GM Service Manual Online
For 1990-2009 cars only

Refer to

Ignition Control


Object Number: 23097  Size: FS
Engine Controls Components
Electronic Ignition (EI) System
Fuel Injection Control
PCM Power, Grounds, MIL Control, Serial Data
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
.

Circuit Description

The Electronic Ignition system uses a waste spark method of spark distribution. In this type of ignition system, the ignition control module triggers the correct coil based on the 7X signal received from the crankshaft position sensor, resulting in both spark plugs connected to the coil firing at the same time. The spark plug for the cylinder on the exhaust stroke requires a lower energy requirement to fire, leaving the remaining high voltage to fire the spark plug for the cylinder on the compression stroke.

During cranking, the ignition control module monitors the 7X crankshaft position sensor input for recognition of the sync signal. The sync signal is used to determine the correct cylinder pair to spark first. After the sync signal has been processed by the ignition control module, it sends a 3X reference signal to the PCM. The sync signal is used only by the ignition control module. It is used for spark synchronization at start-up only (not passed to the PCM).

When the ignition switch is turned to the ON position, the PCM commands all six injectors to open for one priming shot of fuel in all cylinders. After priming, the injectors are left OFF for the next six 3X reference signals from the ignition control module (two crankshaft revolutions). This allows each cylinder to use the fuel from the priming shot. During this waiting period, a cam signal will have been received by the PCM. Once true camshaft position is detected, the PCM operates the injectors sequentially. However, if the cam signal is not present at start-up, DTC P0341 will set and the PCM will start sequential fuel delivery in random pattern with a 1 in 6 chance that fuel delivery is correct.

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following items:

    • Poor connection or damaged harness. Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.
    • Faulty Engine Coolant Temperature Sensor. Using a scan tool, compare Engine Coolant Temperature with Intake Air Temperature on a completely cool engine. Engine Coolant Temperature should be within 10° C of Intake Air Temperature. If not, replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement .

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. If spark is present, the ignition control module, coils, and ignition wires for cylinders 2, 4 and 6 are operating properly.

  2. No spark from all of the coils indicate a problem with the ignition control module or 7X CKP sensor.

  3. If resistance is within specifications, then a possible intermittent fault is present (refer to Diagnostic Aids).

  4. Verifies the condition of the ignition wires for cylinders 1,3 and 5. An open ignition wire results in the loss of two cylinder. A no start may occur especially at colder ambient temperatures.

  5. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

Engine Cranks But Will Not Run

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

2

Select Failed last test with the scan tool.

Are any of the following DTCs set?

--

Diagnose the applicable DTC

Go to Step 3

3

  1. Turn OFF the ignition switch, install a fuel pressure gage at the fitting on the fuel rail.
  2. Turn ON the ignition switch, observe the fuel pressure

Is the fuel pressure within the specified values and holding?

284-325 kPa (41 - 47 PSI)

Go to Step 5

Go to Step 4

4

Is any fuel pressure indicated?

--

Refer to Fuel System Diagnosis

Refer to Fuel Pump Electrical Circuit Diagnosis

5

  1. Check the fuse for the fuel injector feed circuit.
  2. If the fuse is blown, check for the following conditions:
  3. • A short to ground in the fuel injector feed circuit.
    • A shorted injector.

       Important: Removal of the upper intake manifold is required to access the fuel injectors. Refer to Upper Intake Manifold .

  4. If a problem is found, repair it as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 6

6

  1. Check for the following conditions:
  2. • open in the fuel injector feed circuit.
    • Poor connection at the 10-way fuel injector/engine harness.
  3. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 7

7

  1. Turn OFF the ignition switch, disconnect the 10-way fuel injector/engine harness connector.
  2. Install test light J 35616-200 between B+ and each injector driver circuit.
  3. Observe the test light while cranking the engine.

Does the test light blink?

--

Go to Step 9

Go to Step 8

8

  1. Check for the following circuit conditions:
  2. • Open fuel injector driver circuit(s).
    • Poor connections at the PCM.
  3. If a problem is found, repair as necessary. Refer to Repair Procedures in electrical Diagnosis.

Was a problem found?

 

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 30

9

  1. Remove the 15 AMP fuel injection fuse from the underhood electrical center.
  2. Install spark tester J 26792 in the 2, 4, and 6 cylinder ignition wires (one at a time).
  3. Connect one end of a good ignition wire to the coil tower of each companion cylinder. The companion cylinder is the cylinder that shares the same ignition coil (i.e., 1/4; 2/5; 3/6).
  4. Connect the other end of the good ignition wire to engine ground.
  5. Crank the engine while observing the spark tester. A crisp, blue spark should be observed.

Do the coils provide spark?

--

Go to Step 21

Go to Step 10

10

Do all of the coils fail to provide spark?

--

Go to Step 11

Go to Step 16

11

  1. Check for a blown fuse to the electronic ignition control module ignition feed circuit.
  2. If the fuse is blown, check for a short between the ignition control module feed circuit and the following locations:
  3. • Engine ground
    • Ignition control module ground
    • IC Control circuit
    • Reference Low circuit
  4. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was the fuse blown?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 12

12

  1. Check for an open in the electronic ignition control module feed and ground circuits.
  2. If a problem is found, repair it as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 13

13

  1. Turn OFF the ignition.
  2. Disconnect the 2 wire, 7X CKP sensor (PPL and YEL wires) connector from the ICM.
  3. Connect a DMM between the 7X CKP sensor harness connector terminals.
  4. Set the DMM to read ohms.

Is the resistance between the specified value?

800-1,200 ohms

Go to Step 15

Go to Step 14

14

  1. Turn OFF the ignition switch.
  2. Check the 7X CKP circuit for the following conditions:
  3. • An open circuit
    • A short to ground
    • A short to voltage
    • 7X wiring harness shorted together.
    • Poor connections at 7X crankshaft position sensor
  4. If a problem is found, repair it as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 27

15

  1. Check for poor connections at the ICM.
  2. If a problem is found, repair it as necessary. Refer to Repair Procedures in Electrical Diagnosis.

Was a problem found?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 29

16

  1. Measure the ignition coil secondary resistance associated with the cylinders that did not have spark.
  2. If any resistance is outside the specified values, replace faulty ignition coil(s) as necessary. Refer to Ignition Control Module Replacement .

Did any ignition coils require replacement?

Between 5000 and 8000 ohms (5K and 8K ohms).

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 17

17

  1. Remove and visually/physically inspect the ignition coil(s) associated with the cylinders that did not have spark. Ensure that the coils and coil towers are free of cracks and carbon tracking.
  2. If a problem is found, replace damaged ignition coil(s) as necessary. Refer to Ignition Control Module Replacement .

Did your inspection reveal a problem?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 18

18

  1. Connect a test light across the ignition module primary circuit (between the electronic ignition control module terminals) for coil(s) associated with the cylinders which did not have spark.
  2. Observe the test light while cranking the engine.

Does the test light blink while the engine is being cranked?

--

Go to Step 19

Go to Step 29

19

  1. Visually/physically inspect the ignition wires associated with the cylinders that did not have spark. Ensure that the wires and boots are free of carbon tracking and the insulation is not damaged.
  2. If a problem is found, replace faulty ignition wire(s) as necessary.

Did inspection reveal any faulty ignition wires?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 20

20

  1. Measure the resistance of the ignition wires associated with the cylinders that did not have spark.
  2. If any resistance is outside the specified value, replace the faulty ignition wire.

Was a problem found?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Refer to Diagnostic Aids

21

  1. Check for a stuck TP sensor, faulty ECT sensor, or a skewed or stuck MAP sensor (refer to Diagnostic Aids).
  2. If a problem is found, repair as necessary.

Was a problem found?

 

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 22

22

  1. Visually/physically inspect the 1, 3, and 5 cylinder ignition wires. Ensure that the wires and boots are free of carbon tracking and the insulation is not damaged.
  2. If a problem is found, replace faulty ignition wire(s) as necessary.

Did inspection reveal any faulty ignition wires?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 23

23

  1. Measure the resistance of the 1, 3, and 5 cylinder ignition wires.
  2. If any resistance is outside the specified value, replace the faulty ignition wire.

Was a problem found?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Go to Step 24

24

Remove all the spark plugs and inspect the electrodes.

Does your inspection reveal any spark plugs exhibiting excessive fouling?

--

Go to Step 26

Go to Step 25

25

  1. Test the fuel for contamination. Refer to Alcohol/Contaminants-in-Fuel Testing Procedure .
  2. If a problem is found, clean the fuel system and correct the contaminated fuel condition as necessary.

Was a problem found?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

Refer to Diagnostic Aids

26

Repair engine mechanical problem. Refer to Engine Mechanical Diagnosis to diagnose the following conditions:

    • Bent push rods;
    • Faulty or incorrect camshaft;
    • Leaking or sticky valves or rings;
    • Excessive valve deposits;
    • Loose or worn rocker arms;
    • Weak valve springs;
    • Incorrect valve timing;
    • Leaking head gasket;

Is action complete?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

--

27

Replace the 7X crankshaft position sensor. Refer to Crankshaft Position Sensor Replacement .

Is action complete?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

--

28

Replace the ignition coil(s) associated with the cylinders that did not have spark. Refer to Ignition Control Module Replacement .

Is action complete?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

--

29

Replace the electronic ignition control module. Refer to Ignition Control Module Replacement .

Is action complete?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

--

30

Replace the PCM.

Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Is action complete?

--

Go to the Powertrain On Board Diagnostic (OBD) System Check

--