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code po740

Cherryokeee

NAXJA Forum User
Location
camano island wa
My jeep is a 1998 xj
What would be the best way to fix this with out spending a ton of money.
po740 torque converter clutch,circuit malfunction.
Thanx ahead of time for any and all help:patriot:
 
Start with a multi meter, ohm volt meter, and get the wiring layout. Could be wiring, could be #3 solenoid which is easy to swap. Also could be a bad brake switch, stuck on.
 
Realy it can be all that no one has got any other input on this .Could be this could be that start with this start with that .Can I get a easer fix then that.Com on it like I can do some stuff but come on .
 
Realy it can be all that no one has got any other input on this .Could be this could be that start with this start with that .Can I get a easer fix then that.Com on it like I can do some stuff but come on .

Really.

Ecomike is one of our resident experts, so I would listen to what he says.

You have 3 choices.

1: Do as he says. Get some tools, investigate, learn, fix it.

2: Drop it off at the dealer and pay them to fix it.

3: Sell the truck.

Judging by your last post I'd say go with #3....

Cherokees are finicky and sometimes problems arise that require you to actually get your hands dirty and use that organ between your ears. Sounds to me like you want someone to wave a magic wand and fix your truck for you.

Since you seem too lazy to do it, I googled it for you. Took 2.4 seconds:
P0740 CHRYSLER - Torque Converter Clutch Circuit

Possible causes
- Low transmission fluid level
- Dirty transmission fluid
- Faulty torque converter clutch solenoid valve
- Torque converter clutch solenoid valve harness or connectors
- Torque converter clutch solenoid valve circuit is open or shorted


Help with this

When is the code detected?

Torque Converter Clutch (TCC) unlocked for 10 sec., ECM commands converter lock-up and did not record engine speed drop.
Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- Transmission shift shock
- Vehicle may not shift into the highest gear



P0740 CHRYSLER Description
The torque converter clutch solenoid valve is activated, with the gear in D4, by the Transmission Control Module (TCM) in response to signals sent from the vehicle speed and the Engine Control Module (ECM). Lock-up piston operation will then be controlled. When the torque converter clutch solenoid valve is activated, the torque converter lockup clutch will engage creating a 1 to 1 RPM ratio between the transmission input shaft and the rotational speed of the torque converter.

Lock-up operation, however, is prohibited when A/T fluid temperature is too low.

When the accelerator pedal is depressed (less than 2/8) in lock-up condition, the engine speed should not change abruptly. If there is a big jump in engine speed, there is no lock-up.
 
OK well thanks for more input. Just thought with being a xj page. That someone else has had to of came across this code and fix it.Without taken it to the dealer. But thats cool was not being lazy or haveing attitude just was asking for more input .
thanx
ps sorry if my post came across any other way.
 
Yeah, your post came across a bit snotty, But you're big enough to apologize which is awesome. So let's move on....

Unfortunately the p0740 code is not super specific.

As EcoMike said, search around NAXJA and you should be able to find instructions on how to probe the connectors for the lock-up solenoids in the transmission without dropping the pan.

There are 3 solenoids, so you will have to check each one. If they check okay, then move on to the wiring harness looking/probing for broken wires. If that checks okay, then it could be a faulty TCM, stuck brake light switch, or anything else in the list I gave you above.

You did check the fluid level already, right?

Are there any symptoms other than the CEL? On my '98 when the solenoids started to fail the transmission would not go into overdrive. It would stay in 3rd gear all the time on the freeway.

If it ends up being the solenoids there is a write up on where to get them and how to install them. Search for it, it will save you about $400/$500 over what the dealer would charge and it's super easy to do.

HTH, and good luck.
 
Unfortunately the p0740 code is not super specific.


Unfortunately 90% of the Jeep/Chrysler codes are not super specific!!

Good luck on this one OP. Half the fun of owning XJs are working by a process of elimination and beating one of these codes yourself!
 
First thing to check is the brake switch. It tells the TCU if it is OK to lock up the TC, or not. A bad switch or wire knocked loose is easy to check and fix. Low Tran fluid is an easy check. Also burned fluid is a possible issue, cause.

Then the next probable issue is #3 solenoid being bad (should be about 14 ohms across the coil, if good), or look for wiring damage or dirt between it and the TCU, loss of ground or loss of power. Pull the pan and filter (just a bunch of bolts to remove) and the solenoid is held on by 1-2 screws. Also easy to reach and test and swap if bad.

Lots of good picture threads and wiring info on this in older threads here. Search for posts on "AW4 TCU torque converter lawsoncl naxja.org" in Bing or Google for the threads.
 
Unfortunately 90% of the Jeep/Chrysler codes are not super specific!!

LOL, Kinda like a "Danger Will Robinson" message, LMAO!!!! So true!!! Robot never tells him what the specific danger is!!
 
Last edited:
Transmission Solenoids-Checking

There a way to check the AW4 transmission solenoids without dropping the pan. It’s not foolproof because high resistance may be caused by loose/corroded/dirty connections, etc.

There are two connectors at the firewall (passenger side) that go to the transmission. They will be either both black or one black the other grey, in either case one will be an 8-way, the other a 6-way. You’ll want to check the 6-way. Pull the connector apart and with a digital meter grounded to the negative post of the battery read the resistance at the terminals leading to the transmission. All three should read between 11-15 ohms. That’s a narrow operating range, so touch your meter’s leads together and see how much resistance is in your meter’s leads. The will also be some resistance through the connectors and the wires leading to the solenoids, but my guess is that if the connections and wires are good there shouldn’t be more than about one ohm of resistance.

The other way to check is to pull apart the wire harness at the TCM (transmission control module) usually referred to as the TCU. Look or research for its location. The harness connector should have 26 cavities, two row of thirteen. The solenoid cavities are on the top row (with the harness lock facing up), the last three on the right (#11, 12 and 13). With a good chassis ground measure the resistance from the cavities to the ground. I’m not sure what years this applies to but it is the way my ’97 is set up.

However, if you’re in need of a transmission service the best way to check the solenoids is to check their resistance at the individual solenoids by pulling the connectors off and checking the resistance from the male spade connector on the solenoid to the bracket. Keep in mind that it may take anywhere from overnight to a week to get a replacement part so your vehicle may be down for a while if you find a bad solenoid. Prices vary wildly from about $80 to $240, Jeep and NAPA are the most expensive, but you usually get what you pay for.
 
My tranny is throwing the same code, I couldn't get it through emmissions in the twelve days they gave me so I faked out the tranny and drove it in third until the monitors set and got through emmissions.

Now I'd like to fix the issue. I tested all the solenoids and came in at about 6 ohms at the tcu. I dropped the pan and did the filter and the fluid with no change. I also cleaned the NSS and cleaned all the connectors and dielectric greased them.

I bought this jeep with 92k about a month ago. I was given all the receipts with the jeep when I bought it, the transmission was given a full rebuild and new torque converter in 2009 @ 80k miles, by a fairly reputable shop. The jeep sat for 3 years before I bought it. Only issue left is the p0740 and it makes a rotational noise when the jeep is held with the brakes in any gear but park and neutral. I'm beggining to think I have a bad torque converter but would like to exhaust any other possibilities before I pull the trans.

This article leans me toward the TC I just don't know if maybe the malfunctioning solenoid that is throwing the p0740 is really the culprit.

http://www.freeasestudyguides.com/a2_2.html

Since I've been driving around with the selector in third I haven't gotten the code also.
 
Ok pulled pan (again) tested each solenoid on the tranny, all read at just about 13 ohms. Also put 12v to each solenoid and each one made a "click".

Only other options really (correct me if I'm wrong)

TPS, possibly failed but still does not explain the noise.
Brake switch, possible but again does not explain the noise.

At 50 mph with brake applied no rpm boost, no lock up.

If I drive in third, code never sets (p0470)

I suppose it's time to pull the trans and replace the TC.

Not looking forward to it but it is what it is.
 
13 ohms at the solenoid, and 6 ohms measured earlier at the TCU for the same solenoid indicates a wiring short to me.
 
Yeah, thanks for reading that. I'm so stressed about it it's hard to focus.

I'm gonna trace some more wires today if the wife will let me get some garage time.

The rotational noise still does not fit into there being an electrical problem though

I'm also contemplating sending 12v to the lockup solenoid from the TCM plug. And listen for the click.

All other gears shift normally and smoothly. I pulled the inspection plate again today and the flex plate was clean bolts tight and no cracks.
 
13 ohms at the solenoid, and 6 ohms measured earlier at the TCU for the same solenoid indicates a wiring short to me.

I just re-read some of your earlier advice for the OP.

I'm gonna pull the brake switch again, I haven't looked at it but I'm guessing its just breaking the 12v to solenoid #3.

I'm going to try the cruise control to morrow and see what it does.

Thanks for the help.
 
If there is a weak grounding of the power wire to say solenoid #3 via a damaged wire that is rubbing on a dirty grounded frame, and yielding the lower ohm reading it

(partial short, not enough to blow a fuse but enough to screw with the power feed to the solenoid and drop the voltage to the solenoid below a critical voltage)

can be acting like a parasite, intermittently make the solenoid try to engage but not quite making it, causing a buzzing sound, thus a mechanical noise.

This is based on the variation in the ohm readings!!!!

Also a dirty brake switch stuck thinking the brake is on might be doing exactly this.

Were all three solenoids reading 6 ohms at the TCU, or just #3?
 
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