DTC P0338 Crankshaft Position (CKP) Sensor Circuit High Duty Cycle. Chevrolet Astro

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2000 🢒 Astro - 2WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 DTC P0338 Crankshaft Position (CKP) Sensor Circuit High Duty Cycle

Engine Controls Components
Ignition System Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The crankshaft position (CKP) sensor is a sensor designed to detect changes in a magnetic field. The control module supplies the CKP sensor a signal and ground circuits. Ignition voltage is supplied to the sensor by an independent circuit. The CKP sensor produces a magnetic field whenever the ignition is ON. The CKP sensor is mounted near a reluctor wheel that is attached to the crankshaft. When the crankshaft rotates, when the engine is cranking or running, the toothed reluctor wheel changes the magnetic field. The CKP sensor converts each change in the magnetic field into a PULSE. The number of teeth on the reluctor wheel determines how many pulses the CKP sensor detects per crankshaft rotation. The CKP sensor signal is used in order to determine the engine speed, the crankshaft position, and to detect misfire.

If the CKP frequency is more than expected by the VCM, this DTC will be set.

Conditions for Running the DTC

•	The engine speed is more than 4000 RPM.

•	The mass air flow (MAF) is 5 g/s or more.

Conditions for Setting the DTC

The CKP sensor duty cycle is more than a calibrated value.

Action Taken When the DTC Sets

•	The control module stores the DTC in history after the first failure but will not illuminate the malfunction indicator lamp (MIL).

•	The control module records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

•	A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles.

•	A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle.

•	Use the scan tool Clear Information function.

Diagnostic Aids

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

•	Inspect for the following conditions:

-	A chipped or damaged reluctor wheel

-	An incorrect reluctor wheel

-	The incorrect alignment of the CKP sensor to reluctor wheel

-	Excessive crankshaft end play

-	Electromagnetic interference

•	Test for intermittents. Refer to Symptoms .

An intermittent may be caused by any of the following conditions:

•	A poor connection

•	Rubbed through wire insulation

•	A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

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

It is very difficult to start an engine with a crank sensor high duty cycle failure. A running engine however may not be adversely affected by a high duty cycle failure.

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

This test checks the crank sensor for a duty cycle that is too high.

Step	Action	Values	Yes	No
1	Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?	--	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 the DTCs. Crank the engine for 10 seconds. Does DTC P0338 set?	--	Go to Step 4	Go to Engine Cranks but Does Not Run
4	Turn OFF the ignition. Disconnect the CKP sensor harness connector. Install the gray jumpers from the J 35616 connector test adapter kit between the engine harness connector and the CKP sensor. Important: The positive lead from the DMM must be connected to the CKP 3X signal circuit. Connect a digital multimeter (DMM) set to the duty cycle position between the CKP sensor 3x signal circuit and the CKP sensor ground circuit. Select the AC scale and press the Hz button twice in order to display the percent duty cycle Crank the engine. Is the duty cycle more than the specified value?	60%	Go to Step 5	Go to Step 8
5	Inspect the CKP sensor and the reluctor wheel for damage. Refer to Diagnostic Aids. Did you find a problem?	--	Go to Step 6	Go to Step 7
6	Replace the CKP sensor and/or the crankshaft reluctor wheel. Refer to Crankshaft Position Sensor Reluctor Ring Replacement in Engine Mechanical, and to Crankshaft Position Sensor Replacement . Perform the CKP System Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn . Is the action complete?	--	Go to Step 10	--
7	Important: Inspect the CKP sensor mounting surface in order to insure the surface is clean and free of debris. Replace the CKP sensor. Refer to Crankshaft Position Sensor Replacement . Perform the CKP System Variation Learn Procedure. Refer to Crankshaft Position System Variation Learn . Is the action complete?	--	Go to Step 10	--
8	Using the scan tool, clear the DTCs. Start the engine. Allow the engine to idle until the engine reaches a normal operating temperature. Select the DTC and the Specific DTC functions. Enter the DTC number that was set. Operate the vehicle within the Conditions for Setting the DTC until the scan tool indicates the diagnostic Ran. Does the scan tool indicate the diagnostic Passed?	--	Go to Step 11	Go to Step 9
9	Important: The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete?	--	Go to Step 10	--
10	Using the scan tool, clear the DTCs. Start the engine. Allow the engine to idle until the engine reaches a normal operating temperature. Select the DTC and the Specific DTC functions. Enter the DTC number that was set. Operate the vehicle within the Conditions for Setting the DTC until the scan tool indicates the diagnostic Ran. Does the scan tool indicate the diagnostic Passed?	--	Go to Step 11	Go to Step 2
11	Does the scan tool display any additional undiagnosed DTCs?	--	Go to the applicable DTC table	System OK