97 Blazer 4X4 ECT problem

[JURB6006]

Hi;

Code said TCC or circuit. The original TCC solenoid was found with crumbling
electrical connections. Ran good for one night after it was replaced.

The only way it can know for sure if the TCC is bad or not engaging is to
compare the VSS to the crank sensor.

If someone could confirm or deny this I'd appreciate it, when it threw the code
and started taking off in second, with passing gear disabled, this is a "limp
home" mode, correct ? I ask because it's showing exactly the same symptom.

What is the likelyhood that it needs a torque convertor clutch ? I'll mess with
valve bodies and bands, even pumps, but I will not take a torque converter
apart, even for my Mother. The rebuilt is $360 I guess and we got guys to put
it in.

Also, what else to check before taking the plunge.

Thanks in advance for any help.

JURB

 

[Bob Urz]

Hi;

Code said TCC or circuit. The original TCC solenoid was found with crumbling
electrical connections. Ran good for one night after it was replaced.

The only way it can know for sure if the TCC is bad or not engaging is to
compare the VSS to the crank sensor.

If someone could confirm or deny this I'd appreciate it, when it threw the code
and started taking off in second, with passing gear disabled, this is a "limp
home" mode, correct ? I ask because it's showing exactly the same symptom.

What is the likelyhood that it needs a torque convertor clutch ? I'll mess with
valve bodies and bands, even pumps, but I will not take a torque converter
apart, even for my Mother. The rebuilt is $360 I guess and we got guys to put
it in.

Also, what else to check before taking the plunge.

Thanks in advance for any help.

JURB

ah, what do you have? The notorious P1870 code?
I have similar problems with mine when its hot on the hiway.
Otherwise, its fine. What i have discovered is that the valve body
wear is causing problems. The valve hangs up in the valve bore and
the TCC does not fully lock up.

New valve bodies are pretty expensive. A company called Sonax makes kits
and valves to repair the valve body without changing it. There is a
special reamer and a updated valve to salvage the body.

You might check it out. I have been trying to figure out if i can take
the body off and repair mine with the trannie still in the truck. I take
it you have a 4l60E? If its gone too long slipping, you may need a
rebuilt torque convertor also.

Bob

 

[JURB6006]

What i have discovered is that the valve body

wear is causing problems

Thanks for the info, but I hope you're wrong. I understand that clutches don't
like it when they are anything but completely engaged or disengaged.

Thing is, like I said the electrical connector wasn't in too good of shape and
I'm hoping the A. we don't have the valve body problem and B that doesn't need
a torque convertor. One hopeful sign, I believe is here <a
href="http://member.aol.com/JURB6006/trans01.jpg>Picture of connector piece
(click here)</a> Now the way I see it an intermittent connection could cause
it, but the pins are clean, and it doesn't look like it is supposed to switch
to a lower holding current, so why the burnt area ? My guess is the connection
started going bad, then heat from that caused it.

Could the coil have shorted turns ? if so I might need to try to find the
transistor in the computer that drives it, it may be bad, thermally.

While I'm hoping for the best, I want to be ready for the worst. Thanks for the
info on the valve body, and if the torque convertor winds up getting replace I
see to it that this is looked into, don't want to burn up another one.

Do you happen to know how to check for sure if it has the problem with the
valve body ? We have micrometers and all kinds of machinist tools and measuring
instruments, and know how to use them. Is there a telltale step in the bore or
is it just wear with a smaller section of the valve piston cocking ?

Thanks again, for now I'm still on it.

JURB

 

[JURB6006]

Sorry;

<a href="http://members.aol.com/JURB6006/trans01.jpg">This is the good link.</a
href>

JURB

 

[Bob Urz]

Sorry;

<a href="http://members.aol.com/JURB6006/trans01.jpg">This is the good link.</a
href>

JURB

http://www.transmissionspecialty.com/parts/parts/77754-Combo.htm
http://www.transmissionspecialty.com/parts/parts/77805.htm
http://www.transmissionspecialty.com/parts/parts/77754-09K.htm
http://www.transmissionspecialty.com/tech_all.htm


Bob

 

[JURB6006]

HI, and thanks for the input;

So far so good, but now the question becomes, is there a definitive way to see
if this valve body has that problem ?

Feeler guage ? The thing is, being prepared for the worst but hoping for the
best I can now see the possibility that the valve body is defective, and the if
a new torque convertor is installed this problem could definitely cause it's
premature failure.

For now we can't tell whether the TCC is really fried or if it's an apply
problem.

Also I have some additional info, the actual codes are (P) 740, 753 and 785.
With any luck, this might shed some light maybe ?

This is one fault (I THINK), and to have three codes. . . . The problem is I
don't have a model specific book for this, up until now I've only been told the
descriptions for the codes. Of course one will be TCC or circuit, and then I
suspect one of them will be tranny fluid temperature, but what about the other
one ?

Incidentally I did check the web resources pointed out, they were quite
informative, except for one thing. How to tell if this is the problem. Hell it
could be the computer, but to find that out I'd have to reset it and make it go
to where it locks the TCC. Whether the solenoid is driven is one piece of info.

You may have seen the burnt connector, what if the coil had shorted turns ? If
so I might need a transistor in the computer. Are these things even marginally
servicable or am I going to be looking at an encapsulated assembly ? (like an
old tripler in a TV)

It would be a real (_|_) kicker to do all this torque convertor and shit and
find out all I needed was an ECG375. While I can check a wire for high or low
state, I doubt there is a pressure tap for this particular mode. However, does
the signal, or maybe line pressure drop when it tries to apply ? Anyone know ?

Thank you all again for everything so far,and thanks in advance for whatever
comes next. The main thing to me is that I don't want to burn up a new torque
convertor.

JURB

 

[BOB URZ]

HI, and thanks for the input;

So far so good, but now the question becomes, is there a definitive way to see
if this valve body has that problem ?

Feeler guage ? The thing is, being prepared for the worst but hoping for the
best I can now see the possibility that the valve body is defective, and the if
a new torque convertor is installed this problem could definitely cause it's
premature failure.

For now we can't tell whether the TCC is really fried or if it's an apply
problem.

Also I have some additional info, the actual codes are

(P) 740, tcc enable solenoid.

753 1-2 shift solenoid valve

785. 3-2 shift solenoid

With multiple codes for solenoid problems, i would be looking at
a plug or wire harness problem first. Did you unhook the transmission
harness plug and inspect the pins? Maybe unhook the PCM main connector and inspect,
clean and put back together? Any grounds
around the connector?

A google search will give you the code descriptions. But i fear
you will need t factory shop manual to know more. Look on ebay.
That's where i get mine. If you had a terminal problem on one solenoid, perhaps it
overheated the connector pins or if its shorted, its drawing too much current and
upsetting others. Do all the solenoids measure the same reading?

Bob

 

[JURB6006]

Thanks again Bob, but how did you get the meaning of those codes off Google ? I
just tried it and pretty much didn't get crap.

I got all kinds of things, but nothing that defined the codes.

Anyway, now I'm somewhat at a loss for specifics. How the heck would it know
about other shift solenoids, as well as the TCC one ? The codes, 1-2 shift, 3-2
shift and TCC, all at the same time ?

Now the question becomes how are they detecting these faults, are there
mechanical state switches in the tranny or is this all coming from an error
comparing the crank to the VSS, which incedentally I wonder exactly how they
deal with that, being a 4WD. I guess they would need a secondary VSS on the
transfer case output for the speedo, or does it just "know" ?

With these codes now, remembering the symptom:

Reset computer runs fine, afterwhile starts taking off in second and no passing
gear. When it gets hotter it will no longer shift into first even manually.

I wonder if the computer is reading the other two codes because of being in the
limp home mode. Even so, how could it differentiate between anything involved
at times when the TCC should be applied. When the TCC isn't applied how would
it know the stall rate of the torque convertor ? Is their math that good that
they can do it from the MAP or MAF along with the other engine values ? That's
almost scary (lol).

I say fairly assuredly that the TCC should not be applied in anything but high
gear, wouldn't you agree ? There is one possible fact not known yet,,,,,,,,, is
it POSSIBLE that the TCC is supposed to engage in every gear because they used
a bit of a different design of convertor, like one with nice high stall, but
need the TCC because it'll overheat ?????

This comes up because now I remember that the thing was picked up out of town
and during the trip it pushed out some fluid. It had to have been overfilled
because it wasn't real low when it got home. I wasn't on the trip, but I heard
there was quite a bit. Was it expansion, or maybe the torque convertor started
cavitating ?

A penny for your thoughts, hell I'll double it !

Thanks again

JURB

 

[Bob Urz]

Thanks again Bob, but how did you get the meaning of those codes off Google ? I
just tried it and pretty much didn't get crap.

Try the search phrase "DCT P0740"
that should pull up this page among others:
http://www.c5forum.com/ayc/1997dtc.php

I got all kinds of things, but nothing that defined the codes.

Anyway, now I'm somewhat at a loss for specifics. How the heck would it know
about other shift solenoids, as well as the TCC one ? The codes, 1-2 shift, 3-2
shift and TCC, all at the same time ?

They may not happen all at the same time. Once a code sets, it stays.

Now the question becomes how are they detecting these faults, are there
mechanical state switches in the tranny or is this all coming from an error
comparing the crank to the VSS, which incedentally I wonder exactly how they
deal with that, being a 4WD. I guess they would need a secondary VSS on the
transfer case output for the speedo, or does it just "know" ?

Many ways. The engine knows its RPM. It has the VSS signal. And i
believe there is a signal on the tail shaft for output rotation. It just
does the math. It figures on what gear it commands, figures the ratios,
and goes from there. Probably looks at the internal pressures too.

With these codes now, remembering the symptom:

Reset computer runs fine, afterwhile starts taking off in second and no passing
gear. When it gets hotter it will no longer shift into first even manually.

I wonder if the computer is reading the other two codes because of being in the
limp home mode. Even so, how could it differentiate between anything involved
at times when the TCC should be applied. When the TCC isn't applied how would
it know the stall rate of the torque convertor ? Is their math that good that
they can do it from the MAP or MAF along with the other engine values ? That's
almost scary (lol).

Did you take the trannie electrical plug off and inspect it closely????
Did you measure the resistance of all the solenoids at the trannie plug
and directly on the solenoid?

I say fairly assuredly that the TCC should not be applied in anything but high
gear, wouldn't you agree ? There is one possible fact not known yet,,,,,,,,, is
it POSSIBLE that the TCC is supposed to engage in every gear because they used
a bit of a different design of convertor, like one with nice high stall, but
need the TCC because it'll overheat ?????

On the older cars, this was true. On some of the newer ones i am not so
sure. When TCC slip gets much above 200 rpm difference, its sets the
code. (when it knows the TCC is engaged). If the TCC was grossly
overheated, it will turn color. There is a thin strip of friction
material that the TCC uses for TCC lockup. The TCC will work normal
otherwise.

www.phoenixtrans.com/html/lockuplowdown.pdf


(assuming the rest of the trannie is ok)

This comes up because now I remember that the thing was picked up out of town
and during the trip it pushed out some fluid. It had to have been overfilled
because it wasn't real low when it got home. I wasn't on the trip, but I heard
there was quite a bit. Was it expansion, or maybe the torque convertor started
cavitating ?

Well, if you lost fluid and your level is ok, you definitely were
overfilled. My relatives windstar puked when it got too hot due to VSS
failure. Not a good thing for the trannie.

Bob

 

[BOB URZ]

I looked at my shop manual and here is s a little more information:
There are 5 shift solenoids in the trannie, All are fed from a common 12 volts from the
fuse box, (on my truck fuse 24 10A).
the input wire is "E". From "E" on the plug, 12 volts is fed to all
the other solenoids.
E= 12 volts to these solenoids:
T= TCC clutch
U= TCC modulation
S= 3-2 shift
B= 2-3 shift solenoid
A= 1-2 shift solenoid

All of these solenoids are grounded at the PCM module.
They all normally have 12 volts from the fuse box, and are
grounded at the PCM for solenoid operation.

There are switches in the trannie to confirm to the PCM what gear
its in.
rev/low=N
d3/d2=R
d4/d2=P
pressure control solenoid= D & C

Bob

 

[JURB6006]

Thanks again Bob, I'll be looking into that next. Once I find those test
points, then I gotta deal with the logistics of doing this in a driveway, or on
the street. Maybe I'll pick up some noid lights or something,

I'll keep you "posted"

JURB

P.S. Just so you know I just noticed the email address showing in the posting
window of my AOL newsreader appears to be picking up your correct email. The
(remove) is not there. I just thought I'd let you know, because I am an extreme
spam hater. Even junk snail mail, I use their prepaid SASE to send back, you
guessed it, junk mail, but somebody else's. You should see what I do to
telemarketers, I talk to them for a good ½ hour before finding an excuse to get
off the phone right away, of course without buying anything. Funny they don't
call as much. I wish I could do something like that to spammers.

JURB

 

[JURB6006]

One new question;

Just exactly happens if the power is lost to all solenoids ? Fuse blows, what
it just revs up and sits there, or does it take off in second or third and
disable passing gear, ummm, for example.

Reason I ask is that some other similar vehicles have experienced taking off in
second and the dash went out. This has been found to be the ignition switch in
a couple of cases. Really if the fuse blows it's blown, but a switch.In this
case the vehicle doesn't have the digital dash (IIRC) and being a 4WD it might
just have a seperate VSS for the speedo.Now I'm not trying to shove a symcure
down your throat, but I think test one will be to see if power applies to the
topside of those solenoids.

Believe me, when I get back under the thing I'll check those connections, and
if that proves nothing I'm going to find out what is and is not being driven.

With your advice I'll definitely make sure the electrical end of it is OK
before money droppage.

I will do what you suggested, soon, but if you happen to know, if it were to
lose all power to the solenoids, what would it do ?

I think this is a crucial piece of information here. Can you drive home with
the tranny fuse blown ? This also comes back to the ignition switch if it
applies the voltage TO the tranny fuse.

If the tranny is reporting to the PCM what gear it's in, WHY ? Because it still
has valves, and maybe a pure hydraulic mode to get you home ( ? ? ? ? )

 

[Bob Shuman]

I can't help on the Blazer, but I know Chrysler electronically controlled
transmissions will default to second gear if they encounter a sensor
reporting a problem in what they call "limp home" mode. In most cases, with
the Chrysler transmissions, this is most often caused by one of the speed
sensors failing. If the speedometer still works, then it is usually the
input speed sensor that has failed. If the speedometer no longer reports a
speed, then it is the output sensor. Both sensors are about $25 each at the
dealer and fairly simple to change (5 minute job). On the Chryslers, they
tend to fail often. I've replaced two in different vehicles and each had
about 50-60K miles. Another common failure in Chryslers is the solenoid
pack.

If the Blazer is anything like the Chrysler trans, if it fails and does go
into 2nd gear, do not drive it far or long since it places a great deal more
stress on the internals. Many people I know who started with a simple $25
part that needed to be replaced have ended up requiring rebuilt
transmissions at up to $2500. Again, I'm not sure if this information is
useful or not, but have to believe that the designs are similar and may even
share third party components, such as the electronic speed sensors.

Good luck!

Bob

 

[Asimov]

"Bob Shuman" bravely wrote to "All" (17 Nov 04 08:39:23)
--- on the heady topic of "Re: 97 Blazer 4X4 ECT problem(update)"

BS> From: "Bob Shuman" <[email protected]>
BS> If the Blazer is anything like the Chrysler trans, if it fails and
BS> does go into 2nd gear, do not drive it far or long since it places a
BS> great deal more stress on the internals.

And don't forget to replenish the engine oil as it tends to get by the
rings a lot while doing over 60mph in 2nd gear.

A*s*i*m*o*v

.... A couple of volts below threshold.