GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The electronic ignition system uses an individual ignition coil for each cylinder. The powertrain control module (PCM) controls the ignition operation through eight individual ignition control (IC) circuits. Each bank of four ignition coils is connected to the PCM, power, or ground by the following circuits:

    • Low reference
    • Chassis ground
    • Ignition 1 voltage
    • The appropriate IC circuit

The PCM triggers an ignition coil by grounding the appropriate IC circuit using information from the crankshaft position (CKP) and camshaft position (CMP) sensors.

Diagnostic Aids

Important: A missing CMP sensor signal may cause a long crank condition.

The CKP signal must be available for the engine to start. The CMP signal is not needed to start and operate the engine. The PCM can determine when a cylinder is on either the firing or exhaust stroke by the 24X signal.

Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

The 12-volt reference circuit for the CKP and the CMP sensors are shared internally in the PCM.

For an intermittent condition, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Monitoring the misfire current counters determines if a fault is present.

  2. A good indication that the fuse is open is all off the misfire current counters are incrementing on one side of the engine. Inspect the ignition positive voltage circuit for a grounded circuit. If the fuse is open and the ignition coil circuits are OK, inspect the injector circuits for being grounded.

Step

Action

Value(s)

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Crank the engine.
  2. Observe the engine speed parameter with a scan tool.

Does the scan tool display engine RPM?

--

Go to Step 3

Go to Step 16

3

Is DTC P0335, P0336, or P0351-P0358 also set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 4

4

Attempt to start the engine.

Does the engine start and run?

--

Go to Step 5

Go to Step 9

5

  1. Idle the engine.
  2. Observe the misfire current counters on the scan tool.

Does the scan tool display any misfire current counters incrementing?

--

Go to Step 6

Go to Diagnostic Aids

6

Do the misfire current counters increment for most cylinders on one bank of the engine?

--

Go to Step  12

Go to Step 7

7

  1. Inspect the spark plug wire for open circuits, cracks, or improper seating of terminals at the spark plug or coil before proceeding with test. Refer to Spark Plug Wire Inspection .
  2. Inspect for spark at the plug with the J 26792 Spark Tester or equivalent while cranking. A few sparks, then nothing is considered no spark.

Is adequate spark present?

--

Go to Step 33

Go to Step 8

8

Measure the spark plug wire resistance. Refer to Spark Plug Wire Inspection .

Is the resistance more than the specified value?

1,000 ohms/ft

Go to Step 32

Go to Step 9

9

  1. Turn OFF the ignition.
  2. Disconnect the ignition coil that corresponds to the Misfire Current counter that was incrementing.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 1 voltage circuit of the ignition coil with a test lamp connected to a good ground. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step  10

Go to Step 13

10

Probe the ignition 1 voltage circuit at the ignition coil with a test lamp connected to the ground circuit of the ignition coil. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step  11

Go to Step 14

11

Probe the ignition 1 voltage circuit at the ignition coil with a test lamp connected to the low reference circuit of the ignition coil. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step  20

Go to Step 15

12

Inspect for an open ENG 2 or ENG 3 fuse.

Is the fuse open?

--

Go to Step 29

Go to Step  23

13

  1. Disconnect the main ignition coil 8-way connector.
  2. Probe the ignition 1 voltage circuit at the ignition coil main 8-way connector using the test lamp connected to battery ground. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 24

Go to Step 23

14

  1. Disconnect the main ignition coil 8-way connector.
  2. Probe the ignition 1 voltage circuit on the harness side with a test lamp connected to the ground circuit of the ignition coil. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step  18

Go to Step  26

15

  1. Disconnect the main ignition coil 8-way connector.
  2. Probe the ignition 1 voltage circuit on the harness side with a test lamp connected to the low reference circuit of the ignition coil. Refer to Probing Electrical Connectors in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 19

Go to Step  28

16

  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the crankshaft position (CKP) sensor.
  3. Measure the voltage from the CKP sensor 12-volt reference circuit and a good ground with the DMM.
  4. Compare the measured voltage with the system voltage.

Is the difference in the voltage more than the specified value?

0.5 V

Go to Step 17

Go to Step 21

17

Test for a short to ground in the CKP 12-volt reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step 22

18

Test for an intermittent and for a poor connection at the ignition coil 8-way 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 35

Go to Step  25

19

Test for an intermittent and for a poor connection at the ignition coil 8-way 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 35

Go to Step  27

20

Test for an intermittent and for a poor connection at the ignition coil. 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 35

Go to Step 31

21

Test for an intermittent and for a poor connection at the CKP sensor. 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 35

Go to Step 30

22

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 in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 35

Go to Step  34

23

Repair the open or high resistance in the ignition 1 voltage circuit between the fuse block and the splice. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 35

--

24

Repair the open or high resistance in the ignition 1 voltage circuit between the splice and the ignition coil connector. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 35

--

25

Repair the open in the ground circuit between the main 8-way connector and the ignition coil. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 35

--

26

Repair the open in the ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 35

--

27

Repair the open in the low reference circuit between the main 8-way connector and the ignition coil. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 35

--

28

Repair the open in the low reference circuit between the PCM and the splice. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 35

--

29

  1. Repair the ignition 1 voltage for a short to ground. Refer to Wiring Repairs in Wiring Systems.
  2. Replace the fuse.

Did you complete the repair?

--

Go to Step 35

--

30

Replace the CKP sensor. Refer to Crankshaft Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 35

--

31

Replace the ignition coil. Refer to Ignition Coil Replacement .

Did you complete the replacement?

--

Go to Step 35

--

32

Replace the spark plug wire. Refer to Spark Plug Wire Replacement .

Did you complete the replacement?

--

Go to Step 35

--

33

Replace the spark plug. Refer to Spark Plug Replacement .

Did you complete the replacement?

--

Go to Step 35

--

34

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 35

--

35

Attempt to start the engine.

Does the engine start and continue to run?

--

Go to Step 36

Go to Step 2

36

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the engine for 30 seconds.
  3. Start the engine.
  4. Allow the engine to reach operating temperature.

Are there any DTCs that have not been diagnosed?

--

System OK

Go to Diagnostic Trouble Code (DTC) List