GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 Safari - 4WD 🢒 Engine 🢒 Engine Electrical 🢒 Distributor Ignition (DI) System Diagnosis

System Description

This system includes the distributor, the camshaft position (CMP) sensor , the ignition coil with the ignition control (IC) module, the secondary wires, the spark plugs, the knock sensors (KS), and the crankshaft position (CKP) sensor. The ignition system is controlled by the powertrain control module (PCM). The PCM monitors the information from various engine sensors, computes the desired spark timing, and controls the dwell and firing of the ignition coil via an IC line to the IC module.

Diagnostic Aids

Check the following when the distributor rotor does not rotate, while engine is cranking:

    • A broken distributor drive shaft
    • A worn distributor drive gear or camshaft timing chain and gears

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

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

  1. This step is testing for an internally shorted camshaft position sensor.

    2.

  2. This step is testing for the presence of battery positive voltage at the camshaft and crankshaft electrical connectors.

    3.

  3. This step checks for proper spark output. The spark test requires a minimum of 25,000 volts to operate. This check can be used in case of an ignition miss, because the system may provide enough voltage to run the engine but not enough to operate a spark plug under heavy load.

    4.

  4. This test separates the distributor cap, rotor, and ignition wires from the ignition coil in order to help identify a secondary ignition system problem.

    5.

  5. This test checks the ignition control module, connections, and wiring.

    6.

  6. This test begins to determine if the PCM is providing a signal to the ignition control module. If the PCM is not providing a signal to the ignition control module, the problem exists between the ignition control module and the PCM.

    7.

  7. This test checks for a basic engine mechanical problem.

Step

Action

Value(s)

Yes

No

Schematic Reference: Engine Controls Schematics

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 the scan tool.

Does the scan tool display RPM?

--

Go to Step 7

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the camshaft position (CMP) sensor electrical connector.
  3. Attempt to start the engine.

Does the engine start and continue to run?

--

Go to Step 23

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the crankshaft position (CKP) sensor electrical connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage of the 12-volt reference circuit at the CKP and the CMP sensor electrical connectors. Refer to Measuring Voltage in Wiring Systems.

Does the voltage equal the specified value for both circuits?

B+

Go to Step 24

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Test the CKP sensor 12-volt reference circuit for an open circuit or for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Test the CMP sensor 12-volt reference circuit for an open circuit or for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 28

7

  1. Inspect the spark plug wires for open circuits, cracks, or improper seating of terminals at the spark plugs, distributor, and ignition coil before proceeding with the test.
  2. Inspect the spark at the plug with the J 26792 Spark Tester or equivalent while cranking. If there is no spark on one wire, check a second wire. A few sparks then nothing is considered no spark.

Does spark occur on all cylinders?

--

Go to Intermittent Conditions

Go to Step 8

8

  1. Remove the coil wire from the distributor cap.
  2. Insert the J 26792 into coil wire and clamp the tester onto a ground.
  3. Crank the engine.

Does spark occur?

--

Go to Step 17

Go to Step 9

9

Measure the coil wire resistance.

Does the resistance measure approximately the specified value?

1,000 ohms/ft

Go to Step 10

Go to Step 39

10

  1. Disconnect the ignition coil harness connector.
  2. Probe the harness ignition coil driver circuit with a test lamp connected to battery positive voltage.
  3. Crank the engine.

Does the test lamp flash while cranking the engine?

--

Go to Step 12

Go to Step 11

11
  1. Turn OFF the ignition.
  2. Probe the harness ignition coil driver circuit with a test lamp connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 34

Go to Step 13

12
  1. Turn ON the ignition, with the engine OFF.
  2. Measure the coil ignition 1 voltage with a DMM connected to a ground.

Does the voltage measure above the specified value?

10 V

Go to Step 27

Go to Step 22

13
  1. Turn OFF the ignition.
  2. Inspect for an open or short to voltage between the ignition coil and the IC module.

Did you find the condition?

--

Go to Step 33

Go to Step 14

14
  1. Turn ON the ignition, with the engine OFF.
  2. Measure the ignition 1 voltage at the IC module harness connector with a DMM connected to a ground.

Does the voltage measure above the specified value?

10 V

Go to Step 15

Go to Step 25

15

Probe the IC module harness connector ground circuit with a test lamp connected to battery positive voltage.

Does the test lamp illuminate?

--

Go to Step 16

Go to Step 29

16

  1. Probe the IC timing control circuit with a DMM set to the AC scale connected to a ground.
  2. Crank the engine.
  3. Observe the voltage while the engine is being cranked.

Does the voltage measure within the specified values?

1-4 V

Go to Step 26

Go to Step 19

17

  1. Remove the distributor cap.
  2. Inspect the cap for the following conditions:
    3. • Cracks
    • Moisture
    • Carbon tracks
    • Physical damage
  3. For more in-depth procedures, refer to Distributor Inspection .

Did you find any of these conditions?

--

Go to Step 41

Go to Step 18

18

  1. Crank the engine.
  2. Observe the distributor rotor while the engine is being cranked.

Did the distributor rotor turn?

--

Go to Step 40

Go to Diagnostic Starting Point - Engine Mechanical in Engine Mechanical.

19
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Inspect the ignition timing control circuit for an open between the PCM and the IC module.

Did you find the condition?

--

Go to Step 30

Go to Step 20

20

Probe the ignition timing control circuit at the PCM with a test lamp connected to battery voltage.

Does the test lamp illuminate?

--

Go to Step 31

Go to Step 21

21
  1. Turn ON the ignition, with the engine OFF.
  2. Probe the ignition timing control circuit at the PCM with a test lamp connected to a ground.

Does the test lamp illuminate?

--

Go to Step 32

Go to Step 28

22
  1. Inspect for an open or shorted to ground ignition 1 voltage circuit at the ignition coil.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 44

--

23

Inspect for poor or intermittent connections at the CMP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 35

24

Inspect for poor or intermittent connections at the CKP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 36

25
  1. Inspect for an open or a short to ground on the ignition 1 voltage circuit at the IC module.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 44

--

26

Inspect for a poor IC module connection.

Did you find a problem?

--

Go to Step 37

Go to Step 42

27

Inspect for a poor coil connection.

Did you find a problem?

--

Go to Step 37

Go to Step 38

28

Inspect for a poor PCM connection.

Did you find a problem?

--

Go to Step 37

Go to Step 43

29

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

Did you complete the repair?

--

Go to Step 44

--

30

Repair the open ignition timing control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 44

--

31

Repair the grounded ignition timing control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 44

--

32

Repair the short to voltage in the ignition timing control circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 44

--

33

Repair the open or short to voltage in the coil driver circuit between the ignition coil and the IC module. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 44

--

34

Repair the short to ground in the coil driver circuit between the ignition coil and the IC module. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 44

--

35

Replace the CMP sensor. Refer to Camshaft Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 44

--

36

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

Did you complete the replacement?

--

Go to Step 44

--

37

Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 44

--

38

Replace the ignition coil. Refer to Ignition Coil Replacement .

Did you complete the replacement?

--

Go to Step 44

--

39

Replace the coil wire. Refer to Spark Plug Wire Replacement .

Did you complete the replacement?

--

Go to Step 44

--

40

Replace the distributor rotor. Refer to Distributor Overhaul .

Did you complete the replacement?

--

Go to Step 44

--

41

Replace the distributor cap. Refer to Distributor Overhaul .

Did you complete the replacement?

--

Go to Step 44

--

42

Replace the IC module. Refer to Ignition Control Module Replacement .

Did you complete the replacement?

--

Go to Step 44

--

43

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 44

--

44

Operate the vehicle within the conditions under which the original symptom was noted.

Does the system now operate properly?

--

System OK

Go to Step 1