I just swapped out a cracked flex plate this weekend, got everything back together and the Jeep just turns over and wont start. My first thought was the Crank Positioning Sensor so I pulled it out to test and I just wanted a sanity check to make sure I'm testing the correct points before I spend the money on a Mopar replacement.

Here is my connector and I believe I am supposed to be testing resistance on points 2 and 3.


And when testing those points here is my result

Am I correct in assuming this sensor is bad?

Thanks in advance!

 

Did you compare the two flexplates when you had them out? Apparently theres some out thwre woth the timing gaps are 30 or 40 degrees off causing all kinds of issues.

 

Yep, I made sure they matched up. I saw no difference between the old and the new.

 

Yes, the plate for the AW4 may be different from the plate for the 42re. You can check part numbers to be sure.

IDK what the resistance value is supposed to be, but you've got the right terminals.
#1 - sensor signal
#2 - sensor ground
#3 - 5v supply
When installed with key on, back probe terminal #1and a ground with an analog voltmeter and turn the crank by hand with a breaker bar and the signal voltage should go from 5v to zero every time it passes over a window in the plate.

I just checked Rockauto and they are different part numbers.

 

Thanks man I'll throw it back in and give it a shot this evening!

 

It's a 5v square wave signal so a digital meter may not react fast enough to catch it. If you have a scope, the trailing edge of the fourth window at each station is 4* before TDC so you can check to see if you have the right plate. Personally I think the only differences in the 2 plates is the bolt pattern for the converters, but I may be wrong. They are both the same diameter. Did you check the replacement plate to make sure the window ring wasn't bent? If it was used, they can get bent just by setting the engine on the floor before removing it.

Since the CKS is a Hall-effect magnetic switch, the strength of the magnetic field is important to weither you get a clean signal or not. A Mopar sensor uses a neodymium magnet and a screwdriver will stick to it strong enough to lift it. Buying one is money well spent.

 

Thanks man, got the new sensor in and she fired right up. Granted she has a misfire but I'll just add that to the list to be fixed on this heap. But at least she is moving now.

Many thanks!