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I just bought a 44k mile 1985 z28 305 with TPI, lb9 mostly all original the trans was rebuilt in 2003. The Tcc was not applying, i hooked up a scan tool and the Shan tool reads Tcc locked: yes. Unless I hit the brake.. But this is at idle in park in the driveway. I looked under the car to see the connector hanging.. I plugged it in went for a ride and she slams and locks every gear unless I ever so slightly touch the brake pedal then it's normal and the Tcc never applies. The wiring is emaculate. There's no messy wiring. Very clean car. Is there anything anyone could direct me towards for a fix? I don't want to run wires and make my own switch. I'd like it to be right. Thanks guys!
Re: Tcc applied all the time unless brake applied?
The connector is receiving signal to lock up all the time except when hitting the brakes. When it hits second gear it's already locked up. It's hellacious to test as the link above describes to test. I have a working Tcc system. But something is signaling on. Maybe a bad driver in the ECM? Or is there anything else?
Re: Tcc applied all the time unless brake applied?
Originally Posted by 88_SportCoupe
I just bought a 44k mile 1985 z28 305 with TPI, lb9 mostly all original the trans was rebuilt in 2003. The Tcc was not applying, i hooked up a scan tool and the Shan tool reads Tcc locked: yes. Unless I hit the brake.. But this is at idle in park in the driveway. I looked under the car to see the connector hanging.. I plugged it in went for a ride and she slams and locks every gear unless I ever so slightly touch the brake pedal then it's normal and the Tcc never applies. The wiring is emaculate. There's no messy wiring. Very clean car. Is there anything anyone could direct me towards for a fix? I don't want to run wires and make my own switch. I'd like it to be right. Thanks guys!
I looked at the schematic for your car hosted at austinthirdgen.com and saw that the solenoid gets a constant source of +12V and it's the negative side of the circuit that the ECM completes to allow lockup . The +12V power feed is from the fuse labeled "Gauges" and feeds a pink/black wire to the brake pedal N/C switch . It leaves that switch as a purple wire that feeds right to the + side of the solenoid (through a connector or two , of course . The Tan/Black wire coming back from the solenoid is the one that the ECM switches to ground when lockup is commanded . Of note is that the Tan/Black wire also is connected to a pin of the ALDL . From your description of the problem the two things that come to mind are a short to ground in that Tan/Black wire or a defective ECM (solenoid driver transistor internally shorted to ground) . Were this mine to diagnose I think I'd disconnect that Tan/Black wire at the ECM and if the problem goes away it's the ECM and if it persists with it disconnected from the ECM I'd look for a short somewhere in that wire's run .
Re: Tcc applied all the time unless brake applied?
PS , the wire colors I gave you are for the wires external to the transmission . The actual solenoid itself in the transmission , after the connector that brings the power through the transmission case , has a red wire on the purple (+) side and a black wire on the Tan/black (switched -) side .
The ECM terminal that the Tan/Black connects to is listed as "C1 A7"
PS , Don't forget there is a so called "top gear switch" that feeds a grounded or not signal to the ECM on pin "C2 C18" VIA a dark green wire . I know the ECM uses this switch along with other things such as road speed to determine when to lock up the converter . What I'm NOT sure of is what the ECM would do if that switch were to be defective and "telling" the ECM that the car is in top gear when it actually isn't . My presumption would be that it shouldn't lock the converter full time , but sometimes replaced electronics can do strange things in 30 year old cars . Maybe start by disconnecting that first and see if the constant lockup stops , and if not then unhook the Tan/Black and retest .
As with you also , my sneaking suspicion is the ECM , but the tests of disconnecting those two wires should prove that one way or the other ....
Last edited by OrangeBird; 03-23-2016 at 04:42 PM.
Re: Tcc applied all the time unless brake applied?
Originally Posted by Bob88GTA
That's a pretty good explaination OrangeBird! I'm with you on ths.
Thank You Bob . I'm just SUPER happy we have the schematics for our cars available to us so handily . My other car , of a different manufacturer , they keep tight hold on the wiring diagrams and I've never been to happy with them for it .
Re: Tcc applied all the time unless brake applied?
1986 tpi has 18 pin, I have a 85 with 6870 ecu, found a pinout, a7 is Tcc request. I don't see a top gear, but 4th a/t or 1st m/t I wonder if that's it?
Re: Tcc applied all the time unless brake applied?
Then everything follows suit with the pinout but two wires, c8 and c9
C-8 at 4th gear blue (mines green)
C9 fan control green (mines blue)
Are they switched accidentally? This is a divorced car in which the wife won it. It could be fd up, maybe the reasons for a replaced ecu and transmission? The fan works though. With or without a/c I'm stumped, scared to swap the wires as the pinout label describes....... Maybe the pinout is wrong?
Re: Tcc applied all the time unless brake applied?
Originally Posted by 88_SportCoupe
1986 tpi has 18 pin, I have a 85 with 6870 ecu, found a pinout, a7 is Tcc request. I don't see a top gear, but 4th a/t or 1st m/t I wonder if that's it?
Yes Sir , I have seen it called "4th gear switch" also , so that's likely it .
Now that you know disconnecting C1 A7 stops the undesired lockup , if it still locks continually with the 4th gear switch disconnected (and of course the Grey/Black C1 A7 reconnected) we can call it a bad ECM .
It's likely that with the ECM totally unplugged from the harness , that C1 A7 terminal will show a hard short to the ECM's ground pins using an Ohm meter . C2 D3 (for sure) and what looks like C2 D6 (or is it 8 ?) are two that are listed as ECM ground terminals .
Last edited by OrangeBird; 03-23-2016 at 05:47 PM.
Re: Tcc applied all the time unless brake applied?
Orange bird, please see this, you were probably thinking and replying as i updated the status...
Originally Posted by 88_SportCoupe
Then everything follows suit with the pinout but two wires, c8 and c9
C-8 at 4th gear blue (mines green)
C9 fan control green (mines blue)
Are they switched accidentally? This is a divorced car in which the wife won it. It could be fd up, maybe the reasons for a replaced ecu and transmission? The fan works though. With or without a/c I'm stumped, scared to swap the wires as the pinout label describes....... Maybe the pinout is wrong?
Re: Tcc applied all the time unless brake applied?
Originally Posted by 88_SportCoupe
Then everything follows suit with the pinout but two wires, c8 and c9
C-8 at 4th gear blue (mines green)
C9 fan control green (mines blue)
Are they switched accidentally? This is a divorced car in which the wife won it. It could be fd up, maybe the reasons for a replaced ecu and transmission? The fan works though. With or without a/c I'm stumped, scared to swap the wires as the pinout label describes....... Maybe the pinout is wrong?
Give me a minute to have a look at the diagram for C8 and C9 ...
Interesting , my diagram shows the fan control as being C3 E8 and a dark green / white wire , and the 4th gear being C2 C? (either 16 or 18 , can't read the inkblob) and a dark green wire , so now I don't know what to make of the discrepency between the schematics . I'm using the Austin third gen schematics , where are your schematics from ?
Last edited by OrangeBird; 03-23-2016 at 05:58 PM.
Re: Tcc applied all the time unless brake applied?
Originally Posted by 88_SportCoupe
Austins doesn't have 1985 305 EFI and 1986 is a different ecu and different pins all together
When I look at the schematic I was looking at , I see your correct that they don't have the exact one you need . I'm glad at least the lockup command at C1 A7 is the same , but I have no other source to look for '85 305 EFI .
I really should learn to put my darned reading glasses on before looking at this stuff .
Re: Tcc applied all the time unless brake applied?
This should help,... It's from the 85 shop manual.
Make sure everything is connected as it should be and that there are no alterations to the factory wiring ( like when people tap into Pink/Black to get power at the brake switch,..... or wire a manual TCC lock-up at the ALDL ) Once you know everything is as it should be, only then start probing wires to figure out what works and what doesn't.
It's easy to check the power side,... it's always 'on' unless the brake is pushed, but checking the negative side is a bit more tricky. ( The TCC Switched Ground wire = Pin "F" on your ALDL. ) You can wire a test light to power on one side and to ALDL Pin 'F' on the other side, then take a ride. If the light turns on then the ECM is sending switched ground, so you know the computer is working. If the test-light doesn't ever come on, ( suspect = ECM ) wire a toggle switch to ground and to ALDL Pin 'F' and take another ride....... Flip the switch at 45 MPH and see if the light - and TCC - works.
P.S. Don't use a Scan tool for this !
Last edited by John in RI; 03-23-2016 at 06:55 PM.
Reason: P.S.
Re: Tcc applied all the time unless brake applied?
Thank You John , Nice diagram !
So it seems all is the same regarding wiring colors and the ECM pinout for the solenoid itself as with the diagram I was looking at , and it's only the 4th switch that's different . The bottom line was when 88 sportcoup unhooked the solenoid wire from C1 A7 the always engaged solenoid disengaged . So clearly the ECM is commanding the lockup when it's not proper for it to be doing so . Now all he needs to do is figure out why the ECM is full time grounding that pin .
Re: Tcc applied all the time unless brake applied?
Thank you both. I do apprietiate your time and efforts. Helping me with this headache. My next day off is Sunday. I'll hook my scan too to recheck data. I do remember it saying Tcc lockup -yes when in park. I wonder if it's the ECM itself that's keeping it "on".....
Re: Tcc applied all the time unless brake applied?
Originally Posted by 88_SportCoupe
Thank you both. I do apprietiate your time and efforts. Helping me with this headache. My next day off is Sunday. I'll hook my scan too to recheck data. I do remember it saying Tcc lockup -yes when in park. I wonder if it's the ECM itself that's keeping it "on".....
Glad to help and yea , my suspicion is still that the C1 A7 pin's driver transistor has gone hard short to ground in the ECM itself . Keep us posted on what ya find when you get back into it on Sunday .
Re: Tcc applied all the time unless brake applied?
So I can't wait. The scan tool says 4th yes at 0 speed, also during driving in manual 3rd, it says no. The info doesn't change. I waited a few seconds, about 30...... No change in yes or no. The speedo is cable and is exactly what the computer says.
Re: Tcc applied all the time unless brake applied?
Okay so, with the Tcc wire unplugged from the ecu and the 4th gear switch wire unhooked from the ecu, the scan tool continues to say "yes". The local parts store has a 6870 in stock. I know I should upgrade the ecu but. Not today. Lol I'll do that tmrw and I hope it says no no no no in park at idle.....
Re: Tcc applied all the time unless brake applied?
If the TCC lock-up was actually engaged all the time,.... the car would stall out HARD as soon as you put it in 1st gear.
I don't get it; I don't understand how a scanner can tell you much about the TCC & I'm thinking the scanner is lying to you.
The Tcc was not applying, i hooked up a scan tool and the Shan tool reads Tcc locked: yes. Unless I hit the brake.. But this is at idle in park in the driveway. I looked under the car to see the connector hanging..
This is your initial post; under that scenario; TCC would never engage because it is unplugged ! If the connector was hanging TCC was NOT engaged. no Matter WHAT your scanner says. If the tranny is not plugged in then no power - or switched ground - is getting to the solenoid.
4th gear switch is INSIDE the tranny and connects only to the ECM. If the tranny plug is disconnected the 4th gear switch in the tranny - obviously - can't communicate with the ECM. So how exactly is this scanner reading 4th gear ??
Ditch the scanner and start over.
Hook-up/connect everything AS IT SHOULD BE !!
Get a spare light bulb/socket and connect 1 side to power, connect the other side to PIN 'F' on the ALDL and start the car.
Light Off; NO TCC,... Light on, TCC enabled.
Drive the car up to 50 MPH and watch for the light to turn on, when the light turns on,... TCC is enabled by the ECM. If the light never come on,.. ECM or wiring is bad.
Re: Tcc applied all the time unless brake applied?
Tps was at .70 after countless researching I found .54 is optimum. So I reset it and reset the computer rechecked. No difference, scan tool reads .54, no glitches in the slow sweep.
Re: Tcc applied all the time unless brake applied?
Okay, plugged it in reinstalled everything. Scan tool finally says 4th NO. Test drive, Tcc didn't engage until 3rd and it felt like it went from 3rd to 3rd locked/4th locked bogged right down to 800rpm at 20mph. I pulled the shifter to manual 3rd it picked right back up and was fine. So i suppose if I use 4th for over 50 I'll be fine......... But it still makes me wonder why does it now go from 2nd to almost immediately 4th. Kinda odd. Maybe I should order a new transmission and be done with this horror show.
Re: Tcc applied all the time unless brake applied?
OK. I'll put my e cents in. Set your TV cable toprevent "shot shifting". Push the tab in on the TV cable, pull cable all the way. Back, get in the car and press gas pedal to the floor. TV cable is now set. HTH's
03-23-2016, 11:07 AM
When I look at the schematic I was looking at , I see your correct that they don't have the exact one you need . I'm glad at least the lockup command at C1 A7 is the same , but I have no other source to look for '85 305 EFI . 
I really should learn to put my darned reading glasses on before looking at this stuff . 
