  1. Turn OFF the ignition.
  2. Connect the 7-way bank 1 ignition module/coil electrical connector.
  3. Disconnect the electrical connectors at the bank 1 ignition module/coil assemblies.
  4. Monitor the ODD coils fuse.
  5. Turn ON the ignition, with the engine OFF.

Does the ODD coils fuse open?

--

Go to Step 57

Go to Step 18

18

  1. Turn ON the ignition, with the engine OFF.
  2. Monitor the ODD coils fuse.
  3. Connect one bank 1 ignition module/coil electrical connector at a time.

Does the ODD coils fuse open while connecting a ignition module/coil connector?

--

Go to Step 65

Go to Intermittent Conditions

19
  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the bank 2 electrical connectors at the ignition module/coils.
  3. Probe the ignition 1 voltage circuit for each ignition module/coil with a test lamp that is connected to a good ground. Refer to Troubleshooting with a Test Lamp or Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate at each ignition module/coil connector?

--

Go to Step 20

Go to Step 21

20
  1. Turn OFF the ignition.
  2. Remove the EVEN coils fuse from the underhood fuse block.
  3. Measure the resistance of the ignition 1 voltage circuit from the underhood fuse block to each ignition module/coil on bank 2 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Does the resistance measure greater than the specified value to each ignition module/coil?

2 ohms

Go to Step 23

Go to Step 25

21
  1. Turn ON the ignition with the engine OFF.
  2. Disconnect the 7-way electrical connector for the ignition module/coils on bank 2.
  3. Probe the ignition 1 voltage circuit that leads from the underhood fuse block, to the 7-way electrical connector with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 58

Go to Step 22

22
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection .
  3. Disconnect the underhood fuse block electrical connector that contains the ignition 1 voltage circuit for the bank 2 ignition module/coils.
  4. Connect the negative battery cable at the battery.
  5. Connect a 20-amp fused jumper wire from the battery positive voltage to the ignition 1 voltage circuit terminal at the underhood fuse block electrical connector. Refer to Using Fused Jumper Wires in Wiring Systems.
  6. Probe the ignition 1 voltage circuit at the 7-way bank 2 electrical connector 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 24

Go to Step 59

23
  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 each ignition module/ coil on bank 2 with a DMM.

Does the resistance measure greater than the specified value to each ignition module/coil?

2 ohms

Go to Step 60

Go to Step 24

24

Measure the resistance of the underhood fuse block ignition 1 voltage circuit for the bank 2 ignition module/coil with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Does the resistance measure more than the specified value?

2 ohms

Go to Step 64

Go to Intermittent Conditions

25
  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the bank 1 electrical connectors at the ignition module/coils.
  3. Probe the ignition 1 voltage circuit for each ignition module/coil with a test lamp that is connected to a good ground.

Does the test lamp illuminate at each ignition module/coil connector?

--

Go to Step 26

Go to Step 27

26
  1. Turn OFF the ignition.
  2. Remove the ODD coils fuse from the underhood fuse block.
  3. Measure the resistance of the ignition 1 voltage circuit from the underhood fuse block to each ignition module/coil on bank 1 with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Does the resistance measure greater than the specified value to each ignition module/coil?

2 ohms

Go to Step 29

Go to Step 31

27
  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the 7-way bank 1 ignition module/coil electrical connector.
  3. Probe the ignition 1 voltage circuit that leads from the underhood fuse block to the 7-way connector with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 58

Go to Step 28

28
  1. Turn OFF the ignition.
  2. Disconnect the negative battery cable at the battery. Refer to Battery Negative Cable Disconnection and Connection .
  3. Disconnect the underhood fuse block electrical connector that contains the ignition 1 voltage circuit for the bank 1 ignition module/coils.
  4. Connect the negative battery cable at the battery.
  5. Connect a 20-amp fused jumper wire from battery positive voltage to the ignition 1 voltage circuit at the underhood fuse block. Refer to Using Fused Jumper Wires in Wiring Systems.
  6. Probe the ignition 1 voltage circuit at the 7-way bank 1 electrical connector 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 30

Go to Step 59

29
  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 each ignition module/ coil on bank 1 with a DMM.

Does the resistance measure greater than the specified value to each ignition module/coil?

2 ohms

Go to Step 60

Go to Step 30

30

Measure the resistance of the underhood fuse block ignition 1 voltage circuit for the bank 1 ignition module/coil with a DMM. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 64

Go to Intermittent Conditions

31
  1. Turn OFF the ignition.
  2. Disconnect the electrical connectors at the bank 2 ignition module/coils assembly.
  3. Probe the ground circuit for each bank 2 ignition module/coil with a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 32

Go to Step 61

32

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. Refer to Troubleshooting with a Digital Multimeter in Wiring Systems.

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

2 ohms

Go to Step 61

Go to Step 33

33
  1. Turn OFF the ignition.
  2. Disconnect the electrical connectors at the bank 1 ignition module/coils assembly.
  3. Probe the ground circuit at each bank 1 ignition module/coil electrical connector with a test lamp that is connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 34

Go to Step 61

34

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 greater than the specified value from each ignition module/coil?

2 ohms

Go to Step 61

Go to Step 35

35
  1. Turn OFF the ignition.
  2. Disconnect the bank 2 electrical connector at each of the ignition module/coils.
  3. Disconnect the electrical connector at the engine control module (ECM) that contains the low reference circuit for bank 2.
  4. Measure the resistance of the EST low reference circuit from each ignition module/coil to the ECM with a DMM. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 62

Go to Step 36

36
  1. Disconnect the bank 1 electrical connector at each ignition module/coil.
  2. Measure the resistance of the EST low reference circuit from each ignition module/coil to the ECM with a DMM.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 62

Go to Step 67

37

Observe the misfire current counters with a scan tool.

Does a cylinder indicate an increasing misfire count?

--

Go to Step 38

Go to Intermittent Conditions

38
  1. Turn ON the ignition, with the engine OFF.
  2. Remove the underhood fuse block cover.
  3. Probe both test points of the fuse for the bank of cylinders that are identified as misfiring with a test lamp that is connected to a good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

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

--

Go to Step 44

Go to Step 39

39

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

--

Go to Step 40

Go to Powertrain Relay Diagnosis

40
  1. Turn OFF the ignition.
  2. Replace the open fuse for the bank of cylinders identified as misfiring.
  3. Disconnect the 7-way electrical connector for the bank of cylinders identified as misfiring at the ignition module/coil bracket.
  4. Turn ON the ignition with the engine OFF.

Does the fuse open?

--

Go to Step 41

Go to Step 42

41
  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 to the bank of cylinders identified as misfiring.
  4. Replace the open fuse.
  5. Connect the negative battery cable at the battery.
  6. Turn ON the ignition, with the engine OFF.

Does the fuse open?

--

Go to Step 64

Go to Step 56

42
  1. Turn OFF the ignition.
  2. Connect the 7-way electrical connector at the ignition module/coil bracket.
  3. Disconnect the electrical connectors at the ignition module/coil assemblies on the bank of cylinders identified as misfiring.
  4. Turn ON the ignition with the engine OFF.

Does the fuse open?

--

Go to Step 57

Go to Step 43

43
  1. Turn ON the ignition, with the engine OFF.
  2. Monitor the fuse for the bank of cylinders identified as misfiring.
  3. Connect each ignition module coil electrical connector one at a time.

Does the fuse open while connecting an ignition module/coil connector?

--

Go to Step 65

Go to Intermittent Conditions

44
  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 60

Go to Step 45

45

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

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 64

Go to Step 46

46

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 61

Go to Step 47

47
  1. Disconnect the ECM electrical connector that contains the ignition coil control circuit for the affected cylinder.
  2. Measure the resistance of the ignition coil control circuit between the ignition module/coil electrical connector of the affected cylinder and the ECM electrical connector.

Does the resistance measure more than the specified value?

2 ohms

Go to Step 63

Go to Step 48

48
  1. Disconnect the ECM electrical connectors.
  2. Measure the resistance of the low reference circuit from the ignition module/coil electrical connector to the ECM electrical connector with a DMM.

Does the resistance measure greater than the specified value?

2 ohms

Go to Step 62

Go to Step 49

49
  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, deterioration or other damage.
    • Any carbon tracking or other signs of arcing.
    • Any missing or damage spark plug boot springs.
  4. Replace the component if the inspection reveals a condition.

Did you find a condition?

--

Go to Step 67

Go to Step 50

50

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 51

51

Does the spark plug indicate coolant contamination?

--

Go to Base Engine Misfire with Coolant Consumption in Engine Mechanical

Go to Step 52

52
  1. Exchange the suspected spark plug with a spark plug from a different cylinder on the same bank. Refer to Spark Plug Replacement .
  2. Reinstall 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 66

Go to Step 53

53
  1. Turn OFF the ignition.
  2. Exchange the ignition module/coil on the cylinder identified as misfiring with a 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 65

Go to Step 54

54

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 67

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

55

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 67

--

56

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

Did you complete the repair?

--

Go to Step 67

--

57

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 67

--

58

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 67

--

59

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 67

--

60

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 67

--

61

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 67

--

62

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

Did you complete the repair?

--

Go to Step 67

--

63

Repair the high resistance in the ignition coil control circuit.

Did you complete the repair?

--

Go to Step 67

--

64

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 67

--

65

Replace the ignition module/coil assembly. Refer to Ignition Coil Replacement - Bank 1 or Ignition Coil Replacement - Bank 2 .

Did you complete the replacement?

--

Go to Step 67

--

66

Replace the spark plug. Refer to Spark Plug Replacement .

Did you complete the replacement?

--

Go to Step 67

--

67

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

--

Go to Step 69

Go to Step 68

68

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

--

Go to Step 70

--

69
  1. Replace any open fuses.
  2. Attempt to start the engine.

Does the engine start and run?

--

Go to Step 71

Go to Engine Cranks but Does Not Run

70
  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 this ignition?

--

Go to DTC P0300

Go to Step 71

71

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