My 88 Formula suffered the usual auto-trans lock-up problem about two years ago. I ran the car for a while with the TCC solenoid disconnected. Then thanks to some excellent how-to write ups on the forum and elsewhere, I managed to replace the solenoid and the third-gear switch, cleaned out the transmission end cover and put it all back together.
I drove the car all through last summer (it's not my daily driver, but I use it in the good weather). The lock-up worked perfectly, engaging when the transmission was warm and once my speed got up to around 50mph, and disengaging perfectly when I tapped the brake or slowed down.
I've had the car in the garage for the last three months over the winter, and have just resumed using it. It runs OK (although the idle-speed seems higher than it used to be, at around 1200rpm - that's a separate issue I need to explore). But I notice that the lock up is now not working. It just doesn't engage. I have checked the connection and sprayed it with dielectric grease (it seems to be good). What else might be causing the lock-up not to work? I don't much like the idea of having to re-open the transmission cover just to look inside and wiggle the internal connections, but I don't know what else I can do to check and/or re-activate it.
Of course in the wider scheme of things I can still run the car with no lock-up - it will just mean heavier fuel consumption - and that's less of a headache than having a lock-up which won't dis-engage. But I would like to get it working normally again if I can...
Some of this may sound stupid. Do the brake lights work? Switch sticking? T125 should have 12v, key on, brake off at the TTC power terminal and 0 when brake applied. Can check that with test light. And with the connector disconnected from the transmission. Reconnect the connector and check for voltage at the TCC command terminal(key on engine off)(Back probed). This will tell you if you have an open inside the trans. It should have 12v untill the ECM apllies ground to TCC command terminal. Key on engine off, find the TCC command terminal again and back probe(paper clip works great), ground the command terminal and you should hear the TCC solenoid "click". If you picked the wrong one you will blow the gauge/TCC fuse. This will tell you if the TCC solenoid is sticking open. Rule of thumb. Never apply battery voltage to anything connected to the ECM unless directed by a diag flow chart.
Beyond that you need to see if there is something keeping the ECM from commanding lock up. Too low/high TPS, Too low/high map, Too cool coolant, open coolant sensor. those will also cause it not to go into closed loop. There is a preset temp it has to reach before it will command TCC. Third gear switch stuck open in trans or broken wire. These are much, much easier to diag with a scanner or win ALDL. You can watch all and watch for TCC command.
[This message has been edited by cmechmann (edited 03-01-2014).]
Does the car get up to temp? Is the thermostat closing? Temp sensors okay?
My thoughts exactly.
I've had cars where the TCC wouldn't lockup, or if it did, it was only while driving around town fully warmed up. Hit the highway and it would promptly unlock and the RPMs would jump.
Thanks for those replies - all helpful in pointing out what to check.
I have WinALDL loaded on to an old laptop, and I have a cable-connector.... but haven't yet tried it out. Maybe the moment has come? Incidentally, I did check the "Service Engine Soon" codes in the old-fashioned way with a jumper-wire, and no fault codes showed up. So I am assuming that none of the engine sensors is registering anything seriously out of whack.
Having said that, the car has always run ridiculously cool considering it is mid-engined. Except in serious urban traffic, the temp gauge scarcely moves above the first two or three marks on the gauge. I had always been secretly grateful for this (I have another car that is very prone to overheating, which is a constant worry). And the fact is that for many years the lock up worked even thought the engine always seemed to be running cool; and it worked again immediately after I replaced the solenoid and third gear switch some 18 months ago.
As for all the advice in cmechmann's post, none of it sounds stupid. In fact some of it is a bit too expert for someone with as little electrical/electronic skill as me. First off, yes, the brake lights do work. I don't think the switch is sticking (but if it did, would that not prevent the TCC lock-up from DISengaging? Or is that too simple an assumption?) The warning about the risks of testing the wrong ECM connection and blowing fuses make me cautious. I will have to figure out which is the TCC command terminal (is that the same as the TCC power terminal?), where T125 is, and exactly where to stick the paper-clip!
I would have to dig up a schematic for the wire colors. But there should be a square 4 terminal connector front side of transmission just behind bell housing. This has the TCC power, TCC command from ECM, Sensor ground for 3rd gear switch and 3rd gear signal to ECM. The schematic I have is for a 1985. It shows TCC command as tan/black and TCC power as purple. You would be putting the paper clip beside the wire through the weather pack into the connector. Some years only had 3 wires and the 3rd gear switch was grounded internally. The brake light switch applies power to lights when depressed. Cuts power to TCC when depressed. The ECM completes the circuit by completing the ground side. When you let off the brake it cuts power to the lights and applies power to the TCC. You can also get the TCC command signal at the ALDL connector. It would be the opposite side of where you short to get codes. So if you short by connecting the last 2 terminals to the right, it would be the terminal all the way to the left. The last prom data that I had seen YEARS ago shown engine temp over 140F before TCC lock up. That was on an 85 Camaro. It would go in and out of lock up on highway from a stuck open thermostat.
[This message has been edited by cmechmann (edited 03-02-2014).]
Have just checked on the wiring and connections to the TCC solenoid.
Yes, there is a square 4-terminal connector (it's the one I unplugged when running without the lock-up before I replaced the solenoid). But it appears to have only TWO wires leading into it. One is purple, comes from the brake switch and goes into the "A" terminal. The other is tan/black, comes from the ECM, and goes into the "D" terminal. This suggests that the other two terminals in the connector ("B" and "C") are not used. Indeed iirc, there were only two wires leading from the solenoid inside the transmission to the female side of that connectors (and it was a pita to get them connected!).
So if I understand the earlier posts correctly, the first test is with the connector unplugged, and ignition on, there should be 12v power coming from the brake switch (purple wire); and then depressing the brake pedal cuts the power to give a zero reading?
Then with that connector plugged in, and ignition on but engine cold and not running, a backprobe of the ECM wire (tan/black, terminal D) should also show 12v?
Originally posted by cmechmann: The last prom data that I had seen YEARS ago shown engine temp over 140F before TCC lock up. That was on an 85 Camaro. It would go in and out of lock up on highway from a stuck open thermostat.
I just checked the data for an 88 auto, and the TCC lockup coolant temp threshold is set to 64.25C = 148F. Federal/CA are set the same.
br1an - if you already have the cable then it might be worth seeing what coolant temperature your ECM is seeing. If it's not hitting that threshold, it won't lock the TCC. Also, WinALDL will show if the ECM is attempting to lock the TCC. It's listed in the "flag data" tab at lower right.
Thanks armos.... I'm planning to start with the connectivity checks which cmechmann suggested. Then I'll hook up the WinALDL - which I have never used before - and see how it works. I will certainly need help in interpreting whatever readings the WinALDL produces, as the numbers won't mean very much to me!
Yep. Having 12v when you check with it connected tells you if you have an open in the TCC solenoid or the wiring in the trans. Most of the data/numbers that come up in WinALDL/or a scanner will make since from the start. Coolant temp, RPM, Air temp etc. May also show battery volts and other stuff like start time(how long since started) Closed loop/Open loop. Brake switch on/off. Most of the other sensors readings will be low than go high. example: Throttle position at idle will be around .6v then as you step in it will increase. Wide open being over 4.0v You'll get it. Once you see scan data, you will try to find all your problems that way. It does show you a lot. And after you get used to it and what readings to expect. But nothing replaces, physical test. Watched too many guys replacing MAP sensors from the scanner readings, then finding out they had a hole in the $2.00 vacuum hose. Replace a $200.00 MAF sensor and then find rats were munching on the wires.
Latest update on the physical checks on my TCC solenoid connection...
With the square 4-terminal plug by the transmission disconnected, and ignition on, I get 12v at the terminal (A) with the purple wire from the brake switch.
When I depress the brake pedal (and brake lights illuminate) the voltage at that terminal drops to zero.
So I conclude that the brake switch and wiring to the TCC is good.
Now.... with the plug reconnected, and a paper-clip inserted into the back of the other terminal (D) with the tan/black wire from the ECM. Ignition on, zero (0v). Ignition off, zero (0v).
According to cmechmann's first post above, "It should have 12v until the ECM applies ground to TCC command terminal." Now I'm supposing that, with engine stone cold and not running, the ECM isn't telling the TCC solenoid to do anything.
I know this may seem an obvious or dumb question, but I'm trying to be logical here. Should I be getting 12v - rather than zero - at that back-probed terminal when the ignition is on?
As I'm getting a zero reading, maybe this just means that the pesky paper-clip isn't making a proper contact inside the back of the connector. Or... does it mean that there is a problem (bad connection or fault) with the TCC solenoid or third-gear switch inside the transmission casing?
This schematic is from an 87 V6. I'm only assuming 88 is probably the same.
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Originally posted by br1anstorm: With the square 4-terminal plug by the transmission disconnected, and ignition on, I get 12v at the terminal (A) with the purple wire from the brake switch. When I depress the brake pedal (and brake lights illuminate) the voltage at that terminal drops to zero. So I conclude that the brake switch and wiring to the TCC is good.
Agreed - that matches the schematic. Positive voltage comes through the 'gages' fuse, through the brake switch, and to pin A at the TCC solenoid.
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Now.... with the plug reconnected, and a paper-clip inserted into the back of the other terminal (D) with the tan/black wire from the ECM. Ignition on, zero (0v). Ignition off, zero (0v).
the ground return goes through the third gear switch, then to pin D, then it branches to the ALDL-F and the ECM. The circuit is open at the third gear switch. The ECM should also be open, since it hasn't met the conditions to close it. So pin D should be floating in the conditions you tested. It should always have continuity to pin F at the ALDL connector though, if the wiring is intact.
If the ECM is commanding the circuit to close, then there's a problem in the circuit. If it's not commanding it, then the circuit isn't the reason. It will command even if the connector isn't plugged in.
[This message has been edited by armos (edited 03-05-2014).]
Sorry to mislead you I only had schematic for 85 which doesn't show the wiring in the trans. You won't be able to check 3rd gear switch unless you can connect something to the connectors while driving to get it in 3rd gear. We used to do it on a lift with wheels up. And that way was sketchy. Would not recondmend trying on jack stands. You next best approach is to see if the ECM is commanding it with WinALDL. If it is you are going to have to take the side cover off.
Thanks to armos and cmechmann - I think I am beginning to understand the mysteries of electricity....!
Armos - you say "pin D should be floating in the conditions you tested". By "floating" I presume you mean registering zero, not 12v?
As I read the wiring diagram, the power coming in to pin A from the brake switch does nothing unless/until (a) the 3rd gear switch closes and also (b) the "switch" inside the ECM closes, thus completing the circuit to ground and energising the solenoid to lock up the transmission. Then of course when you touch the brake pedal it cuts the power supply so the solenoid clicks off.
All of which - if I'm right - suggests that the only way to test whether the ECM is sending the right signal is to get the temp and speed up to the point at which the ECM is programmed to close its switch to complete the circuit, and the third gear switch is also closed. I shan't try that by running in gear on axle stands! WinALDL looks like the only other way to test.
That said, I have been looking again at the diagram again .... I presume that with ignition on, and thus power via the brake switch to pin A, there is no point in trying to ground pin F at the ALDL terminal as a way of energising the solenoid (=making it click), because it won't or can't do so unless and until the third gear switch closes too. What actually makes the third gear switch close - fluid pressure or something when the the auto box is up into third gear?
Or.... will connecting pin F of the ALDL terminal to ground make the third gear switch close too and thus complete the circuit and activate the solenoid?
..... which is what I suspected when I wondered in my post above, "What actually makes the third gear switch close - fluid pressure or something when the the auto box is up into third gear?".
