GM Service Manual Online
For 1990-2009 cars only

Object Number: 65572  Size: MF
Handling ESD Sensitive Parts Notice
Engine Controls Components
Ignition Controls
OBD II Symbol Description Notice

Circuit Description

The Crankshaft Position (CKP) sensor sends a reference signal to the Vehicle Control Module (VCM). The CKP reference signal is used to determine crankshaft position and engine RPM. This information is used by the VCM in order to determine when to pulse the ignition coil and to control the ignition timing. This diagnostic will detect a low duty cycle from the crankshaft sensor. This is a type B DTC.

Conditions for Setting the DTC

    • The engine speed is less than 4000 RPM
    • The MAF is at least 5 g/s
    • The crank sensor duty cycle high reference to low reference ratio is greater than 0.6875

Action Taken When the DTC Sets

The VCM stores the DTC in History if the VCM detects an intermittent problem.

Conditions for Clearing the MIL/DTC

A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

Diagnostic Aids

A poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation may cause an intermittent.

Throroughly check any circuitry that is suspected of causing the intermittent complaint. Check for the following conditions:

    • Backed out terminals
    • Improper mating
    • Broken locks
    • Improperly formed or damaged terminals
    • Poor terminal to wiring connections or
    • Physical damage to the wiring harness

Refer to Intermittent Conditions .

Test Description

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

  1. This step determines if DTC P0338 is the result of a hard failure or an intermittent condition.

  2. This step determines if a voltage is available to the CKP through the VCM.

  3. If the feed circuit is shorted to ground, the test light will be ON. This step determines if the circuit is open or shorted to ground. If the circuit is OK, then the VCM connections or VCM is malfunctioning.

  4. This test checks the crank sensor, crank sensor signal circuit and the VCM.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing the DTCs, use the scan tool to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear Info function is used.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Does the engine start?

--

Go to Step 4

Go to Step 3

3

  1. Clear the DTCs.
  2. Crank the engine for 10 seconds.

Does DTC P0338 set?

--

Go to Step 4

Go to Engine Cranks but Does Not Run

4

  1. Start the engine.
  2. Observe the engine RPM on the scan tool.

Does the RPM fluctuate (up to twice the desired RPM)?

--

Go to Step 14

Go to Step 5

5

  1. Turn ON the ignition leaving the engine OFF.
  2. Disconnect the Crankshaft Position sensor electrical connector.
  3. With a test lamp connected to ground, probe cavity C of the Crankshaft Position sensor connector (engine side).

Is the test lamp ON?

--

Go to Step 6

Go to Step 8

6

Jumper the test lamp between cavities B and C of the Crankshaft Position sensor electrical connector.

Is the test lamp ON?

Go to Step 7

Go to Step 12

7

  1. Turn OFF the ignition.
  2. Install the gray jumpers from J 35616 connector test adapter kit.
  3. Allow the engine to run
  4. Use a DVM in order to measure the voltage on the 3X signal circuit.

Is the voltage between the specified value?

2-3V

Go to Step 16

Go to Step 9

8

  1. Turn OFF the ignition.
  2. Disconnect the VCM BLUE connector.
  3. With a test lamp connected to B+, again probe cavity C of Crankshaft Position sensor.

Is the test lamp OFF?

--

Go to Step 15

Go to Step 11

9

Check the Crankshaft Position sensor signal circuit for an open.

Was a problem found?

--

Go to Step 17

Go to Step 10

10

Check the Crankshaft Position sensor signal circuit for a short to ground.

Was a problem found?

--

Go to Step 17

Go to Step 13

11

Repair short to ground in Crankshaft Position sensor feed circuit. Refer to Wiring Repairs in Engine Electrical.

Is the repair complete?

--

Go to Step 19

--

12

Repair the open in the Crankshaft Position sensor ground circuit. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 19

--

13

Check for a poor connection at the Crankshaft Position sensor.

Was a problem found?

--

Go to Step 17

Go to Step 14

14

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

Is the replacement complete?

--

Go to Step 19

--

15

Check for an open in the Crankshaft Position sensor feed circuit.

Was a problem found?

--

Go to Step 17

Go to Step 16

16

Check for a poor connection at the VCM.

Was a problem found?

--

Go to Step 17

Go to Step 18

17

Repair the circuit as necessary. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 19

--

18

Replace the VCM.

Important:  When replacing the VCM, the new VCM will need to be programmed. Refer to VCM Replacement/Programming .

Is the action complete?

--

Go to Step 19

--

19

  1. Use the scan tool in order to select the DTC and the Clear Info.
  2. Start the Engine.
  3. Allow the engine to idle until the normal operating temperature is reached.
  4. Select the DTC and the Specific.
  5. Enter the DTC number which was set.
  6. Operate the vehicle within the conditions for setting this DTC as specified in the supporting text.

Does the scan tool indicate that this diagnostic ran and passed?

--

Go to Step 20

Go to Step 2

20

Use the scan tool in order to display the Capture Info and the Review Info.

Are there any DTCs displayed that have not been diagnosed?

--

Go to the applicable DTC table

System OK