GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The crankshaft position (CKP) sensor is a 24X sensor. It provides 24 digital ON/OFF signals to the powertrain control module (PCM) per revolution of the crankshaft. This information is used by the PCM for ignition timing, fuel injector timing, misfire diagnostics, and tachometer display. The PCM supplies 12 volts to the sensor on the 12-volt reference circuit, and provides a ground on the low reference circuit. The CKP sensor provides signals to the PCM on the medium resolution engine speed signal circuit.

Diagnostic Aids

A faulty CKP sensor, CMP sensor, or a short to ground on either 12-volt reference circuit may cause the CKP signal to be lost, preventing the engine from running.

Test Description

The number below refers to the step number on the diagnostic table.

  1. Any change in RPM verifies that the controller is able to receive a signal.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

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

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Crank the engine.

Does the engine start and run?

--

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3

  1. Turn ON the ignition, with the engine OFF.
  2. Raise the vehicle. Refer to Lifting and Jacking the Vehicle.
  3. Test for an intermittent and for a poor connection at the crankshaft position (CKP) sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 4

4

  1. Disconnect the CKP sensor.
  2. Measure the voltage from the 12-volt reference circuit of the CKP sensor to a good ground with a DMM.

Is the voltage measured within 1 volt of the specified value?

B+

Go to Step 7

Go to Step 5

5

  1. Observe the DMM that is still connected between the 12-volt reference circuit of the CKP sensor and a good ground.
  2. Disconnect the camshaft position (CMP) sensor.

Does the voltage change?

--

Go to Step 19

Go to Step 6

6

Measure the voltage from the 12-volt reference circuit of the CMP sensor to a good ground with a DMM.

Is the voltage measured within 1 volt of the specified value?

B+

Go to Step 12

Go to Step 11

7

Measure the voltage from the 12-volt reference circuit to the low reference circuit of the CKP sensor with a DMM.

Is the voltage measured within 1 volt of the specified value?

B+

Go to Step 8

Go to Step 13

8

  1. Connect a test lamp to a battery positive voltage source.
  2. Probe the medium resolution engine speed signal circuit with the test lamp at the harness connector.

Does the test lamp illuminate?

--

Go to Step 14

Go to Step 9

9

  1. Tap the medium resolution engine speed signal circuit with the test lamp repeatedly at the harness connector.
  2. Observe the 24X Crank Sensor parameter with the scan tool.

Does the RPM change?

--

Go to Step 10

Go to Step 15

10

  1. Jumper the low reference circuit and the 12-volt reference circuit of the CKP sensor to the CKP harness connector with the J 35616 Terminal Test Kit. Refer to Circuit Testing.
  2. Measure the D.C. duty cycle from the medium resolution engine speed signal terminal at the CKP sensor to a good ground with a DMM. Refer to Circuit Testing.
  3. Crank the engine.

Does the DMM display the specified value?

OL

Go to Step 16

Go to Testing for Intermittent Conditions and Poor Connections

11

Test the 12-volt reference circuit of the CKP sensor and the CMP sensor for a short to ground. Refer to Circuit Testing.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 21

12

Test the 12-volt reference circuit of the CKP sensor for an open. Refer to Circuit Testing.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 18

13

Test the low reference circuit of the CKP sensor for an open. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 18

14

Test the medium resolution engine speed signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 21

15

Test the medium resolution engine speed signal circuit for an open or for a short to voltage. Refer to Circuit Testing and Wiring Repairs.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 18

16

  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 in the CKP sensor circuits

Did you find and correct the condition?

--

Go to Step 22

Go to Step 17

17

Inspect the reluctor wheel for the following conditions:

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

Did you find and correct the condition?

--

Go to Step 22

Go to Step 20

18

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.

Did you find and correct the condition?

--

Go to Step 22

Go to Step 21

19

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

Did you complete the replacement?

--

Go to Step 22

--

20

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

Did you complete the replacement?

--

Go to Step 22

--

21

Replace the PCM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 22

--

22

  1. Lower the vehicle.
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine.
  5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 23

23

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK