Crankshaft Sensor breaking in half

JUSTINO94

MEMBER
2007 INFINITI G35
3.5L
V6
2WD
AUTOMATIC
116,000 MILES

In January my car stalled and had to be towed to my house. I used my scanner/code reader to diagnose the problem considering I do all the mechanic work on my vehicle myself. I got the P0335-Crankshaft Position Sensor A Circuit. I bought a new OEM sensor from the dealer and installed it. While installing the new one, my father over tightened the bolt and broke the harness/plug that locks the harness onto the sensor. I used electrical tape to secure the harness while I waited for the new Pigtails to come in the mail. Fast forward 3 months, its late April. Everything mechanically has been fine with the car. I never did install the new pigtails yet though I have them in my car just waiting. Last Saturday my son and I were just about home after going for breakfast when I heard a "clunk". Immediately my car stalled and the traction control light and the check engine light illuminated. Having this problem a few months back I knew exactly what it was. I pushed my car home, reached where the sensor was and found the sensor still taped to the harness but the bolt holding the sensor into the block was gone. I assumed the bolt somehow backed itself out, so I purchased a new bolt and reinstalled the sensor. She fired right up once that was done. My son and I jumped in and got about 3 blocks, as I pushed the accelerator more than I have the previous 2 blocks, I once again heard the "clunk" and stalled. I reached back down the engine bay and found the sensor still tapped to the harness except the eye on the sensor was broken off, and the sensor was cracked in half.

My question is, what could be causing the sensor to be knocked out the block? Was the sensor cracked after the first time it "backed the bolt out" and it cracked in half the second time from the previous wear? Is the flex plate bent somehow touching the sensor when spinning? If so, wouldn't it hit it every spin and not just when applying more throttle than at idle?

I need to know where to start looking these sensors are $90.00 a piece and I can't keep replacing them not knowing the culprit.

3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

There are a number of things that come to mind but the thing that makes the most sense would be the flex plate is loose and moving or the crank bearing is allowing the crank to walk, and it ends up contacting the sensor.

The way to find this out is to look at the tip of the sensor and see if there are witness marks of the flex plate touching the sensor prior to it breaking.

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

In other words, we need to rev the engine slowly so that the sensor does not break and then inspect it for marks.

This would make the most sense just because of what you said that it doesn't do it all the time. So, if it only does it when revving the engine then it would make sense that the additional RPM is causing the crank to move.

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Wednesday, April 13th, 2022 AT 3:07 PM

JUSTINO94

MEMBER
2 POSTS

I will mention when the car was purchased there was a rattle at idle that turned out to be 1 single bolt holding the torque converter on. I purchased OEM bolts and used Loctite and a torque wrench tightening to spec. Could the previous bolts be jumping around in the bell housing? If so, how do I go about removing any loose parts from the bellhousing? What would be the best way to go about it? There’s no noise or anything indicating loose parts bouncing around, but I am no mechanic! Could it possibly be a warped flex plate from the wear of having 1 single bolt in the converter for some time before I bought it? Again, if this was the case there isn’t any warning signs or symptoms or sounds when it happens. There’s a thread on Reddit of a guy saying the EXACT same thing but he doesn’t put his updated with a fix. It went awhile the first time replacing but now is happening right away. Lastly, if I feel inside the crankshaft hole with a finger, I can feel the crankshaft teeth. It’s a ring with spaced out teeth that I suppose spins with the flex plate and rides past the sensor closely. Initially I was thinking due to the wear from the faulty converter one of those teeth are bent hitting the sensor? I wanted to spin the engine while using a rod inserting it the depth the sensor would go to see if any teeth hit or at least see if any rode closer than the others. If so I would attempt filling back a tooth a little?

If all my ideas are incorrect, I will attempt to inspect the sensor while slowly revving the car and checking for marks. But these sensors aren’t cheap! If your guess is true, what would be my next step to replace the
Walking crank? I’m aware of how to replace the flex plate. I purchased one when inspecting the converter and planned to replace it. I had all the transmission bolts removed and all the accessories that needed to be removed and I still couldn’t get the transmission to break free from the engine. It’s stuck on the dowels/pins I suppose. That’s when I noticed the converter was missing bolts. So, I replaced them through the little window on the bottom side of the bellhousing and returned the flex plate because the car ran perfect after replacing bolts. I’m mentioning everything I can to give you a better understanding of exactly what’s been going on in hopes of getting some genuine feedback & ideas before I run myself crazy fixing this and fixing that to find a problem that could be as simple as filing a tooth back? Thanks for any feedback by the way! I really do appreciate you!

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Saturday, June 4th, 2022 AT 1:49 PM

KASEKENNY

MECHANIC
18,907 POSTS

Yeah. It very well could be a flex plate or crank issue.

Can you get a picture of the broken crank sensor so we can see how they are breaking? That will help tell us what the possible issues are.

However, I would take a new crank sensor, put in the hole, and do not bolt it in. Then hold it with your finger and have someone turn the engine over by hand with a socket on the crank pulley. If the flex plate is contacting it, you will feel it.

There is a chance the issue will only happen when the engine is running but hopefully you will feel it touch the sensor which will confirm this is the issue.

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Saturday, June 4th, 2022 AT 3:36 PM