Hoping to get advice with this (speedo and O/D question) - JeepForum.com
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post #1 of 41 Old 11-28-2019, 04:08 PM Thread Starter
Trippysmurf
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Hoping to get advice with this (speedo and O/D question)

It's been awhile since i had a ZJ and am looking at buying a new one for a grand. The owner says there is just one issue. The speedo will sometimes not work and it will not shift into O/D. It is a 95 limited with a V8 in it. He assumes it just needs a new speed sensor. I remember stories of this issue coming up here and there and was wondering if anyone here can give me some advice on whether or not his claim of the sensor being able to fix it seems legit or not. Thanks in advance as always.

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post #2 of 41 Old 11-28-2019, 04:38 PM
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Incorrect speed signal(s) to powertrain control unit(s) can and will cause issues with electronically controlled shifts like OD on/off and TC lockup. I'm pretty sure 46RH uses both a transmission speed sensor and a vehicle speed sensor. However I'm more familiar with the electronically controled 4xRE- series transmissions, so you better wait for a second opinion from guys like Wingless and a few others with the OBD1- era V8s.

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post #3 of 41 Old 11-28-2019, 05:16 PM
wingless
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The 46RH has a two-solenoid pack w/ one for the lockup and one for the overdrive.

A multimeter may be used to measure the resistance of those solenoids, w/ the likely resistance about 10 Ohms. The three pin connector has a shared common and one pin for each solenoid.


According to the FSM:
Converter clutch engagement in overdrive fourth gear is controlled by sensor inputs to the powertrain control module. In third gear above 25 mph, sensor inputs to the control module that determine clutch engagement and shift timing are:
  • coolant temperature (verifies temperature minimum of 60 F)
  • engine speed
  • vehicle speed
  • throttle position
  • manifold vacuum (to MAP sensor)

It sounds like fixing the speed sensor is a good starting point. Do a visual inspection prior to proceeding, because the part has four possible rotational installation positions and replacing at the correct position is a good practice.

Here is the FSM testing on that part (this is from the AW-4 section, no testing is listed in the 46RH section).
SPEED SENSOR TESTING
Test the speed sensor with an ohmmeter. Place the ohmmeter leads on the terminals in the sensor connector (Fig. 37).

Rotate the transmission output shaft and observe the ohmmeter needle. The needle should deflect indicating the switch is opening/closing as the rotor moves past the sensor (Fig. 37). Replace the sensor if the ohmmeter does not display any kind of reading.

If a digital ohmmeter is being used, the sensor should generate an ohmmeter readout each time the switch opens and closes.







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post #4 of 41 Old 11-28-2019, 05:25 PM Thread Starter
Trippysmurf
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wingless, so does that mean the speed sensor is a likely culprit for this issue?
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post #5 of 41 Old 11-28-2019, 05:29 PM
wingless
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Read my updated post...

Yes, get the speed sensor to work first. It MUST work for the OD to also work.


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post #6 of 41 Old 11-28-2019, 05:43 PM Thread Starter
Trippysmurf
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well the current owner says the speedo stops working now and then and the OD doesn't turn on. does that sound speed sensory to you?
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post #7 of 41 Old 11-28-2019, 05:53 PM
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My bad, I kept my crystal ball on the top shelf in the workshop. It was fine until I started hammering on something w/ my BFH. Not surprising that it rolled and crashed! Now I am unable to gain cosmic wisdom.

Back to the issue...

It should work, something(s) are making it not work. Go through the possible options and verify / repair until all the required systems are working properly. It should / must work after all the required systems are operational.


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post #8 of 41 Old 11-29-2019, 12:46 AM
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Garage
...
i USED TO WORK FOR A Chrysler dealer about 11 years ago .. So back when a lot of these Jeeps still were brought into the Stealership for repairs. . I wish I could remember all those transmission codes we dealt with .. But my best memory is your close to correct . So I say if you like the Jeep & it's good buy it &have it fixed if you can't yourself.
... Now back to the problem . We charged about 250.00 to replace both of those sensors in that trans . & You got new fluid & you could pay for a new filter.
... But always remember He forgot to tell you It won't go into reverse when cold for 5 minutes after 1st crank in the morning .
Oh Sir now you need a new trans . Good news is we can overhaul it for you . Only $2000 more but good news is you needed that other stuff also..
Good luck. but I'd take a gamble on that one.
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post #9 of 41 Old 11-29-2019, 05:52 AM
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Quote:
My bad, I kept my crystal ball on the top shelf in the workshop. It was fine until I started hammering on something w/ my BFH. Not surprising that it rolled and crashed! Now I am unable to gain cosmic wisdom.

LMAO! This seems to be the case with a lot of posters here. We do not have crystal balls to look into to diagnose or help with your issue without info. As previously said the pcm needs to know what speed the vehicle is moving at to engage the OD. The OD will engage at approximately 45 mph.
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post #10 of 41 Old 11-29-2019, 01:31 PM Thread Starter
Trippysmurf
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so i got the vehicle now at my house. the OD wont engage for sure at 45 as it goes to 2500-3000 rpms on the highway. The speedo sensor with the gear at the end of it has been replaced with a working one and the issue still is there. The speedo needle wont move till i am driving a bit then it starts. the RPM though read fine. My main concern is trying to get this OD to engage more then anything. If the speed sensor on the side of the trans/tcase is new and such then any advice on a next step?
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post #11 of 41 Old 11-29-2019, 01:34 PM Thread Starter
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Not sure if this relates, but when i go on the highway and the rpm go up to 2.5 to 3k the oil pressure rises quite a bit also to about 60-70 on the guage.
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post #12 of 41 Old 11-29-2019, 01:53 PM Thread Starter
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Also no codes at all by the way
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post #13 of 41 Old 11-29-2019, 01:59 PM
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Quote:
Originally Posted by Trippysmurf View Post
so i got the vehicle now at my house. the OD wont engage for sure at 45 as it goes to 2500-3000 rpms on the highway. The speedo sensor with the gear at the end of it has been replaced with a working one and the issue still is there. The speedo needle wont move till i am driving a bit then it starts. the RPM though read fine. My main concern is trying to get this OD to engage more then anything. If the speed sensor on the side of the trans/tcase is new and such then any advice on a next step?
Was the replacement rotation orientation set to match the original?

Does the replacement measure correctly when tested per the previous FSM information?


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post #14 of 41 Old 11-29-2019, 02:02 PM Thread Starter
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the previous owner replaced the speed sensor 2 days before i got it i found out. he has 2 other zj and 2 other jeeps on top of that, so I would think he would know how to do it, but is there a way to check for sure for myself? he got the speed sensor brand new.
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post #15 of 41 Old 11-29-2019, 02:08 PM
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Quote:
Originally Posted by wingless View Post
It sounds like fixing the speed sensor is a good starting point. Do a visual inspection prior to proceeding, because the part has four possible rotational installation positions and replacing at the correct position is a good practice.

Here is the FSM testing on that part (this is from the AW-4 section, no testing is listed in the 46RH section).
SPEED SENSOR TESTING
Test the speed sensor with an ohmmeter. Place the ohmmeter leads on the terminals in the sensor connector (Fig. 37).

Rotate the transmission output shaft and observe the ohmmeter needle. The needle should deflect indicating the switch is opening/closing as the rotor moves past the sensor (Fig. 37). Replace the sensor if the ohmmeter does not display any kind of reading.

If a digital ohmmeter is being used, the sensor should generate an ohmmeter readout each time the switch opens and closes.
Quote:
Originally Posted by Trippysmurf View Post
the previous owner replaced the speed sensor 2 days before i got it i found out. he has 2 other zj and 2 other jeeps on top of that, so I would think he would know how to do it, but is there a way to check for sure for myself? he got the speed sensor brand new.
Start with this...


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