Alrighty, for starters this is on my 1995 g20, so it is not lt1, but a 5.7 tbi, either way it is era appropriate for the trans stuff. Thankyou ahead of time!


So, when i test drove the van, i got lockup. On my way home with it i dont get lockup. I have been driving it for a few weeks now and lockup has not come back even once.

It does not store any codes.

The SES light comes on at cruising speed but goes away, seems to not show up if i stick to backroads with lots of varied speed.

The trans works perfectly in every other way, shifts are smooth and solid, downshifts are perfectly time, etc, fluid looks great and is full.

Idle seems a bit high in park, i have not put a tach on it. coolant temp sensor to the PCM could be at fault, coolant is nasty, i need to flush it.

Harness looks really clean, actually the whole van is pretty darn immaculate all around. I did unplug the trans connector and it looked clean, and plugged it back in. Grounds are all clean.

Not sure what else to note.

I wonder if this could just be a brake switch issue, as i do not think that will throw the code. Do any of yall know if it is it integrated with the stop lamp switch, or shift lock, etc?

Perhaps this is an PCM fault, i should probably yank the tps or something and see if it holds a code. I am going to buy a backup used one anyway...


any input would be appreciated. Where would yall start looking?

When you say no codes stored, did you reach that conclusion by not having the ses light on? Or did you scan for codes? If you didn't scan for codes, do so. This is because there are codes that don't light the ses. But cause non lockup of tcc.

There are many things that can cause non lockup . 1st, the vehicle must meet certain conditions for lock up to engage. A factory service manual will tell you what conditions must be met to engage lock up.

2nd the brake switch does affect lock up. Some cars have 2 brake switches, and some cars have the brake lights and tcc interrupt built into 1 switch. You will have to consult the service manual to know which you have.

The tcc interrupt switch is a normally closed switch. This means there is power transferred through switch until you push on the brake pedal Then it releases lock up. If the switch is stuck on,, tcc will not engage.This switch communicates with pcm. When swich is open, pcm cuts ground to tcc.

On f-bodys, switch has both brake lights & tcc interrupt.

Other problems you may have include, no power to tcc. Power comes into trans on pink wire. It goes to 3-2 solenoid. It then is internally connected to tcc solenoid. You need to do a key on check of tcc to see if it has battery voltage. What makes tcc engage is that pcm provides the tcc ground on the white wire going into trans.

So if tccsolenoid gets no power, even when pcm supplies ground, tcc won't engage.

You can test tcc engagement by splicing a wire into the white tcc wire going to trans. Run the spliced in wire into passenger compartment. Attach wire to a switch. Attach another wire to other side of switch and run to a good ground.

You can test drive your car. Every time you turn on switch, tcc should engage. If it doesn't either tcc bad, no power to tcc, or converter clutch is toast.

Thankyou for helping me understand all that better, and i have an update.

...on the topic of lockup, i need to apalogize for a false alarm. i was completely incorrect, i must of felt it more initially because the thing sat for a long time before i test drove it, maybe pwm was stuck.

I have had 700r4s in the past that i felt it more too... It works! i think the PWM is just very effective. A tach would of solved it sooner.
It is near impossible to tell in OD counting for an extra shift does not work, but in D at 55 its definitely locked up, and if i hit the brake and then punch it i can feel and hear rpms go up with the TC slip and then feel that it is locked up in throttle response, engine braking etc.

after playing with it more it seems to only lockup over 40 or so... which seems about right.

...as an excuse, i have 3 noise kids under the age of 7 in this van at pretty much all times i am in it, which does not help in detecting anything but them lol.

The light coming on at cruise when i expected lockup made me paranoid, and i will be towing with this thing and did not want to overheat and destroy the trans.



When i mention it does not store a code, i mean that the SES light comes on, specifically at cruising speed, and when i scan it for codes i find nothing. When i shut it off and start it again the SES is off until i cruise at speed (usually 50-55) when it comes on again.

so the SES light is something else...

Again, thankyou for your response and sorry for the false alarm, i should probably make a new thread pertaining to the SES and have this one closed

Glad the problem was no problem.

If your going to use van as a tow vehicle, you should add on an aftermarket trans cooler. It will add many miles to your 4l60e's life.

The factory trans cooler located in radiator is a joke at best.

Me too!

thanks again, fortunately It has the HD cooling package and factory towing pack with the extra trans cooler already on it, though i have not measured its size compared to an after market one. Staying out of OD should help save it as well. Should tow well with the 3.73 gears that are in it. I have an LPW finned deep oil pan, sonnax super hold servo, as well as some other various sonnax parts to add to it. I plan to set up a temp gauge for it too.

Thanks for sharing, i have got a chevy towing truck we have to use for Nyc Blocked Driveway Towing Service, we have to buy another one which truck would you suggest ford or GMC?

We.re GM people on this forum. But Ford makes a tough truck also. Buying a new heavy duty truck is like a crap shoot. You roll the dice and hope you get a well built one.

If mrsmokey is still tuned into this thread, your ses problem with code not being stored in memory could be due to no key off power on one of the live power lines to pcm.