Ianf406

Hey guys- So I've dealt with it for quite awhile but I am about to drop a stroker in and want to get it fixed. I have a 99XJ, ~165K miles, auto trans.

Every other time I turn my Jeep on, when in D, I am in overdrive. Goes like this to better explain.

Turn on, put it D- shifts into final gear at about 60/65 and 75 is around 2200rpm-->
Get to destination- Turn off
Turn back on, put it in D- shifts into final gear at around 50 and 75 is around 3400rpm.

I have tested this tons of times by pulling off the road, turning it off then back on and continuing down the road. Every other time it has overdrive. The other times it does not. I actually will turn it on/off/back on depending on what road I am going on. Haha parked today in the high rpm mode so tomorrow morning will be in OD. I am not the only one that has had this issue but none that I can find have a resolution.

I adjusted the kick down sensor and have changed the fluid several times. I am going to put a new HD torque convertor in it and a new filter when I pull the engine. Any ideas?

Ianf406

Nothing huh? I get the same thing from my mechanic buddies and none of the other threads about this issue were answered either. Weird. Maybe Ill just get a new tranny too.

letsgomuddin

Either the torque converter or the tcm is bad, id lean towards the tcm myself.

Ianf406

Thanks. I did not know about the TCM. Little research and I found out where its located/what it does etc. Is there any difference between them within the same year/transmission? Like If I buy one from a 99 part out on here with the auto it should be the same right? To give it a shot. I see they are like 150-200$ online refurbished. Thanks again.

letsgomuddin

Should be the same if from the same year, even a few years are compatable, Far as I know all 97-01 tcm are the same so the pre 97 ones ars probably the same as long as they have the aw4 trans.

Easye1986

I have the exact same issue. Its every other key cycle OD works.

Ianf406

What have you tried so far?

Easye1986

Im in the process of a slow flush on the trans, and reading about similar problems. Do you have any Codes

Ianf406

Only for o2 sensor- which I replaced but code keeps coming back. I supposed I could run it in (I don't have a computer) and get it ran again But I've had the problem for along time. (before any codes)

Ianf406

Okay thanks. Ill try to grab one on here and see if that works.

Ianf406

Any other ideas? Im going to try the tcm but any other ideas?

Anony

I'd have to ask where your normal shifting (mph / rpms) for OD should be .. and where are you shifting in 1st, 2nd and 3rd.

With a small payload on a flat road, normal acceleration, while in (D)rive my OD kicks in around 44-45 mph @ ~2000 rpms then drops back down to around ~1500 rpm .. * Shifting (1, 2, 3 & OD) mph & rpms vary somewhat depending on where the T.V. cable is adjusted and how fast the acceleration.

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Links to similar problems ..

Overdrive every other time it starts

https://www.cherokeeforum.com/f2/ove...-starts-96613/

Problem: Jeep doesn't like overdrive...sometimes

https://www.cherokeeforum.com/f2/pro...ometimes-4312/

___________________

Taking a look at some of the components used by the TCM, you have ...

Connectors ___

TCM connector
TPS connector
Transmission 8-way solenoids connector
Transmission 8-way TRS connector

_ TPS is ok? (the TCM uses the TPS to determine shift points.)

_ TCM wires & connector (pins) ok?

_ TRS (NSS) transmission range sensor ... ok?

The TCM uses the TRS to determine the shift lever. If the TRS has a faulty signal, the TCM defaults to 3 range, unless no signal is detected while in 3 range the TCM will default to OD.

Can't think of why on / off would effect the rpms for OD shifting, other than its having an effect on the TCM and/or one the components.

TRS (trans. range sensor, NSS) === (OD sense) === TCM

Faulty TRS (NSS) **

** The only problems I have ever had with a faulty TRS/NSS is while starting and backup lights, the contacts inside the switch become dirty and need cleaning, sometimes the lubricant inside drys up causing poor switch contact. The engine has problems starting in Park or Neutral ... and the backup lights may only work intermittently or not at all.

** If the TRS/NSS is suspect causing shifting problems ... I would first inspect the TRS/NSS plug inside the engine compartment for corroded and/or bent pin contacts, shorts, crossed wires in the harness and plug

If 1-2 range is detected with OD, 3 range is used
If no signal detected TCM will use OD as default (while in lever 3 range)
If 3 range signal is on with OD or 1-2 , 3 range is used
If no signal while in OD 3 range is used
If OD range detected with 3 or 1-2 ... 3 range is used (disables OD)
If no signal detected TCM uses 3rd shift as default (disables OD)

Speed Sensors

ISS (input speed sensor) ==== TCM
OSS (output speed sensor) === TCM

TCM uses ISS & OSS to determine gear ratio

Solenoids

TCC solenoid --- TCC control (torque converter control)
Solenoid 1 ------ controls 1-2 shift & 3-4 shift
Solenoid 2 ------ controls 2-3 shift

Solenoid 2 sticking, effects solenoid 1 and TCC solenoid operations.

Brake Lamp Switch Connector ...

NO (normaly open) switch held closed - brake pedal released ... switch sense inputs ----> PCM and TCM.

Cav: 1 - WT/PK ... = Brake/Stop Switch Sense (voltage > 10 volts)
Cav: 2 - BK ......... = Ground (resistance to gnd < 5 ohms)
Cav: 3 - YL/RD .... = S/C Power (Vehicle speed control on/off sense)
Cav: 4 - DB/RD ... = S/C Brake Sw. output (Vehicle speed control brake sw. output)
Cav: 5 - WT/TN .... = Brake Lamp Sw. output
Cav: 6 - PK/DB .... = Fused B+

Battery voltage: TCM operates normally when (#16 PDC) fused B+ voltage is between 10.0 & 17.7 volts.
If voltage to TCM becomes out of range transmission defaults to 4th gear limp in mode.


There are also linkage adjustments that can be double checked for correct operation.
____

Appears there were some changes made to the TCM in 98 (ISS) ... uncertain if a 99+ TCM will work with 98 PCM.

cruiser54

Possibly the brake switch, which disengages torque converter lockup, is out of adjustment? It's located up near the brake pedal pivot. The white one.

kjc

X2 what cruiser54 said.. Check cheap/free fixes first. Nice pic too

Ianf406

Thanks guys Ill find out how to and check the brake today. I have a newish tps sensor(maybe a year old). The replacement of that had no effect on this issue. Thanks Anony for all the info. Definitely gives me more to look into. I might replace the TRS as well after checking the break.