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#1 08-21-2012 15:33:11

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Throttle Position Sensor and Auto Transmission

I am looking at an 89 Cherokee Laredo, and it is having issues shifting out of 2nd Gear, I have heard tales of the Throttle Position Sensor causing this. Is this true, or does it only delay the shifting?

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08-21-2012 15:33:11

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Re: Throttle Position Sensor and Auto Transmission

#2 08-21-2012 15:34:42

kris
Helper
Registered: 10-05-2008
Posts: 30

Re: Throttle Position Sensor and Auto Transmission

A bad TPS is the usual cause for not shifting at the correct rpms, not shifting until a very high rpm, or failing to downshift.  TPS sensors are mechanically similar to a volume knob, and they do wear out, get dead spots, or scratchy.

If it eventually does shift into all the gears then the tranny is probably fine and its just the TPS.  Given that it does shift into 1st and 2nd, the solenoids are likely fine.

On an 89, the trans computer is located under the passenger side of the dash.  It decides when to shift based on the output rpm of the tranny and the TPS sensor.  It's only other input is an extra switch by the brake pedal that tells it to unlock the t/c when the brakes are applied.  As a test that the tranny is fine mechanically, you can unplug the trans computer (or pull the fuse in the wiring near the computer) and you should be able to shift manually.  That is (1-2) will give you 1st gear, (3) will give you third, and (4) will give you fourth.

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#3 08-21-2012 15:35:25

breabsrip
Helper
Registered: 02-13-2009
Posts: 32

Re: Throttle Position Sensor and Auto Transmission

do you mean it's running through 1st and 2nd and then not shifting out of 2nd, or that it's stuck in 2nd and not shifting up or down?

reason i ask is that one failure i had with a Vehicle Speed Sensor on the transmission left my '94 seemingly stuck in 2nd; turns out that's 'Limp Home Mode'.

neither situation above sounds like what i experienced when i had issues with a Throttle Position Sensor, it just wouldn't shift consistently at all. (naturally this was while in the Desert ~100 miles from anything, and several hundred miles from home.) i was, however, able to diagnose it by getting the DTCs off of the Check Engine Light by playing the key-click game, and it seemed to behave itself well enough to get me out after i disconnected it, cleaned it up and reconnected it.

did you check to make sure it's got enough ATF in it?
were you able to get any DTCs out of it?

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#4 08-21-2012 15:40:33

kris
Helper
Registered: 10-05-2008
Posts: 30

Re: Throttle Position Sensor and Auto Transmission

Not to be picky, but the VSS is on the xfer case and used by the engine computer and speedo. The tranny has its own output speed sensor on the adapter/tailcone. If you think about it, that makes sense as the tranny has no idea if the xfer case is in hi or low or neutral.

97+ AW4 trannies also have a speed sensor on the input shaft. The main reason for that is so the tranny computer can diagnose problems such as the converter not locking up, bad shift solenoids, or a bad input or output speed sensor.

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08-21-2012 15:40:33

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Re: Throttle Position Sensor and Auto Transmission

#5 08-21-2012 15:43:10

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

Okay, got to go play with the Jeep:

Jeep will not properly shift out of first at all UNLESS you shift it manually from 1st, to 2nd, to 3rd, to Drive (4th).

This model does not have the vehicle speed sensor, its the old fashioned mechanical speedo cable.

I called a friend and he suggested the Tach, which would unlock the t/c and allow it to shift to the next gear.

I'm not backing down on this Jeep though, shifting through it manually, it shifts clean and is in excellent condition for its age, no body rust to speak of and the engine was just re-built (no relation to the transmission problem).

Toss more ideas my way

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#6 08-21-2012 15:45:23

breabsrip
Helper
Registered: 02-13-2009
Posts: 32

Re: Throttle Position Sensor and Auto Transmission

go ahead; be picky! ;-)

what i'm referring to is a speed sensor that is on the trans; perhaps it's known to you by a different name, but it was what failed on my latest tranny to cause the thing to fail into Limp Home mode.
looking closer at the notes i have from that last failure, it may not be relevant anyway, since it looks like the failure may have actually caused it to lock in 3rd, not 2nd... to add to the confusion, the part that was replaced is referred to by more than one name in the records i have from ChryCo.
any of you that remember what fun it was going through 4 different trannys from Chrysler might not find it hard to believe that they couldn't keep their records or names of replaced parts straight,... ;-*

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#7 08-21-2012 15:47:56

kris
Helper
Registered: 10-05-2008
Posts: 30

Re: Throttle Position Sensor and Auto Transmission

When you shifting manually with the shifter, is the TCU unplugged?  If you're starting out in 4th gear with the shifter in (D), then usually that means the trans computer is not connected or has no power.  If everything is plugged in and powered, it may mean a bad shift solenoid or bad output speed sensor.  http://www.transonline.com/transdigest/ … index.html has diagnostic info for checking the solenoids.  I think the article was written for a Renix era Jeep so the TPS measurement will be backwards.

On the plus side, if its shifting manually then the tranny is good.  The problem is on the electrical side.  If you end up needing a solenoid I have a link somewhere for buying them cheap using the Toyota part number.

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#8 08-21-2012 15:49:23

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

I shifted through manually with both the TCU plugged in and unplugged. The TCU is getting power, as the selector for Power and Comfort on the dash only works when the TCU is plugged in.

How bad is a solenoid replacement?

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#9 08-21-2012 15:50:18

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

I didn't know about that 15 amp fuse they show in that article, I will check that tomorrow or ASAP. That may be the issue, as the 7.5 amp fuse on the fuse box is good.

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#10 08-21-2012 15:52:20

kris
Helper
Registered: 10-05-2008
Posts: 30

Re: Throttle Position Sensor and Auto Transmission

Solenoid replacement is pretty easy.  Drop the pan and remove the filter.  The solenoids are right there on the bottom held on with a single bolt each.  Grab your meter and start checking things at the TCU connector.  That'll tell you the problem fairly quickly.

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#11 08-21-2012 16:54:20

sucram
Rookie
Registered: 02-20-2010
Posts: 94

Re: Throttle Position Sensor and Auto Transmission

If you are getting all the gears manually, then one of solenoids is not at fault. It will be one of the sensors not giving the information or the TCU itself. If you know anyone with a similar model from the renix era, then swap it over and see if it all works then.
Adjust the TV cable

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#12 08-21-2012 16:55:05

evad
Enthusiast
Registered: 10-05-2008
Posts: 218

Re: Throttle Position Sensor and Auto Transmission

from http://www.naxja.org/forum/showthread.php?t=12575
(where another person was having difficulties with his XJ)


Check out my Jeep XJ

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#13 08-22-2012 10:03:00

kris
Helper
Registered: 10-05-2008
Posts: 30

Re: Throttle Position Sensor and Auto Transmission

The throttle body to tranny cable controls the internal hydraulic pressure, thus affecting the shift firmness. It does not control when the shifting occurs. If its way out of adjustment, it can cause very sluggish or no shifting at all.

Unplugging the tcu and shifting manually, takes the solenoids out of the picture, So shifting okay manually doesn't rule out the solenoids, it does verify that the tranny is okay mechanically.

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#14 08-22-2012 10:03:29

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

I'll run an ohms check on the solenoids and see if they are good or short

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#15 08-22-2012 10:04:12

james
Rookie
Registered: 10-05-2008
Posts: 83

Re: Throttle Position Sensor and Auto Transmission

Usually with the solenoids, they either work or don't. Since your trans shifts, just not at the proper time, I'd rule out a solenoid. Most likely its the TPS (which can read fine with a meter but still be off enough to screw with shifting), or the TCU. I had to replace a TCU in my old '88 because of a similar shifting issue.

I wish I had grabbed more parts off a late 80's XJ someone I know scrapped, I could have sent a TPS and TCU your way.

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#16 08-22-2012 10:04:42

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

Well if someone has a spare TCU, let me know. I may just get one to swap in to see if it fixes the issue

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#17 08-22-2012 10:05:31

evad
Enthusiast
Registered: 10-05-2008
Posts: 218

Re: Throttle Position Sensor and Auto Transmission

Please post all of the numbers off of yours. I might have one somewhere in my pile of junk! lol
If I don't someone does. ;-)

Did you check the TPS yet???

Now is there an electronic sensor for the Vehicle Speed on these 1989 XJs?


Check out my Jeep XJ

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#18 08-22-2012 10:05:45

kris
Helper
Registered: 10-05-2008
Posts: 30

Re: Throttle Position Sensor and Auto Transmission

I have seen marginal solenoids cause intermittent problems particulary once they warm up.  They usually measure bad with a meter though.  I lost track of what year we're talking about.  I have a spare 1991 TCU sitting here you can have.  It's the green connector, meaning HO versus the grey connector meaning Renix.

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#19 08-30-2012 10:35:12

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

I cannot find a part number for the TCU, but here is what the connector should look like:

TCU4.jpg

I haven't gotten to test the TPS yet, but it IS adjusting the throttle in response to changes in orientation during idle, so I suspect it IS working

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#20 08-30-2012 10:36:11

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

Oh yes:

No, no electric speed sensor on this one, it uses the old fashioned speedo cable

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#21 08-30-2012 10:36:35

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

The TCU needs to be a Renix model or it won't work

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#22 08-30-2012 10:39:39

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

One thing that discounts the solenoids is the fact that solenoids rarely just FAIL, they degrade. As a solenoid shorts out, it loses is ability to create a magnetic field to push the core. For ALL the solenoids to fail at once, its highly unlikely. I would see sluggish shifting, high RPM, low output. I'm seeing none of that, I believe that discounts the solenoids. It means the solenoids are not getting activated at all, which brings us back to the TCU and sensors

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#23 08-30-2012 10:40:47

evad
Enthusiast
Registered: 10-05-2008
Posts: 218

Re: Throttle Position Sensor and Auto Transmission

I would say that is incorrect and the transmission NEEDS some electric speed sensor to help it shift.

Do you have the repair manual for the transmission?
I have a 1988 Jeep auto trans diagnosis-AW4 copy that I can email to you.


Check out my Jeep XJ

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#24 08-30-2012 10:41:25

Knapper
Helper
Registered: 04-02-2009
Posts: 31

Re: Throttle Position Sensor and Auto Transmission

I have the AW4 transmission manual, but I cannot find the speed sensor on my vehicle, where would it be?

According to the manual:

The speed sensor is mounted on the transmission output shaft and extension housing, the extension housing didn't have any wires as far as I could tell. I will check sometime tommorrow

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#25 08-30-2012 10:42:37

evad
Enthusiast
Registered: 10-05-2008
Posts: 218

Re: Throttle Position Sensor and Auto Transmission

Hmmm was the transmission changed?

The Speed Sensor should be on the 4WD adapter housing between the trans and the transfer case.
Do you see any wiring going to the transmission area, besides the Neutral Safety Switch?
You check the sensor with an ohm meter.

I have 2 manuals for the 1988 AW4
One with 112 pages and the other with 84 pages
.....which do you have?


Check out my Jeep XJ

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