One of the common issues older Jeeps sometimes have is a bad or faulty crankshaft position sensor (CPS). A bad crankshaft position sensor can literally stop your Jeep. This article will discuss what crankshaft position sensors are, how they work, how to determine if they are bad, and most importantly, how to change the Jeep crankshaft position sensor (CPS). I have changed crankshaft position sensors on Jeep XJ, TJ, and ZJ’s.
Changing a Jeep’s crankshaft position sensor is a bit of challenging DIY task, however, it is certainly a job that a Jeep DIY mechanic can do in about hour or so. You will need some basic tools such as a ratcheting wrench, sockets, and several socket extensions, as well as a flashlight, shop towels, string, a pickup tool, and a great deal of patience to complete this job.
What is a Crankshaft Position Sensor (CPS)?
Your Jeep’s crankshaft position sensor is a sensor that identifies and determines that the engine is turning. While not a unique part to Jeeps, the crankshaft position sensor is known to act up or fail more often in Jeeps for some reason – some people believe excessive heat plays a role.
How Does a Crankshaft Position Sensor Work?
The crankshaft position sensor is a magnet that reacts to various holes cut into the flywheel in your Jeep’s bellhousing. The signals it receives are converted into signals sent to the Jeep’s PCM (the Jeep’s computer) and appropriate adjustments are made to fuel mixture and spark timing based on those signals from the crankshaft position sensor. Sometimes, a bad crankshaft position sensor can allow your Jeep to crank, but not turn over and start.
How Do I know if My Jeep’s Crankshaft Position Sensor is Going Bad?
Bad or failing crankshaft position sensor symptoms can vary, but here are a few to look for on your Jeep:
- Difficult starting or no starting
- Acceleration, stalling, and “sputtering” problems
- Rough idling
- Reduced gas mileage
- Engine misfires
- Check engine light
If you have confirmed fuel pressure to the fuel rail and spark at the plugs, distributor or coil(s) (topics to be covered in a future article), then the Jeep’s crankshaft position sensor is probably the issue with the Jeep.
Where is My Jeep’s Crankshaft Position Sensor Located?
In Jeeps, the crankshaft position sensor is located at the 11:00 o’clock position on the transmission bellhousing when you are looking toward the front of the vehicle—it’s on the driver’s side. This location is what makes the job so challenging. That said, the job is doable for a DIY mechanic, but you will have to be smart, prepared, and very, very patient.
How Do I Change My Jeep’s Crankshaft Position Sensor?
Changing your Jeep’s crankshaft position sensor will probably take you more than an hour the first time you do it, with the practice I have had on four Jeeps, I know it can be done in about 30-40 minutes.
Here’s what you will need:
- Ratcheting wrench and socket set (need 11mm deep and shallow socket)
- Several socket extensions to make an 18-24” long extension
- Universal joint socket adaptor
- Power wrench
- Shop towels
- Pickup tool with claws
- Magnetic pickup tool
- String (3-4 feet long)
- Disposable gloves
- Eye protection
- PB Blaster
If your Jeep isn’t lifted, you may want to consider raising the Jeep:
Here’s what to do to remove the old crankshaft position sensor:
- You will get dirty doing this job, so dress accordingly
- Put the Jeep up if necessary using the ramps or a jack and jack stands—either way, don’t forget the wheel chocks
- Disconnect the negative battery terminal
- Get under the Jeep from the driver’s side and use the flashlight to find the crankshaft position sensor on the transmission bellhousing, again it is at the 11:00 o’clock position
- Consider hitting the bolt or bolts with some liquid penetrating oil spray like PB Blaster
- Setup your extensions to reach up to the crankshaft position sensor, you will need between 18 and 24” to reach the bolt(s)
- The Jeep Wrangler TJ and the Jeep Grand Cherokee ZJ both have one retaining bolt, while the Jeep Cherokee XJ has two retaining bolts for twice the fun! I believe they are all 11mm bolts
- Crack the bolt or bolts loose and start to remove it/them. They aren’t very long, maybe an inch. When you get close to the bolt or bolts coming out consider using the magnetic pickup tools to grab them as opposed to letting them drop
- When the bolt or bolts are out, go to the engine bay and reach in, if you can (very tight space), and gently tug the sensor out by its cord. On the Jeep Grand Cherokee ZJ, be sure to retrieve the protective wire shield
- Once the sensor comes out you can disconnect it. In the Jeep Wrangler TJ and the Jeep Cherokee XJ, the plug is connected on the driver’s side toward the back of the intake manifold and valve cover. In the Jeep Grand Cherokee ZJ, the cord goes over the bellhousing behind the engine, and the connector is down much lower by the engine block on the passenger side of the Jeep
That’s removal—the easy part.
Here’s what to do to replace the new crankshaft position sensor:
- Muster up a great deal of patience, this is a challenging, but not impossible job
- Tie a long string near the crankshaft position sensor connector. This is very important for the Jeep Grand Cherokee ZJ installations since you will need to pull and wrap around the back of the engine over the transmission bellhousing. It is also helpful in the Jeep Cherokee XJ and Jeep Wrangler TJ installations. Once successfully fished through (I use a pickup tool with claws to help with this), tie the other end to something to hold it in place, but allow some play so you can do the next step
- Now it is time to do the first challenge, the positioning of the new crankshaft position sensor. The issue is the space is very tight and you will probably have to work blindly and by feel. On the Jeep Cherokee XJ it pays to enlist help from a skinny armed, long fingered helper (teenage daughters can help here) working from above, while you look from underneath and direct them how to move and adjust to get the sensor into the hole on the transmission bellhousing. The Jeep Wrangler TJ and Jeep Grand Cherokee ZJ have more space and I can work my hand and arm in (In fact, the Jeep Wrangler TJ is the easiest of the bunch). I then feel for the hole in the transmission bellhousing and slide the sensor in—it takes a few tries. I have recently figured out that on the Jeep Grand Cherokee ZJ, I can reach up from the bottom with my arm in front of the transmission bellhousing and be able to look from the back of the transmission bellhousing at the same time to get the sensor in the hole. I discovered this because I needed a way to position the protective wire shield into place
- Once the crankshaft position sensor is seated in the bell housing hole, carefully adjust it with the extensions from underneath. On the Jeep Grand Cherokee ZJ, be sure to position the wire shield as well
- The final challenge is to carefully get the retaining bolt or bolts into place. Here is the trick—use a 1×1” square of shop towel to securely hold the bolt in the socket on the end of the long extensions and carefully slide the bolt into place and start to fasten it. I do by hand with the socket and extensions not attached to the ratcheting wrench. I do this to have more control and avoid stripping the bolt in. Once the bolt is started, I switch to the wrench and finish the job. One Word of Caution: Don’t drop a bolt into the sensor hole on the transmission bellhousing. Granted, this shouldn’t be possible since the sensor should already be in the hole, but I would be remiss, not mentioning it
- If you are doing the Jeep Cherokee XJ, alternate tightening between the bolts until done
- Tighten the bolt(s) to very “finger” snug – by which I mean as tight as your fingers can turn the wrench, not your wrist or whole arm. You just won’t be able to do an effective torque wrench reading given the space and position- so don’t bother
- Once the bolt(s) is in, the hard part of this job is over
- Go up top to the engine bay and make the connection of the sensor to the wiring harness- it should make a click sound
- Reconnect the negative battery terminal and fire up your Jeep
- If you raised the Jeep, safely return it to the ground
Now go out and enjoy your Jeep!
Here are respective crankshaft position sensors for certain Jeeps:
- Jeep Cherokee XJ
- Jeep Wrangler TJ (May also apply to later Jeep XJ’s 1997 and later- please be sure to confirm fitment)
- Jeep Grand Cherokee ZJ