98 XJ threw a 0700 & 0740 code. Checked lock up solenoid and it was bad. Changed all 3, cleared codes and figured it fixed. 3 days later threw codes again. 0700 & 0740. Pulled solenoid again, tested it and it worked fine, cleared codes and tried again. Threw code 0740 again. Replaced TCU and checked plugs in wiring harness. Threw 0740 again. I'm at a loss. Any ideas?

 

Does the OD ever lock-up when driving?

How did you test the solenoid?

What plugs did you check?

Is there any pending codes, such as P0122?

~~~~~~~~~~~

You may have a bad brake lamp switch, bad TPS signal to the TCM, or wiring from the TCM to the Lock-Up solenoid.

~~~~~~~~~~~

Tests:

You'll need a digital Volt/Ohmmeter.

Refer to the TCM connector pin-out below.

Preliminary

Disconnect battery ground cable at battery. Leave disconnected during the Ohmmeter checks.

Access TCM and unplug the connector.

Check the TCM ground circuit by probing pin cavity 24 (+) to a good chassis ground under the dash. You should read continuity, but no more than 1.0 Ohm resistance. If you see high resistance, the TCM ground point connection should be checked/cleaned. The TCM is grounded at the coil mount bracket stud(s). Two small wire ring terminals and a battery ground cable. Remove and clean the two small ring terminals. Reconnect and read the resistance again.

Brake Lamp Switch

Probe pin cavity 23 (+) to cavity 24 (-). You should see continuity. Move the brake pedal in and out and see if the reading changes. If so, replace the switch. If you see resistance of more than 5.0 Ohms at any time, replace the switch.

Solenoid 'C' circuit wiring

Measure the resistance between cavity 11 (+) and 24 (-). You should see 11 to 15 Ohms resistance (solenoid resistance spec). With a new solenoid installed it should be within spec. If not there may be a wiring fault between the TCM and the solenoid.

TPS Checks

If any fault was found and corrected in the above checks you may not want to be bothered with this check.

To proceed,

Reconnect the battery ground cable at the battery.

You'll be checking the TPS output voltage to the TCM.

Set voltmeter to 20 VDC scale.

Turn ignition switch to ON (run) without starting the engine.

Measure the TPS input voltage by probing cavity 17 (+) to cavity 16 (-). At idle you should read between .26 V and .95 V. While still connected, depress the gas pedal slowly to WOT and watch the Voltmeter. The voltage should increase smoothly to 4.49 volts, or less.

You may not have been experiencing TPS performance problems but the lack of good voltage to the TCM may cause your problem.

Completion

Disconnect the battery ground cable before reconnecting the TCM connector.

Tell us what you find.






.

 

Does the OD ever lock-up when driving?
It seems to drive just fine and I believe it locks up ok. I don't have a tach on it to be 100% sure.

How did you test the solenoid?
I removed it and put 12v to it and it functions. The old one did nothing.

What plugs did you check?
Plug to the TCU and the one near the firewall on passenger side that goes to trans.

Is there any pending codes, such as P0122?
Only code is 0740 with 0700 a couple times.

Thank you for all that info. I'll print it out and get started ASAP. If my answers to your questions change anything please let me know. Thanks again, Mark

 

Your answers create no changes.

If you don't get the correct resistance when checking solenoid 'C' don't reconnect the TCM, you will probably want to go to the connector near the tranny dipstick and take resistance readings from there in an attempt to isolate which section of wiring has the problem.

Same if there's a problem with the TPS voltage readings.

Here's a pic of the solenoids connector:



.

 

I was having similar issues with my son's Jeep,It all started when I installed an overhead console from a Dodge Caravan. It was getting 0700,0704 and a few others,and It would not start on first crank and had to prime a couple of times and then start.Cleaned and re-install NSS,remove tank and install a new filter,no change.Check fuel pressure is was fine.

When he stop the Jeep would jerk.Last week went to the JY to get some parts for my other son Honda,and went and check the Jeep section and found a 1999 Jeep overhead console bought the trip computer ($5.00)and installed it on my son's jeep,and all the codes and problems were corrected.Another site said that the trip computer from the caravan would work on the Jeep.
The PCM work's in mysterious ways.

https://drive.google.com/file/d/0B2C...it?usp=sharing

 

Read this:

http://repairpal.com/OBD-II-Code-P0740

In light of this data you may want to check your Input Speed Sensor from the TCM connector.

Using your Ohmmeter, read between pin cavities 1 and 2. You should see around 650 Ohms.

You can do the same for the Output Speed sensor if you like. Cavities 3 to 4. Same resistance.

Speed Sensor locations:

 

Wow, reading that link is enough to make a country boy like me head spin. I have tomorrow free so I'll be checking everything then. Sure hope I find something.......and thank you for all this info. It's great. Mark

 

Ken,
I checked ground and found a little resistance, I think 3 or 5 ohms. Cleaned it up and read 0 after that. Checked the brake light switch to ground and the first time it was 5 with pedal up and jumped up with pedal down. Second time I tried it it was 0 pedal up and 96 down. The info states any reading over 5 replace. Isn't the the purpose of a switch though? Off and on? Is it really possible this will cause of my trans code? I don't see the relationship but these computerized buggers never make sense to me. Thanks in advance, Mark

 

Also Ken, I just checked the input speed sensor which should be around 650. I show 604 but I don't know if that qualifies as around or not. In just reading your post again I see I was supposed to read it between pin cavities on the TCU plug. I went under and unplugged it and tested directly on the pins themselves. Thank you, mark

 

The pupose of checking it from the TCM connector was to see if the entire circuit from the TCM to the speed sensor was serviceable. Going directly to the speed sensor eliminates the rest of the wiring from the test. But, oh well, 604 Ohms may be okay. Depends on the ambient temp at the time of testing.

 

Sounds like the brake lamp switch is faulty.

One set of contacts in the brake lamp switch provides a ground path 'sense' circuit for the TCM and the PCM, to let them know that either you intend to stop the vehicle or not stop the vehicle. If the intent is to stop the vehicle (depressing the brake pedal) the TCM will see a loss in the ground path and open its electronic control over, in this case, the lock-out solenoid. When the brake pedal is not applied the contact in the switch is closed, when the brake pedal is applied, the contact is opened. See diagram below.



Here's how to change the brake lamp switch (below). Note that it says to pull the plunger out. NOT. New switches come with the plunger fully extended already. Never attempt to push the plunger in then try to pull it out. As seen at the bottom of the instructions, it ratchets in to place, and if you monk around with it and cause it to ratchet in...Say Good Night Gracie, and buy a new one.

To access the switch, remove the trim panel and knee block from around the bottom of the steering column.

I bought my new switch from Advance Auto Parts.

 

WOW Ken, Where did you learn all this? I'll be buying a new switch today and give it a try. I'm amazed at the complexity of these computerized systems. I couldn't even imagine a newer car. Thank you VERY much for you insight and for taking the time to pass it on. I'll post again to hopefully let you know it worked.
Mark

 

Ken,
Have driven the jeep to Kingsport twice now with no code. Although I won't bet my life on it the bugger seems fixed. Thank you so much for your help. ~Mark

 

Mark,

Always glad to help.

Could you summerize what you did to fix it.

Brake Lmp Switch?

 

Ken,
Yes I replaced the brake lamp switch but I spoke too soon on the fix. Yesterday it threw a code 0740 & 0700 both. I'm at a loss with this thing. I still haven't checked the TPS output voltage to the TCM as you recommended earlier so I'll do that next. After that ????
Mark