GM Service Manual Online
For 1990-2009 cars only

Refer to

Ignition Control Module, CMP and CKP


Object Number: 378473  Size: FS
Cell 10: Underhood Accessory Wiring Junction Block
Fuel Pump and Fuel Level Sensors
Power, Ground, DLC and MIL
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Engine Controls Components

Refer to

Fuel Injectors


Object Number: 378479  Size: FS
Cell 10: Underhood Accessory Wiring Junction Block
Engine Data Sensors
Fuel Pump and Fuel Level Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Engine Controls Components
.

Circuit Description

The Electronic Ignition system uses a waste spark method of spark distribution. The ignition control module (ICM) determines the correct coil sequence based on the CKP sync signal received from the crankshaft position sensor. Two spark plugs connected to the coil fire at the same time. The cylinder on the compression stroke (event cylinder) uses most of the coil's available voltage to fire the spark plug. The cylinder on the exhaust stroke (waste cylinder) uses the remaining coil energy to fire the spark plug.

During crank, the ICM monitors the 18X CKP and CKP sync signals. The ICM uses CKP sync signal to determine the correct cylinder pair to fire first. Only the ICM uses the CKP sync signal. The ICM does not pass the CKP signal to the PCM. While the ICM processes the CKP sync signal, the ICM also monitors the 18X CKP signal. The ICM uses the 18X signal for crankshaft position information and to generate 3X reference pulses. The ICM sends the 18X and 3X reference pulses to the PCM. When the PCM receives these pulses, the PCM energizes all six injectors to allow a priming shot of fuel for the cylinders. After priming the cylinders, the PCM shuts the injectors OFF for the next six, 3X reference pulses. This allows each cylinder a chance to use the fuel from the priming shot. During this waiting period, the PCM receives a camshaft position (CMP) signal pulse. The CMP signal allows the PCM to calculate true sequential fuel injection. If a loss of the CMP signal occur during start-up, the PCM still operates the fuel injectors sequentially. However, fuel injection occurs with a 1 in 6 chance that the injector sequencing 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

The numbers below refer to the step numbers on the Diagnostic Table:

  1. Determines if the ignition control module (ICM) is receiving the 18X CKP reference signal. If the 18X CKP signal to the ICM is not present, there are no RPM, spark, or fuel injector pulses.

  2. Ensures that the ICM has the proper voltage supply and ground.

  3. Verifies that the ICM is supplying the proper sensor feed voltage.

  4. Test for the proper operation of the CKP sync signal, ICM and related spark system components. Without the CKP sync signal the ICM is unable to properly sequence the ignition coils.

  5. If the 18X and CKP sync signals to the ICM or the 18X and 3X reference signals to the ICM short together the vehicle does not start and run. However, there are spark and fuel injector pulses.

  6. This vehicle is equipped with a PCM which utilizes an electrically erasable programmable read-only memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.

Engine Cranks But Will Not Run

Step

Action

Value(s)

Yes

No

1

Did you complete the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step  2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: Before proceeding with this diagnostic, ensure that the vehicle's battery is fully charged.

Important: If any DTCs are stored as Failed Since Code Clear, diagnose the DTCs before continuing with this table.

  1. Inspect the fuses which supply ignition positive voltage to the following components:
  2. • The electronic ignition control module.
    • The fuel injectors.
  3. If either fuse is blown, locate and repair a short to ground in the faulty ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 3

3

  1. Turn off the ignition switch.
  2. Install a fuel pressure gauge at the fitting on the fuel rail.
  3. Turn on the ignition switch.
  4. Observe the fuel pressure gauge.

Is the fuel pressure holding within the specified range?

333-376 kPa (48-55 psi)

Go to Step 5

Go to Step  4

4

Is any fuel pressure indicated?

--

Go to Fuel System Pressure Test

Go to Fuel Pump Electrical Circuit Diagnosis

5

  1. Turn off the ignition switch.
  2. Remove the fuel pressure gauge from the fuel rail.
  3. Connect the scan tool.
  4. Turn on the ignition switch.
  5. Select the Engine Data 1 display on the scan tool.
  6. Observe the engine RPM while cranking the engine.

Does the scan tool indicate an engine RPM?

--

Go to Step 17

Go to Step 6

6

  1. Turn off the ignition switch.
  2. Disconnect the ignition control module (ICM) connector.
  3. Turn on the ignition switch.
  4. Connect a test lamp between the ignition positive feed terminal and the ground terminal in the ICM connector.

Does the test lamp illuminate?

--

Go to Step  8

Go to Step  7

7

  1. Leave the ICM connector disconnected.
  2. Connect the test lamp between the ignition positive feed and engine ground.

Does the test lamp illuminate?

--

Go to Step  39

Go to Step 40

8

  1. Turn off the ignition switch.
  2. Reconnect the ICM connector.
  3. Disconnect the 18X crankshaft position (CKP) sensor connector.
  4. Turn on the ignition switch.
  5. Connect a digital multimeter (DMM) between the 18X CKP sensor feed terminal and the sensor ground terminal in the connector.

Is the voltage near the specified value?

B+

Go to Step 9

Go to Step 11

9

Connect the DMM between the 18X CKP sensor signal terminal and sensor ground terminal in the connector.

Is the voltage within the specified range?

6-8 V

Go to Step 10

Go to Step 14

10

Inspect for faulty terminal connections at the 18X CKP sensor.

If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 41

11

Connect the DMM between the 18X CKP sensor feed and engine ground.

Is the voltage near the specified value?

B+

Go to Step 12

Go to Step 13

12

  1. Turn off the ignition switch.
  2. Leave the 18X CKP sensor connector disconnected.
  3. Disconnect the ICM connector.
  4. Test the 18X CKP sensor ground for an open.
  5. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 38

13

  1. Turn off the ignition switch.
  2. Leave the 18X CKP sensor connector disconnected.
  3. Disconnect the ignition ICM connector.
  4. Test the 18X CKP sensor feed for an open or a short to ground.
  5. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 41

14

  1. Leave the DMM connected.
  2. Turn off the ignition switch.
  3. Disconnect the ICM connector.
  4. Turn on the ignition switch.

Is the voltage near the specified value?

B+

Go to Step 15

Go to Step 16

15

Locate and repair the short between the 18X CKP sensor signal CKT and the following CKTs:

    • The 18X CKP sensor feed CKT
    • The battery positive CKT

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

16

  1. Turn off the ignition switch.
  2. Disconnect the ICM connector.
  3. Turn on the ignition switch.
  4. Test the 18X CKP signal CKT for the following condition(s):
  5. • An open.
    • A short to ground or sensor ground.
  6. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 38

17

  1. Turn off the ignition switch.
  2. Disconnect all of the fuel injector connectors.
  3. Turn on the ignition switch.
  4. Observe the J 34730-2C fuel injector test lamp when installed in each injector connector.

Does the injector test lamp illuminate in any of the injectors?

--

Go to Step 18

Go to Step 19

18

  1. Leave the fuel injector connectors disconnected.
  2. Turn off the ignition switch.
  3. Disconnect the PCM connector.
  4. Turn on the ignition switch.
  5. Observe the injector test lamp in the injector connectors.

Does the injector test lamp illuminate in any of the injectors?

--

Go to Step 43

Go to Step 46

19

  1. Leave the fuel injector connectors disconnected.
  2. Leave the injector test lamp installed in the injector connector.
  3. Observe the injector test lamp while cranking the engine (repeat for each injector).

Does the injector test lamp blink in each of the injectors?

--

Go to Step 24

Go to Step 20

20

Did the injector test lamp blink for any of the injectors?

--

Go to Step 21

Go to Step 22

21

  1. Turn off the ignition switch.
  2. Leave the injector connectors disconnected.
  3. Disconnect the PCM connector.
  4. Test for an open in the fuel injector control circuit(s) associated with the injector test lamp that did not blink.
  5. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 44

22

  1. Leave the fuel injector connectors disconnected.
  2. Turn on the ignition switch.
  3. Connect a test lamp to ground.
  4. Probe the ignition positive voltage feed circuit to each injector connector.

Does the test lamp illuminate?

--

Go to Step  44

Go to Step 23

23

Locate and repair the open ignition positive feed circuit to the fuel injectors. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

24

  1. Turn off the ignition switch.
  2. Disconnect a spark plug wire from the spark plug.
  3. Install a J 26792 spark tester in the end of the spark plug wire.
  4. Jumper the companion cylinder ignition wire to engine ground. The companion cylinder is the cylinder that shares the same ignition coil (i.e. 1/4, 2/5, 3/6).
  5. Crank the engine while observing the spark tester. Spark should be observed.
  6. Repeat the above test for each ignition wire, noting any cylinders that do not have spark.

Is spark available at all cylinders?

--

Go to Step 34

Go to Step 25

25

Is spark available at any cylinder?

--

Go to Step  30

Go to Step 26

26

  1. Turn off the ignition switch.
  2. Disconnect the 18X CKP sensor connector.
  3. Turn on the ignition switch.
  4. Connect the DMM between the CKP sync signal circuit and ground.

Is the voltage within the specified range?

6-8 V

Go to Step 27

Go to Step 28

27

  1. Inspect for faulty terminal connections at the 18X CKP sensor.
  2. If a problem is found, repair as necessary. Refer to Connector Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 41

28

  1. Turn off the ignition switch.
  2. Disconnect the ICM connector.
  3. Turn on the ignition switch.
  4. Test the CKP sync signal CKT or the 18X CKP sensor feed circuit for a short to voltage.
  5. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 29

29

  1. Turn off the ignition switch.
  2. Disconnect the ICM connector.
  3. Turn on the ignition switch.
  4. Test for the following circuit conditions:
  5. • The CKP sync signal circuit for a short to ground or sensor ground.
    • An open CKP sync signal circuit.
  6. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 38

30

  1. Visually/physically inspect the ignition coils and the ignition wires associated with the cylinders that did not have spark.
  2. Ensure that the ignition wires, boots, coils, and coil towers are free of cracks and carbon tracking.
  3. If a problem is found, replace the damaged ignition component(s). Refer to Ignition Coil Replacement and/or Spark Plug Wire Harness Replacement .

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 31

31

  1. Measure the ignition coil secondary resistance.
  2. If any resistance is outside the specified range, replace the malfunctioning ignition coil(s). Refer to Ignition Coil Replacement .

Was a problem found?

5K-8K ohms

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 32

32

  1. Measure the resistance of the ignition wires associated with the cylinders that did not have spark.
  2. Replace the ignition wire(s) that measure more than the specified value. Refer to Spark Plug Wire Harness Replacement .

Was a problem found?

600 ohms/ ft

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 33

33

  1. Remove the coil(s) associated with the non sparking cylinders. Refer to Ignition Coil Replacement .
  2. Connect a test lamp across the ignition module primary circuit (between the electronic ignition control module terminals) for the coil(s) associated with the cylinders which did not have spark.
  3. Observe the test lamp while cranking the engine.

Does the test lamp blink continuously while the engine is being cranked?

--

Go to Step 45

Go to Step 42

34

  1. Remove the spark plugs from all of the cylinders. Refer to Spark Plug Replacement .
  2. Visually/physically inspect the spark plug electrodes. Refer to Spark Plug Visual Diagnosis .
  3. Do the spark plugs have excessive fouling?

--

Go to Rough, Unstable, or Incorrect Idle and Stalling .

Go to Step 35

35

  1. Refer to Diagnostic Aids in order to test for the following conditions:
  2. • A short between the 18X CKP and CKP sync signal inputs to the ICM.
    • A short between the 18X and 3X reference signal inputs to the PCM.
    • A stuck throttle position (TP) sensor.
    • A skewed engine coolant temperature (ECT) sensor.
    • A skewed or unresponsive manifold absolute pressure (MAP) sensor.
  3. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 36

36

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

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 37

37

Repair an engine mechanical problem. Refer to Engine Noise Diagnosis in order to diagnose the following conditions:

    • Bent push rods
    • Malfunctioning 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

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

38

Test for faulty terminal connections at the ICM.

If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 42

39

Locate and repair the open in the ICM ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

40

Locate and repair the open in the ignition positive feed circuit to the ICM. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

41

Replace the 18X CKP sensor. Refer to Crankshaft Position Sensor Replacement .

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

42

Replace the ICM.

Refer to Ignition Control Module Replacement .

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

43

Locate and repair the short to ground in the fuel injector control circuit(s) associated with the injector test lamp(s) that stayed illuminated. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

44

Test for faulty terminal connections at the PCM.

If a problem is found, repair as necessary. Refer to Connector Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 46

45

Replace the ignition coil(s) associated with the cylinder(s) that did not have spark. Refer to Ignition Coil Replacement .

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--

46

Important: A replacement PCM must be reprogrammed. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Did you complete the repair?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--