1993C4LT1

I know I can do the diagnostic, just need some help understanding the procedure. Don't want to take the car to a vette shop, and have them tell me it needs a new converter. Maybe that is the case, but I need to find out myself. Anyways, why am I wanting to do the diagnostic? Because the converter will lock, but doesn't stay locked when it should be. Aka, at cruise above 47 MPH.

Checked TPS at cruise, the number were not high. So not the TPS.
And yes, that was checked with the engine oil and coolant temps in the low 200s.

Page 6E3-C8-7 from the 93 FSM.
Step 1
"connect test light to DLC terminal "F" and ground"

OK, so simply ground the test light, and point the probe in terminal F on the ALDL?

Then it says the bulb should light. And if it does, "depress brake pedal. Light should go out. Does it?"

If NO: Then something with the brake switch is up.
If YES: "Ignition ON, engine off. Release brake pedal. Ground diagnostic terminal. Light should be off."

So i assume leave it grounded with the probe in terminal F?


Step 1, but this time following where it says "NO"

NO would mean that with the ALDL grounded in terminal F, that the test light didn't light up.

"Disconnect TCC electrical connector. Connect test light between terminal "A&D". Bulb should not light. Does it?

I don't get where it says: connect test light between terminal A&D. On what, the TCC connector or the ALDL?

If you get "NO"
"connect test light from terminal "A" to ground. bulb should light. does it?

Bulb does not light: Then the cause is a "open in ignition circuit TCC brake switch circuit or adjust switch."

If it does light: Ground DLC terminal "F". With test light connected between transmission connector terminals "A&D".

I don't get that last step at all.

If anyone can help me understand this diagnostic, that would be nice. Hate to take it to a shop and have them lie.

Kevova

any particular reason you are diagnosing TCC?

If test light lights - voltage is travelling through the fuse and the TCC brake switch to the ECM. Pressing Brake pedal would interrupt voltage to ECM and light would go out.

Following the "No" side You would check Fuse, then TCC brake switch adjustment. If TCC brake switch is properly adjusted and 12v still isn't on both sides when pedal is released switch has failed. If not then check for voltage at green / black wire at transmission connector
No there is an open circuit between TCC brake switch and connector. The manual sends you under car to jump green/black wire to tan and black wire to see if test light will light at ALDL.

I would rather check TCC brake switch before the hassle of climbing under car.

1993C4LT1

I understand that and thank you! What I don't understand is this.

"Disconnect TCC electrical connector. Connect test light between terminal "A&D". Bulb should not light. Does it?

I don't get where it says: connect test light between terminal A&D. On what, the TCC connector or the ALDL? And how do you connect a test light between two terminals? Makes no sense to me.

Kevova

Manual is written for techs who do this stuff for a living so they have all kinds of stuff to do testing. You can make a little jumper wire, a paper clip etc. and attach clamp to it.

If you monitor the aldl terminal f with a voltmeter you should be able to determine if ecm is turning off tcc or not.

With a voltmeter on terminal f you will have 12v until tcc engages and voltage should drop.
If it reads 0 no voltage to ecm to turn on TCC.
12v ecm turned tcc off. ecm or gear switch circuits
Voltage doesn't change hydrallic failure best case TCC solenoid....worse internal leakage and/or possible converter. ECM still has TCC commanded on, but TCC released on it's own.

Access to a scanner or data logger that will pick up transmission would be very handy because you could see all the input switches and the TCC command.

1993C4LT1

I indeed do have a scanner. Does this look like it will help?




I did use this to see if the ECM is telling the Torque converter to lock. And above 47 mph, it does tell me "yes". But it will read "yes" the whole time. Even at a stop light at idle. So I don't know how much I can trust/believe it.

WVZR-1

Look at 8A-20-2 and the A & D you're asking about is the connector @ the transmission. '93 has a 5 pin round vs 3 pin square transmission TCC connector.

1993C4LT1

Superb, thank you!

So even if the ECM is telling the TC to lock, if the the TCC solenoid is bad, the ECM will still say the TC is locked? Even though it isnt. Do I have that understood correctly?

I doubt the solenoid is bad because the problem is so consistent. But of course, I'm not going out without diagnosing it

aguilar92c4

Why are you diagnosing this Sir? and how do you know its not locked or is locked? I wouldnt trust that software you are using to diagnose it.

Kevova

If you watch tach you will see a change in rpm when tcc engages and releases. If the tcc releases while thr ecm has tcc commanded on. It's a hydraulic problem. The electrical part of solenoid can be on but valve doesn't move to turn on tcc.

JrRifleCoach

OK so there are two methods to accomplish the same outcome. 1. Yours, is to have instrumented proof. 2. drive the car on a nice straight section of road and while observing the tach, watch for the rpm drop after the 4th (OD) shift. Its about a 250rpm drop. To confirm the TQ lockup modulate the throttle slightly but to not cause the cars speed to change. You should not see the tach speed changing as the throttle is changing (TQ Locked). You can also try this at slower speeds in any of the lower gears, to observe the rpm change as the throttle position is changed. (TQ un-locked) As the TQ is spinning on the fluid.

Hope this helps.

1993C4LT1

When locked in OD, 3.07 gears, car should be 2k at 70 mph. It's completely evident the converter unlocks on me. I'm not crazy trust me At 70 with the converter unlocked, I'm probably doing around 2,300 rpm.

1993C4LT1

It does lock above 47 mph. You can hear it lock by the exhaust note, it changes like another shift almost. And of course, tach rpm drop. So it locks, but will unlock no matter what in about 10 miles or so of highway driving.

PatternDayTrader

Kinda sounds like a messed up tcc solenoid.

1993C4LT1

A part of me just wants to drop the pan and ohm test the solenoid. But knowing the converter does stay locked for a few miles, it might ohm out OK. I'm confused

PatternDayTrader

You can do that through the connector. Its a good idea actually. Get the car warmed up and into the failed state, then test. I would just replace the solenoid if you are going to pull the pan. Its not an expensive part.

Mike Holmen

I run a manual lock-up switch on mine, way easier than trying figure out what the computer wants. Lots of TCC kits out there to do what I've done. I made my own kit.

I have mine set-up to disengage when I press the brakes. I also have a lighted switch on my dash to tell me the TCC is locked up or not.

1993C4LT1

So I asked the local Chevy dealer I always buy parts from. Told them I need a Torque converter clutch solenoid for a 93 vette. They told me they are "discontinued". I highly doubt it, since many cars used the 700r4/4l60/4l60e trans. Did I name the part wrong or? I say screw it, I'm just gonna drop the pan and do it, as soon as I get the solenoid. I changed the fluid and filter back in April of 2017. Should I buy a new filter, or keep the one I have in there? Put about 3k miles since.

WVZR-1

He could very well be correct but using an old GM SPO publication here you want to be shopping for a 10478114 - you could ask the dealer if that's correct and then do the usual sources to see what you find.

I think if I were you I'd also do the DIC diagnostics for the ECM, ASR/ABS from the FSM.

I thought of you when I posted the diagnostics earlier today.

I'm not a big fan of ALDLdroid or any of that stuff maybe because I've never attempted to compare it to Tech1 or Tech2 results.

The solenoid with wiring would be a '92 - '93 only thing.

Maybe the aftermarket does the TCC less harness and you could cut/splice but I'd maybe want the OE if I could find. Ask the dealer if he could maybe locate you one.

1993C4LT1

I didn't know the ECM would throw a code for a TC lockup problem? But hey, I have been known to be wrong. I can easily scan codes, not a problem.


Looking at a pic of that part number. I thought it was just a solenoid you simply unscrew. But it looks like a wiring harness as well. Would I just unplug the connectors, and plug the new stuff in? Forgive me if I sound novice.

WVZR-1

The reason I mentioned doing the codes is I believe a code 28 was very early identified as a transmissions pressure issue, later I believe it's only referenced as a Quad Driver failure or issue. It costs nothing to do the diagnostics so why not.

How did you actually do with the FSM diagnostic charts?

Can you buy a solenoid in the after-market and accomplish a cut/splice? I have no idea.

Did the dealer confirm the part# for you? He should remember you and you buy there so I wouldn't be reluctant to make the call.

It seems you understand the install - maybe a pressure switch issue? Maybe Arbee will check in if he sees the thread.