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Jerry, Master Mechanic
Category: Dodge
Satisfied Customers: 1754
Experience:  ASE Master tech, 30 years exp. troubleshooter, driveability tech
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Again. Got a P1398 code. Replaced the Crankshaft

Customer Question

Hello again. Got a P1398 code. Replaced the Crankshaft Position Sensor. What next? Don't say compression check. Don't say compression check. Don't say compression check.
Submitted: 2 years ago.
Category: Dodge
Expert:  sprinkles08 replied 2 years ago.
Hi again!
This code sets when there is an issue with the adaptive numerator. The adaptive numerator is a measure of the variance between the crank sensor tone wheel openings for each cylinder. A number of things could cause this including a weak cylinder, but hopefully that isn't the case.
You had a tick in the engine a couple months ago, has that been repaired?
Customer: replied 2 years ago.
So good to hear from you, my "brain mechanic". I love troubleshooting, or attempting to do so.The tick was rated as "inconclusive" and "not that bad" by my $89/hr mechanic. He is getting replaced. Nevertheless, no, it was not fixed.The vehicle was sitting for 3 weeks when I decided to drive it a bit, smart yea? Code. Great.What should my next step be? I just rented a compression tester for a rusty shitbeater Ranger I bought (dead #2 cylinder, looking for engines, oops). I could run a compression test.What do you recommend as my next diagnostic steps?
Expert:  sprinkles08 replied 2 years ago.
If you're on a time frame with getting the compression tester back it would be a good idea to get a compression test out of the way while you have the gauge.
Other than that the problem could be electrical or possibly a broken/damaged flexplate.
Was the battery disconnected after the sensor was replaced?
Customer: replied 2 years ago.
I can have the compression tester forever. $40 autozone "rental". I might keep it. Good to have around considering my busted car hobby.No the battery was not disconnected, I just cleared the codes. Then the same code came back.What's a flexplate?What troubleshooting step do you recommend next?
Expert:  sprinkles08 replied 2 years ago.
The flexpate is bolted to the back of the crankshaft and the torque converter is bolted to it. The crank sensor tone wheel is part of the flexplate.
Try a battery disconnect and that will clear the adaptive numerator. Get to an area where you can so some slow speed accelerations and decelerations. Leave it in first gear and speed up to 15-20 MPH, let off and let it coast to a stop. Do this about ten times and then drive it as normal to see if the code returns.
If you have a scan tool that will monitor data you can just do the decelerations until it shows the adaptive numerator has learned again.
Customer: replied 2 years ago.
Okay. I'll try the battery hard reset first. I am, at heart, a lazy man that doesn't want to mess with 8 spark plugs.I don't think my ODBII scanner is that smart. It's one of the LM317 cheap wifi iphone jobs.There was a bit of iron dust stuck magnetically on the old CPS sensor.I'll let you know.
Expert:  sprinkles08 replied 2 years ago.
The dust could be from a broken flexplate but let's try the battery disconnect and relearning the adaptive numerator nd go from there.
Customer: replied 2 years ago.
The battery reset fixed the problem. Code hasn't come back. Thank you.
Expert:  sprinkles08 replied 2 years ago.
You're welcome!