GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The crankshaft position (CKP) sensor is connected directly to the ignition control (IC) module. The CKP sensor consists of the following circuits:

    • The 10-volt reference circuit
    • The low reference circuit
    • The CKP sensor 1 signal circuit
    • The CKP sensor 2 signal circuit

The CKP sensor shares power supply and low reference circuits with the camshaft position (CMP) sensor.

Conditions for Running the DTC

The engine is running, and 3X reference pulses are being received.

Conditions for Setting the DTC

The 18X reference pulses are not received in 1 engine cycle, at 720 degrees of crankshaft rotation.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Inspect for the following conditions:

    • Incorrect harness routing near secondary ignition components.
    • Faulty ignition coil--Remove the ignition coils and inspect the ignition control module and coils for cracks, for carbon tracking, or for other signs that indicate that the coil secondary circuit is arcing to the ICM or to the ICM wiring harness. Refer to Ignition Coil Replacement .
    • Secondary ignition wires arcing to wiring harness--Inspect the secondary ignition wires for carbon tracking or for other signs of damage.
    • Poor Connections--Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

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 - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Attempt to start the engine.

Does the engine start and run?

--

Go to Step 3

Go to Step 8

3

Observe the 18X Crank Sensor parameter with the scan tool.

Does the 18X Crank Sensor parameter change with engine speed?

--

Go to Step 4

Go to Step 5

4

  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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.

Does the DTC fail this ignition?

--

Go to Step 5

Go to Testing for Intermittent Conditions and Poor Connections

5

  1. Turn OFF the ignition.
  2. Disconnect the ignition control module (ICM).
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a test lamp to a good ground.
  5. Probe the 18X reference medium resolution engine speed signal circuit at the ICM connector with the test lamp.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 6

6

  1. Connect the test lamp to battery voltage.
  2. Probe the 18X reference medium resolution engine speed signal circuit at the ICM connector with the test lamp.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 7

7

  1. Observe the 18X Crank Sensor parameter with the scan tool.
  2. Probe the 18X reference medium resolution engine speed signal circuit repeatedly at the ICM connector with the test lamp.

Does the 18X Crank Sensor RPM change?

--

Go to Step 13

Go to Step 11

8

  1. Disconnect the crankshaft position (CKP) sensor.
  2. Turn ON the ignition, with the engine OFF.
  3. Measure the voltage from the CKP sync signal circuit to a good ground with a DMM.

Is the voltage within the specified range?

4-8 V

Go to Step 14

Go to Step 12

9

Test the 18X reference medium resolution engine speed signal circuit between the ICM and the powertrain control module (PCM) for a short to ground. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 19

10

Test the 18X reference medium resolution engine speed signal circuit between the ICM and the PCM for a short to voltage. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 19

11

Test the 18X reference medium resolution engine speed signal circuit between the ICM and the PCM for an open. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 16

12

Test the CKP sync signal circuit for an open. Refer to Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 15

13

Inspect for the following conditions:

    • Incorrect harness routing near secondary ignition components
    • The ignition coil arcing to the wiring harness or to the ICM
    • The ignition coils for cracks, carbon tracking, or other signs of damage--Refer to Ignition Coil Replacement .
    • Spark plug wires arcing--Refer to Spark Plug Wire Replacement .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 15

14

Test for an intermittent or for poor connections at the CKP sensor. Refer to Testing for Intermittent Conditions and Poor Connections .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 17

15

Test for an intermittent or for poor connections at the ICM. Refer to Testing for Intermittent Conditions and Poor Connections .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 18

16

Test for poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections .

Did you find and correct the condition?

--

Go to Step 20

Go to Step 19

17

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

Did you complete the replacement?

--

Go to Step 20

--

18

Replace the ICM. Refer to Ignition Control Module Replacement .

Did you complete the replacement?

--

Go to Step 20

--

19

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

Did you complete the replacement?

--

Go to Step 20

--

20

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. 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 21

21

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK