Crankshaft Position Sensor on the Jeeps (4.0 & 2.5) reads a set of slots that is spinning on the flywheel. These slots cause the CKPS to send a pulse to the Power Control Module (ignition computer/brain box) indicating engine speed. Also the PKCM uses this pulse signal to set ignition timing and supplying the tachometer with the RPM that you see in the dash.
is the sensor located?
Sensor is located on the driver’s side of the engine, back of the block where the transmission joins the block. Bolted to the transmission bell housing with 2 bolts and has a long wiring harness/plug coming up by the fuel rails.
Will it trigger the check engine light if the sensor is faulty?
Yes it will trigger the “check engine” light. But most of the time when the Crankshaft sensor goes the engine is dead as a hammer. It will turn over but will not fire at all. Occasionally a CPS will cool down long enough to fire up again. Then you get you down the road a little bit and it leaves you stranded again when it gets hot and decides to quit.
Why does it fail?
Heat is the biggest issue for this sensor going bad.
How do you test a Crankshaft Position sensor to see if it’s bad?
You just need a Multi-meter for this test.
Set your meter to measure ohms (Ω) using the scale between 1K-10K. Place your leads across posts B & C of the CPS plug.
You should get a reading of open or no resistance. If you get a reading of low resistance, replace the sensor.
On all 2.5L & 4.0L engines (except YJ models that come with the 4.0/automatic combination) there are 2 bolts and the plug to deal with. Unplug the harness. Just take out those 2 bolts and pull the sensor out of the bell housing. For the 2.5L/automatic the sensor is help in place with 2 nuts instead of bolts. The YJ Wranglers that come with the 4.0/automatic, the sensor uses a single slotted hole to adjust the mounting depth. When purchasing a new sensor for the 4.0/auto YJ there will be paper spacer attached to the end of the sensor that gets inserted into the bell-housing. This spacer sets the correct depth to be installed. Simply drop the sensor in until the paper spacer bottoms out in the hole, then tighten the bolt. When the engine turns over it rips the paper off the sensor, don't worry .. it's not gonna hurt anything having that tiny paper shard in there. As for the all the others that do not use the paper spacer, simply drop it in until the sensor body is flush to the bell housing, tighten the bolt and you are done.
Replacing the sensor in Wranglers isn’t too bad. Cherokees are a bit more troublesome to access. My Wrangler I can get it from the bottom or top. Cherokees because of having more goodies in the way, they tend to be a bit easier to get from the bottom. Use an extension or two and reach over the bell housing of the transmission to reach the bolts.
NOTE: When you go to re-install the CKPS don’t get the bright idea of putting a bolt through the sensor and then drop the sensor into the hole it goes in. Why you ask? Simple .. it would be way too easy for that little bolt to be dropped and fall right into the little hole where the Crankshaft Position Sensor goes. If that happens you will have to pull the transmission back to get the bolts out, NOT FUN! Put the CKPS into the hole first, fully seating it into place. THEN put the bolts in. The hole is now plugged so nothing can fall in.