GM Service Manual Online
For 1990-2009 cars only

Object Number: 33715  Size: MF
Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts 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 following conditions will set the DTC:

    • The engine speed is less than 4000 RPM
    • The MAF is at least 5 g/s
    • The crank sensor duty cycle is greater than 50% (or the ratio High Ref to Low Ref is greater than 5.66)

Action Taken When the DTC Sets

The VCM will turn ON the MIL after 2 consecutive driving cycles with the fault active.

Conditions for Clearing the MIL/DTC

The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.

Diagnostic Aids

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

Thoroughly check any circuitry, that is suspected of causing the intermittent complaint for the following conditions:

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

Inspect the face of the CKP sensor for metal shavings. This could result in an intermittent DTC P0339.

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. Determines if 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 faulty.

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

Step

Action

Value(s)

Yes

No

1

Important:  Before clearing DTCs, use the scan tool in order to record the freeze frame and the failure records for reference because the Clear Info function will lose the data.

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

Clear DTCs crank the engine for 10 seconds.

Does DTC P0338 set?

--

Go to Step 4

Go to Engine Cranks but Does Not Run

4

Start the engine, observe the engine RPM on the scan tool.

Does the RPM fluctuate (up to twice 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 A 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 engine to run
  4. Using a DVM, measure voltage on the 4X signal circuit.

Is the voltage between the specified value?

2-3 V

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 faulty 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 Sensor Replacement .

Is the action 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 faulty 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:  If the VCM is faulty, reprogram the VCM. Refer to VCM Replacement/Programming .

Is the action complete?

--

Go to Step 19

--

19

  1. Using the scan tool, select the DTC and the Clear Info.
  2. Start the Engine.
  3. Idle at the normal operating temperature.
  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

Using the scan tool, select the Capture Info and the Review Info.

Are any DTCs displayed that have not been diagnosed?

--

Go to The Applicable DTC Table

System OK