Thread: Transmission: Check your speed sensor!!

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  1. #1 Transmission: Check your speed sensor!! 
    Senior Member MallCrawlin Supporter zj-monster's Avatar
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    Not too long ago I was wheeling around in the nasty sand pits of my town. Shortly after I noticed that my check engine light was on. I checked and checked (or so I thought) but eventualy gave up looking for the problem since I thought my jeep ran just fine. lately though, I've noticed that my tranny wants to stay in second for about 30 seconds to a full minute.

    Tonight (it's 11:42 pm...btw) I decided to change out the tranny fluid in the 42RE in hopes of solving the shifting issues. While looking around under the tranny, lo & behold I see that I knocked a speed sensor off just above the crossmember on the transmission.

    Just follow the photos and you'll see.



    How I did this while wheeling is a mystery to me since the cross member is right below the sensor. The tip of the sensor is magnetic. If you look on the tip, you'll notice some slick, silver, fuzzy looking material...that's metal shavings!! Oh yea...but my jeep has well over 150,000 miles on her.



    Here is the orientation...



    Earlier I had very hard time trying to figure out what this sucker is. After hardcore searching on the internet & going to the dealership where rob works (damn it...he was off today) one of his co-workers instantly recognized the part and asked me how my tranny was shifting. Ah...the irony. In this case, this sucker is an Input/Output Speed Sensor for the 42RE Tranny.

    The Input and Output Speed Sensors are two-wire magnetic pickup devices that generate AC signals as rotation occurs. They are mounted in the left side of the transmission case and are considered primary inputs to the Transmission Control Module (TCM).

    * The 42RE transmissions use a single sensor (located on the overdrive gear case, over the park gear).

    * The 45RFE / 545RFE transmissions use two sensors, an input speed sensor and an output speed sensor. Both are the same part number.
    1: The Input Speed Sensor provides information on how fast the input shaft is rotating. As the teeth of the input clutch hub pass by the sensor coil, an AC voltage is generated and sent to the TCM. The TCM interprets this information as input shaft rpm.
    2: The Output Speed Sensor generates an AC signal in a similar fashion, though its coil is excited by rotation of the rear planetary carrier lugs. The TCM interprets this information as output shaft rpm.







    So there ya have it, a little bit of research and now I know. If any of ya'll are having similar shifting problems, you might want to check this part out. From what I have been reading, this part is prone to failure. In my case I managed to rip it out completely. It set me back about 25 bucks.

    Peace.
    Last edited by zj-monster; 05-27-2006 at 02:17 PM.
    Quote Originally Posted by CurtP View Post
    What a fucking concept, eh? How dare you bring logic to this thread. What are you, some kind of asshole?
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  2. #2 Re: Transmission: Check your speed sensor!! 
    Senior Member nate's Avatar
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    Yup. They are about $10-15 from Napa. I have a few extra I've collected over the years... as well as a bunch of tranny parts.
    03 Subaru WRX
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  3. #3 Re: Transmission: Check your speed sensor!! 
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    I lost one a while back too.
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  4. #4 Re: Transmission: Check your speed sensor!! 
    Senior Member MallCrawlin Supporter zj-monster's Avatar
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    It took damn near 30 mins of driving for the check engine light to go off...POS!!
    Quote Originally Posted by CurtP View Post
    What a fucking concept, eh? How dare you bring logic to this thread. What are you, some kind of asshole?
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  5. #5 Re: Transmission: Check your speed sensor!! 
    Senior Member nate's Avatar
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    That's why I have a code scanner. Hard to work on OBD II rigs without one.
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  6. #6 Re: Transmission: Check your speed sensor!! 
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    OverkillZJ's Avatar
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    I busted that my first time wheeling long ago!

    Just reset the ECU next time (pull battery, reconnect.)

    You don't need a code scanner unless you have a 98, since the rest will return the code with the key switch. I have one anyway, comes in handy.
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  7. #7 Re: Transmission: Check your speed sensor!! 
    Senior Member nate's Avatar
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    Yup. Not so much on the Jeep, but on other rigs I have worked on.
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