GM Service Manual Online
For 1990-2009 cars only

Refer to Engine Controls Schematics

Crankshaft and Camshaft Position Sensors


Object Number: 589889  Size: FS
UAWJB, Automatic Transaxle, ICM, HO2S1 and HO2S2
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Instrument Panel, Gages, and Console Component Views
Instrument Cluster Circuit Description
Fuel Tank Input/Output (L36 Only)
Power and Grounds
OBD II Symbol Description Notice
for a wiring diagram.

Circuit Description

The 18X reference signal is produced by the ignition control module (ICM). The ICM calculates the 18X reference signal by filtering the crankshaft position (CKP) sensor 18X pulses when the engine is running and CKP sync pulses are also being received. The powertrain control module (PCM) uses the 18X reference signal to calculate engine RPM and crankshaft position at engine speeds below 1200 RPM. The PCM constantly monitors the number of pulses on the 18X Reference circuit and compares the number of 18X reference pulses to the number of 3X reference pulses and CAM signal pulses being received. If the PCM receives an incorrect number of pulses on the 18X Reference circuit, the PCM will use the 3X reference signal circuit for fuel and ignition control. The engine will continue to start and run using the 3X reference and CAM signals only. DTC P0336 will set.

Conditions for Running the DTC

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

Conditions for Setting the DTC

    • The ratio of 18X reference pulses to 3X reference pulses received by the PCM does not equal 6 to 1.
    • The ratio of 3X reference pulses to CAM signal pulses received by the PCM equals 6 to 1.
    • The conditions are present for more than 10 seconds.

Action Taken When the DTC Sets

    • The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
    • The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

Conditions for Clearing the MIL/DTC

    • The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.
    • The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
    • The DTC can be cleared by using a scan tool.

Diagnostic Aids

An intermittent may be caused by:

    •  A poor connection
    •  Rubbed through wire insulation
    •  A broken wire inside the insulation

Inspect for the following conditions:

    • Misrouted wiring harness -- Inspect the ICM harness to ensure that it is not routed near secondary ignition components.
    • Malfunctioning ignition coil -- Remove the ignition coils and inspect the ignition control module and coils for cracks, carbon tracking, or other signs that indicate that the coil secondary circuit is arcing to the ICM or ICM wiring harness. Refer to Ignition Coil Replacement .
    • Secondary ignition wires arcing to wiring harness -- Inspect secondary ignition wires for carbon tracking or other signs of damage.

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: :  Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

    • Loose terminal connection
       -  Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.
       -  Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.
    • Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.
    •  Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

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 Powertrain On-Board (OBD) system check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

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 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 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 and Connector Repairs .

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 and Connector Repairs .

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 and Connector Repairs .

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/Programming 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/Type

System OK