Transmission limp home mode - 96 T&C

A friend has a 1996 T&C with the 3.8l engine.

On damp or rainy days, the transmission suddenly kicks down into
second, even if the vehicle is going at a high rate of speed - awkward
on the highway. From the technical literature that I've read, it seems
like it's going into the limp home mode.

From the wiring diagram in a similar year tech manual, there are quite
a few sensors and/or connections that can activate the kickdown relay.

We took the van to a local Chrysler dealership and they insisted that
the problem was caused by a bad alternator.
The only thing wrong with that alternator (which I already knew) was
minor bearing wear. I insisted that replacing it wouldn't help the
transmission problem. They insisted that since I was not a "factory
trained tech", I didn't know what I was talking about.

My friend paid to have the alternator replaced and of course it didn't
help. One week later in the rain, the transmission kicked down again
at 65 MPH. On dry days, all is perfect.

I asked the dealer service manager if they had scanned the error codes
and he replied saying "we did was was required".

Needly to say that my friend and are are disgusted with the
dealership.

I've pulled apart and cleaned with electronic contact cleaner all
connectors to the power control module, pulled all relays and fuses,
the PCM, visible sensor connections, etc to no avail.

Anyone have any suggestions?

Doug

 

anytime the trans goes into limp mode a code is set. I think the
dealership saw an opportunity to make some money since I am quite
certain they sold your friend an alternator at a cost far in excess of
a simple rebuilt unit. Naturally if they didn't scan the trans then they
would not be able to tell you the code that was set!

Anyway, I own 2 T&C's a 94 and a 95 and done considerable work
on them. I would strongly recommend you replace the
"turbine sensor" aka input speed sensor. These hall-effect
sensors get intermittent when they get older and will cause this problem.
I actually think that they are the only part in the transmission that will
cause this without an accompanying other symptom, such as a big
grinding noise or some such. For some idiot reason known only
to Chrysler's transmission designers, the software in the trans computer
will immediately slam the trans into limp mode even at a high rate of speed,
if the signal is lost from the input speed sensor for even a fraction of a
second, and if signal reappears from the input speed sensor it will
-keep- the trans in limp mode until you shut off and restart the car.

I would discount the rain issue, frankly. The fact of the matter is that
unless your going at a high speed, it is not easy for your typical
ignorant driver to even be aware that the trans has shifted into 2nd.
I strongly suspect that this trans has been doing this for some time now,
and your friend has somehow made some unconscious assumption that
it is due to water, so now he only notices it happening when it is raining.

Ted

 

I will add to what Ted said to say that there is a second speed sensor -
the output speed sensor that will cause the cause the exact same
symptom, plus on some vehicles, like LH cars, the speedometer reading
will go to zero when it's the output sensor vs. the input sensor - I can
only assume the TC is like that too - same tranny - I assume the output
speed sensor is used to derive the speedometer signal in the TC too - if
that's the case, if the speedometer didn't also act up, the problem
would likely be the input sensor - the one towards the front of the
tranny. The sensors themselves go bad, but also you should try cleaning
the connectors (two wires each) at the two sensors first - on the left
side of the tranny - access from underneath. The sensors are about $20
each and are easy to replace - they take a 1" wrench - socket or open
end might be easier depending on access angle in that vehicle. They're
plastic, so don't torque them - just snug them up - they have o-ring seals.

This kind of problem can also be caused by a bad solenoid valve pack -
that's a little more involved (time + $$) to fix. As Ted said, the
codes might tell you something on that.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

It is, on most of them. Only the very early vans used a mechanical
speedo connection to the trans, like the first 3 years I think. Long before
96. In fact, in 96 I think they also did away with the mechanical
gearselector connection from the gear selector knob - the mechanical
"feel" of the selector on the steering column is a completely fake
farce for humans who grew up with mechanical trans linkages.

- if

I've had the input speed sensor fail 3 times, one
time on one of my vans, the other 2 times on the other van, and none of the
3 times the output sensor failed. Do the input sensor first, and if the
problem doesen't go away, then do the output sensor - unless as Bill
said, you noticed a speedo problem.

As Bill says, the sensor contacts should be checked. Also, the input
sensor is right under the trans cooler input and output fluid ports - it's
rubber
hoses that connect to those ports and if the clamps get loose you get fluid
leaks that go right onto the sensor and dissolve the rubber connector
that houses the wires to the sensor.

Yes, it can - the electrical connector to the valve pack should be taken
apart and cleaned, etc.

Ted

 

Ted,

Thanks for your input but NO, it definitely happens ONLY during
wet/damp/high humidity days.

I've driven the vehicle under multiple conditions on dry days and
operation is perfect.

Another clue is that OCCASIONALLY when the transmission slaps into
limp mode, the window wipers will start operating when their control
switch is in the off position.

I'm thinking ground, connector corrosion and/or an alternative current
path.

Now, could the output of that speed sensor be intermittent on damp
days? Sure it can if there is some corrosion, etc on its wiring.
I don't know how to explain the apparently simultaneous wiper problem
unless there is some common ground point that begins to float.
That doesn't seem to be the case per the tech manual.

Nevertheless, you've given me some additional hints.

What is the physical location of the transmission input and output
speed sensors for a 1996?

Doug

 

Ted,

Thanks for your input but NO, it definitely happens ONLY during
wet/damp/high humidity days.

I've driven the vehicle under multiple conditions on dry days and
operation is perfect.

Another clue is that OCCASIONALLY when the transmission slaps into
limp mode, the window wipers will start operating when their control
switch is in the off position.

I'm thinking ground, connector corrosion and/or an alternative current
path.

Now, could the output of that speed sensor be intermittent on damp
days? Sure it can if there is some corrosion, etc on its wiring.
I don't know how to explain the apparently simultaneous wiper problem
unless there is some common ground point that begins to float.
That doesn't seem to be the case per the tech manual.

Nevertheless, you've given me some additional hints.

What is the physical location of the transmission input and output
speed sensors for a 1996?

Doug

Thanks for info on the sensor locations.

I'll crawl under and pull the connectors to check.
If they are exposed to moisture, it could explain the situation.

As mentioned, operation IS perfect on all dry days.

The transmission was rebuilt less than 10K miles ago and the solenoid
valve pack was replaced.

Doug

 

But you already said:

"...I've pulled apart and cleaned with electronic contact cleaner all
connectors to the power control module, pulled all relays and fuses,
the PCM, visible sensor connections, etc to no avail...."

Either you did this or you didn't. Which is it?

Right under the trans input and output fluid cooling lines in the front.
All years of these trans are the same in that regard and your tech
manual should have the info, unless it's not a real tech manual?

Frankly it sounds to me like you didn't clean anything having to
do with the transmission control system. Maybe you thought you
were doing it but you didn't. The trans computer and the PCM are
completely different computers.

You really need a factory shop manual. EBay has many of these.
Or get a subscription to Alldata it's only about $25 bucks.

I do not know 100% on the 96 but I think it is just like the earlier
vans where the trans computer is mounted on the firewall. Right
under the water seal that is between the back of the hood and the
metal frame right under the winshield. If that seal is missing or loose
then your basically pouring a garden hose of water on top of the
big fat many-contact trans computer connector every time it rains.
If you did not separate and clean out this connector with contact
cleaner followed by WD40 then that should point you to where
the next thing to investigate is. The connector does have a water seal
on it.

 

I did clean EXACTLY what I said I cleaned.
I didn't clean the connections to the input and output speed sensors
on the transmission. A the time I didn't know the location and being
under the car, it wasn't readily visible.

I have the factory tech manual for the 2002 year vans. It's the
Chrysler manual. I missed the page where they do show the speed sensor
locations for the 4 speed transmission. I'm sure that's the same in my
friend's 1996.

I'm more familiar with the 3 -speeds. My 2002 with the 2.4L engine has
the 3 speed. It's one of the last vans built with it.

Thanks again,

Doug

 

The sensors are on the side of the trans right under the fluid in and out
lines that connect to the trans cooler. As the trans is transverse mounted
the sensors are at the side of the trans that is nearest the front of the
vehicle

Ted