P0338

Schematic:

The crankshaft position (CKP) sensor produces an AC voltage of different amplitude and frequency depending on the velocity of the crankshaft. The CKP sensor works in conjunction with a 58 tooth reluctor wheel on the crankshaft. Each tooth is spaced six degrees apart with one span having a 12 degree space that is uncut. This uncut portion creates a pattern that enables the ECM to determine top dead center for cylinder # 1 and its mating cylinder, cylinder # 4. The camshaft position (CMP) sensor is then used to determine when cylinder # 1 is on its compression stroke. With both CKP sensor and CMP sensor inputs, the ECM can properly synchronize ignition timing, fuel delivery and spark knock control. The ECM uses a pull-up voltage of 2.5 volts on each CKP sensor wire used for the reduction of noise interference from electromagnetic generating devices. DTC P0338 will set if the ECM detects more CKP sensor signal pulses within a certain number of crankshaft revolutions when the engine is cranking or running. This indicates that the CKP sensor circuit is experiencing electromagnetic interference, the sensor frequency characteristics have changed or a short to voltage in the wiring may exist.

DTC PARAMETERS
DTC P0338 will set if the ECM detects more pulses per crankshaft revolution then expected (more than 58 pulses) from the CKP sensor A/C voltage signal when:
^ Condition exists for eight consecutive crankshaft revolutions in which the same number of missing pulses (+/-1 pulse) are being detected each crankshaft revolution
^ A valid CMP sensor signal is being received
^ Engine is cranking or running

DTC P0338 diagnostic runs continuously with engine running or cranking.

P0338 is a type B DTC.

DIAGNOSTIC AIDS

NOTE: A short to voltage on circuit 5039 will NOT affect engine operation. The engine will run if this condition occurs. A short to voltage on circuit 5024 will affect engine operation. The engine will stall below 2500 rpm if this condition occurs.

Make sure circuit 5039 and 5024 each has 2.5 volts from the ECM. If the voltage is greater than 4 volts on either circuit, check for a short to voltage. An intermittent short to voltage will cause frequency fluctuations and may set this DTC.

Make sure the battery cables are clear of the CKP sensor wiring, which may cause electromagnetic interference.

If there are 2.5 volts on each CKP sensor circuit and the wiring is clear of the battery cables, replace the CKP sensor.