If the CKP sensor (crank position sensor) ) goes bad on your engine which is located up front by the oil filter, there has to be a way to keep the engine running so it can get you home. This is a magnetic switch that picks up an impulse from serrations that pass the switch in the edge of the flywheel. This switch is also a target for metallic fuzz that circulates in the engine oil just like what you find on the drain plugs when doing a service.
It's purpose is to send data to the ECM about the engine speed which interprets this and is used for proper data output for various purposes.
You will notice slight hesitation just off idle and poor running as well as poor gas mileage.
The bike will go into "limp home mode" if this happens while riding and it does not always set a code. It has also been responsible for a no spark/no start condition when they fail.
That means you will be able to get home running even if it is at a much reduced performance state.
The ECM is smart enough to look elsewhere for RPM data like the M.A.P. sensor which tells the ECM the state of intake, which can loosely be used for firing timing.
As with all sensors, age can effect their performance and this may be a gradual decrease until one day you realize that it just isn't running as good as it use to and you notice a hesitation off idle.
This sensor is the one that is in the way when you change the oil filter.
To test this sensor...
The CKP sensor has a B+ power supply, a ground, and a signal circuit.
As the crankshaft rotates, the wheel teeth interrupt a magnetic field produced by a magnet within the sensor. The sensor's internal circuitry detects this and produces a signal which the ECM reads. The ECM uses this signal to accurately measure crankshaft velocity which is a variable used in order to detect misfire, spark and, fueling.
Looking at your service manual find the wire that goes to the B+ (battery) Measure from this wire to ground for the DC supply voltage. Measurement should be taken on the sensor side of the connector. Ground connection as well.
Do this test at rest and also with the engine spinning. A loose connection could break as the motor shakes. There was an upgrade to the sensor in January 2004 available here...
Crank Position Sensor Change - Harley Davidson Community
If you have voltage present with the key on and with the engine spinning move the positive meter lead to the Signal wire. This is usually marked R for Red . With the engine spinning you should see a voltage signal on that wire.
You should measure the signal at the sensor connector and the ECM to verify it is reaching the ECM.
Linear Mode
