GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2005 🢒 LaCrosse 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Crankshaft Position Sensor System Diagnosis

Circuit Description

The ignition control module (ICM) monitors the crankshaft position (CKP) sensor sync signal when the engine is cranking. The CKP sync signal is passed from the CKP sensor to the ICM on the CKP sensor 2 signal circuit. The CKP sync signal is used to determine the correct cylinder pair and initiate the ignition coil firing sequence. The 18X reference pulses are passed from the CKP sensor to the ICM on the CKP sensor 1 signal circuit. The 18X reference pulses are used for fuel injection and ignition control. After the ICM receives both signals, the ICM passes the 18X and 3X reference signals to the powertrain control module (PCM). The camshaft position sensor and the CKP sensor share a 12-volt reference and a low reference circuit. The CKP sensor consists of the following circuits:

    • A 12-volt reference circuit
    • A low reference circuit
    • A CKP sensor 1 signal circuit
    • A CKP sensor 2 signal circuit

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Attempt to start the engine.

Does the engine start and run?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3
  1. Crank the engine.
  2. Observe the Engine Speed parameter with a scan tool.

Does the scan tool display engine RPM?

--

Go to Step 12

Go to Step 4

4
  1. Turn OFF the ignition.
  2. Disconnect the ignition control module (ICM).
  3. Turn ON the ignition.
  4. Measure the voltage from the ignition 1 voltage circuit of the ICM to a good ground with a DMM. Refer to Circuit Testing .

Is the voltage equal to the specified value?

B+

Go to Step 5

Go to Step 14

5

Test the ignition 1 voltage circuit of the ICM for high resistance. Refer to Circuit Testing and Wiring Repairs .

Is the resistance greater than the specified value?

1 ohms

Go to Step 26

Go to Step 6

6

Measure the voltage between the ignition 1 voltage circuit and the ground circuit of the ICM with a DMM. Refer to Circuit Testing .

Is the voltage within the specified value?

B+

Go to Step 7

Go to Step 15

7
  1. Turn OFF the ignition.
  2. Connect the ICM.
  3. Disconnect the crankshaft position (CKP) sensor.
  4. Turn ON the ignition.
  5. Measure the voltage from the 12-volt reference circuit of the CKP sensor to a good ground with a DMM. Refer to Circuit Testing .

Is the difference between the measured voltage and the system voltage more than the specified value?

1 V

Go to Step 16

Go to Step 8

8

Measure the voltage between the 12-volt reference circuit and the low reference circuit of the CKP sensor with a DMM. Refer to Circuit Testing .

Is the difference between the measured voltage and the system voltage more than the specified value?

1 V

Go to Step 17

Go to Step 9

9

Test for high resistance in the 12-volt reference circuit and the low reference circuit of the CKP sensor. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 10

10

Measure the voltage between the CKP sensor 1 signal circuit and the low reference circuit of the CKP sensor with a DMM. Refer to Circuit Testing .

Is the voltage within the specified range?

4-8 V

Go to Step 23

Go to Step 11

11

Is the voltage more than the specified range?

4-8 V

Go to Step 18

Go to Step 19

12
  1. Disconnect the CKP sensor.
  2. Turn ON the ignition.
  3. Measure the voltage between the CKP sensor 2 signal circuit and the low reference circuit of the CKP sensor with a DMM. Refer to Circuit Testing .

Is the voltage within the specified range?

4-8 V

Go to Step 22

Go to Step 13

13

Is the voltage more than the specified range?

4-8 V

Go to Step 20

Go to Step 21

14

Test for an open or short to ground in the ignition 1 voltage circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 25

15

Repair the open or high resistance in the ground circuit. Refer to Circuit Testing and Wiring Repairs .

Did you complete the repair?

--

Go to Step 31

--

16

Test the 12-volt reference circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 25

17

Test the low reference circuit for an open and for high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 25

18

Test the CKP sensor 1 signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 25

19

Test the CKP sensor 1 signal circuit for an open and for a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 25

20

Test the CKP sensor 2 signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 25

21

Test the CKP sensor 2 signal circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 25

22

Test the CKP sensor 2 signal circuit for high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 24

23

Test the CKP sensor 1 signal circuit for high resistance, and for the CKP sensor signal 1 circuit shorted to the CKP sensor signal 2 circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 24

24

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 .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 27

25

Test for shorted terminals and for a poor connection at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 30

26

Repair the high resistance in the ignition 1 voltage circuit. Refer to Wiring Repairs .

Did you complete the repair?

--

Go to Step 31

--

27
  1. Remove the CKP sensor. Refer to Crankshaft Position Sensor Replacement .
  2. Visually inspect the CKP sensor for the following conditions:
    3. • Physical damage
    • Excessive play or looseness
    • Improper installation
    • Foreign material passing between the CKP sensor and the reluctor wheel
    • Excessive air gap between the CKP sensor and the reluctor wheel
    • Electromagnetic interference (EMI) in the CKP sensor circuits

Did you find and correct the condition?

--

Go to Step 31

Go to Step 28

28

Inspect the crankshaft reluctor wheel for the following conditions:

    • Physical damage
    • Excessive end play or looseness
    • Improper installation

Refer to Crankshaft and Bearing Cleaning and Inspection .

Did you find and correct the condition?

--

Go to Step 31

Go to Step 29

29

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

Did you complete the replacement?

--

Go to Step 31

--

30

Replace the ICM. Refer to Ignition Control Module Replacement .

Did you complete the replacement?

--

Go to Step 31

--

31
  1. Turn the ignition OFF for 30  seconds.
  2. Start the engine and operate the vehicle.
  3. Observe the vehicle performance and driveability.

Does the vehicle operate normally?

--

System OK

Go to Step 2