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Galaxie500XL

'95 DOHC Cutlass, P0740, no overdrive, no TCC when hot

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I know I'm probably tiring you folks...but you've been such a help alreay, and I've now resolved almost all the issues my "95 convertible had when I bought it, and it's only been two weeks!

 

Here's the issue...since fixing the Quad Driver module fault this weekend, I'm down to a single DTC showing on my scantool.

 

The car runs great while cool, no codes at all, but a some point, once the car gets warm, the TCC is no longer locked, and the transmission shifts out of overdrive into 3rd gear. That's where things stay. At that point, the scantool shows a P0740 (TCC error), the "Service Engine Soon" light never goes on.

 

I thought at first this could be an issue of the transmission going into "hot mode", but according to the factory service manual, this occurs at temps above 266 degrees. Warmest the scantool has shown the transmission fluid so far is 211 degrees.

 

So far, I've not found any wiring issues...any suggestions?

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interesting. what you describe functionally is overheat limp mode, but you have been able to verify the temperature is not that hot. when did you verify the temperature? was is monitored for the duration of the drive cycle????

 

Overheat limp mode once triggered is permanently set until the ignition is cycled. A single spike of temperature above the threshold would leave the car in limp mode, so if you are scanning the car after you have driven it, you may be missing a temperature spike.

 

 

solutions:

 

Monitor the car from a start and make sure that there is not a quick spike in temperature that is causing oveheat limp.

 

next time limp mode occurs re-start to car and see if limp mode is reset once you are driving at speed going down the road. All you need to do is flick the key off and then right back on, and you will have cycled the ignition and not actually need to place the vehicle in neutral to use the starter, as the engine will still be spinning. Does that reset limp mode for you?

 

 

you may benefit from a auxiliary tranny cooler none-the-less.

 

 

 

next thing: i heard recently that someone fixed this issue by replacing the Neutral Safety Switch on their car. I've successfully opened and cleaned those switches and relubricated them with ease. I'll leave it to you to figure out.

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I was monitoring the temperature from the scan tool...will check the neutral safety switch. I found a Regal 3.8 in the junkyard with the factory transmission cooler, but not certain about it working in the Cutlass. There is an "X" shaped brace in front of the radiator support that isn't on the Regal, not sure if the cooler will clear.

 

Thanks for the suggestions, I'm assuming since it engages properly at least SOME of the time, it may be a relatively simple problem..

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Did a little research, my factory service manuals came in...

 

If the PCM sets a P0740, the PCM disables overdrive and the TCC for that drive cycle. Upon restart, it will again attempt to lock the TCC.

 

Drove it to work today, 20 miles. The TCC locked, and overdrive stayed engaged the entire trip. Lightly tapping on the brake indicated the tcc unlocked, then relocked at an appropriate time.

 

I've got my scantool set to record values if a code is set, we'll see what the conditions are when the PCM sets the code...but at this point, I'm suspecting the TCC solenoid is failing when hot, and the computer is detecting the TCC unlocking inappropirately, and setting the code. If this is the case, looks like I'm going to be taking the side cover off of the transmission, and replacing the TCC solenoid...and from what I gather, it's not a fun job.

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Took the car for a little drive at lunch, checked for codes, none were present...not surprising since it behaved itself this morning...after about 10 minutes of driving, scantool set to record if a code was set, I felt the car shift into 3rd gear. Running 60MPH, throttle 8%, P0740 set. Transmission temp reported as 179 degrees.

 

Looks like it's time to drag out the DVM, and check the resistance of the solenoids...FSM gives figures of proper resistance at 190F...close enough for me to determine if the solenoid is failing when hot.

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Looks as if the TCC solenoid is bad, goes open once the temp raises above 179 degrees. Found a Regal in the local Pull-A-Part with a 3.8, pulled the transmission cooler and all the associated lines for $35.00.

 

Brought the parts home, then the fun began. The Cutlass has no grill, so Oldsmobile built a plenum box from the bumper surrounding the front of the radiator to force air through...the cooler has to go inside the box. Ended up removing the headlight assembly, then taking the plastic retainers out of the driver's side of the box to gain access. Also, the slots for the bottom of the cooler don't match up, had to make a new one on the right side with a drill. Additionally, later convertibles have a welded "X" brace in the radiator opening, careful bending of the cooler brackets allowed for clearance. The left bracket attaches to the dogbone bolt at the front of the bracket, and there's already a hole in the support fo the right bracket.

The cooler lines are a different shape, too, on the Regal, so I ended up using most of the Regal lines, then cut the lines just before they made the bend around the radiator, and used rubber transmission cooler hose, about 2 feet per side, to snake around the radiator support, and into the plenum box to the transmission cooler. There's a gap at the bottom of the plenum box where the bumper attaches that allowed the lines into the box without having to cut holes into the box.

 

The transmission now runs about 15-20 degrees cooler.

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That's a great suggestion, and something I hadn't considered. Thanks!

 

 

Always check the transmission ground cables (or make new ones).

These new electronic transmissions have major problems when the ground path gets compromised.

(its a cheap fix)

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As Special K, or Crazy K said, the neutral safety switch on mine caused a similar condition. But, it wasn't the replacement as much as fine tuning the alignment. To be short: if you can start in neutral, it's aligned and, in my case, solved my TCC problem. A couple of years ago, I added a trans cooler and it seemed to help. But, the dang NSS has to be spot on for mine to lock up.

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The neutral safety switch on mine is an issue, I have to play with the shifter to be able to start in neutral. What's confusing in that regard is that it locks up fine until the transmission temp reaches 179 degrees...but it could possibly be that the shift cable is "growing" as the temp rises. I need to adjust it properly anyway...I'll keep the list posted if this makes a difference. Thanks for the suggestion!

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I know this is an old thread, one I started nearly 2 years ago, but since so many have reported similar issues of no TCC lock/no overdrive with 4T60E transmissions, an update seemed like a good idea.

 

I FINALLY took the car for a full transmission rebuild this past week. Made a huge difference. Shifts are now firm and crisp, the transmission no longer hunts around for the proper gear.

 

However, the P0740 code, and loss of TCC lockup, and loss of overdrive when the transmission reaches normal operating temperatures STILL occurs. The only change is now this does not happen until the transmission temp exceeds 195 degrees. Unfortunately, even with an external transmission cooler, normal fluid temps are around 200-215 degrees on a hot day, or in stop-and-go traffic.

 

The issue according to the transmission shop is the TCC apply piston. GM designed this piston in steel, riding in an aluminum bore in the valve body. Expansion of steel and aluminum are very different, leading to interesting wear of the bore, leading either to a leaking TCC apply piston, or the piston sticks in the bore, leading to insufficient fluid pressure to maintain TCC lock. This leads to the PCM detecting the bad lock, and disabling further TCC lockup and overdrive until the next start cycle, and the setting of a P0740 code.

 

The transmission shop is saying there are two possible solutions, Sonnax makes a kit to allow the repair shop to drill out the bore, install a sleeve and new piston, or the valve body can be replaced. The shop is going to pull my transmission back out of the car, and fix (hopefully) the problem.

 

Part of what makes the diagnosis so difficult is that there are other possible reasons for TCC lock failures, from a misaligned shift switch, to a bad PWM solenoid, bad TCC brake switch, or even a bad torque converter. In my case, all of those have already been replaced during the rebuild, yet the issue remains; the transmission works perfectly until the transmission gets around 200 degrees Farenheit..

 

I'll keep everyone updated on which solution the shop takes, and whether it solves the issue.

Edited by Galaxie500XL

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please keep us posted. i have an otherwise good 130,000 miles tranny sitting in the garage that certainly could use this repair kit... that said, a source for the part and a write-up would be awesome!

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Just a quick update, I left the car at the transmission shop this morning. Played around with the car over the past week, confirmed with the transmission shop the shift solenoids, PWM solenoid, and torque converter were replaced during the rebuild. Driving around with my scantool connected, I got very consistent behavior. Transmission was perfect, as long as the transmission temp remained below 195 degrees Farenheit. Once that threshold was passed, DTC P0740 was set, the TCC no longer locked, disabling TCC lockup attempts, and overdrive until the car was shut off, and transmission temps fell below 195. The transmission shop said this is fairly common on the 4T60E, they had tried honing the bore a bit, which usually resolves the issue. The piston moves smoothly in the bore, but only at low temperatures. The shop said that in cases where lightly honing the bore did not solve the problem, either the Sonnax "Sure Cure" kit was used, or the valve body was replaced with a new one. In this case, they decided to replace the valve body under their warranty. Since this is the only change they are making to the transmission, it should be reasonably certain if valve body replacement fixes the problem, that's where the problem lies. Unfortunately, the "Sure Cure" kit itself runs around $160.00, and a special tool and jig are needed to use the kit. At that point, unless you're replacing dozens of these things, a new valve body is probably the least expensive way to go...if you call $250.00 for a valve body "least expensive".

Edited by Galaxie500XL

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I had issues with my damn brake switch sticking and ending up with no TCC lock. This only happened after driving the car for a bit as well. I unplugged the switch and all was well. (there are two brake switches, and all my lights still worked so I never dug into the operation of the other switch cause everything worked perfectly)

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You bring up a good point. There is a laundry list of issues that can cause no TCC lockup. My scantool has been absolutely invaluable in tracking down the issue, because I can see what the ECM is seeing--TCC duty cycle, TCC solenoid OFF or ON, TCC slip, TCC brake switch, and transmission temp. I chased down all of them before I committed to the transmission rebuild, even installed a factory trans cooler, because I really didn't want to spend money unnecessarily.

 

Always best to look for the simple stuff, like the brake switch, before spending lots of money. :thumbsup:

 

Unfortunately, in this case, a rebuild was the only remaining option, and even then the shop missed the underlying issue.

Edited by Galaxie500XL

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Well, final entry from me in the thread...

 

The transmission shop turned out to be run by a good guy...he had great reservations about pulling the transmission, replacing the valve body, and possibly still having a problem..

 

So, instead, he found another 4T60E, rebuilt it, and then had me bring my car in for a little over a day, and replaced the transmission completely.

 

Works perfectly!

 

I really would have preferred fixing the orignial. The shop owner did agree that the most likely culprit was the valve body, but preferred completely replacing the trans, rather than chancing a third go-round on his dime if the valve body didn't solve the problem.

 

The only thing I cared about was getting it fixed...and for $1300.00 for a rebuilt (and replaced) transmission, I'm happy...especially with the 26.9 MPG fuel economy I got yesterday. Previous best was 21.9...not too shabby for an LQ1, with 5 passengers~:)

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Thanks for the updates, epic beard man! (I'll admit I don't know your name, even though I looked for it.) In all seriousness, I'm having some strange issues out of my '95 Grand Prix coupe. Getting an SES light and no TCC lockup after driving for a little while, although I do have 4th gear. I don't have a scantool to check my trans temps, unfortunately. The previous owners beat the living hell out of this car, and a transmission spill and fill is likely in order here soon.

 

But anyway, this gives me a good basis to start from, so I wanted to say thanks. :D

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Actually, my name is Daniel, but Epic Beard Man is OK by me. I was a bit disappointed, I really wanted him to replace the valve body, to know ABSOLUTELY for sure that was what the issue was...but on the other hand, the shop DID make it right, without ripping me off.

 

Thanks for the updates, epic beard man! (I'll admit I don't know your name, even though I looked for it.) In all seriousness, I'm having some strange issues out of my '95 Grand Prix coupe. Getting an SES light and no TCC lockup after driving for a little while, although I do have 4th gear. I don't have a scantool to check my trans temps, unfortunately. The previous owners beat the living hell out of this car, and a transmission spill and fill is likely in order here soon.

 

But anyway, this gives me a good basis to start from, so I wanted to say thanks. :D

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Actually, my name is Daniel, but Epic Beard Man is OK by me. I was a bit disappointed, I really wanted him to replace the valve body, to know ABSOLUTELY for sure that was what the issue was...but on the other hand, the shop DID make it right, without ripping me off.

 

It's entirely possible that the 209k miles on this trans is causing it to act up too. I'll do a spill and fill here soon and see if that helps.

 

Can I ask you what kind of scantool you have that's compatible with OBD1.5?

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I have an old Actron CP-9110. I lucked up, it came with a GM cartridge. $50.00 bucks on EBay. I had actually bought it to work on my old LeBaron, and had no idea it had the GM cartridge and cable until it arrived.

 

Works through '95. I had no idea it would work on the '95 Cutlass, because I bought the scantool several years before I had the Cutlass. Like I said, I just got lucky. :thumbsup:

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