Confused: Intermittent speedometer with limp mode, NOT output sensor!

Hello!

'93 Intrepid ES 3.3L 66K miles.

I just had the tranny rebuilt due to some other problems which
turned out to be internal (AUUUGGGGHHH$$$$), but I still have a
problem I've had for over six months now. At any speed and any
driving conditions, the speedometer will drop to zero and the tranny
will drop to second. (If it's not in second already.) The output
speed sensor has been replaced and no codes are thrown. (Checked with
a code reader, not the ignition trick.) Tech at the xmission shop has
no idea what might be causing this, other than it's probably in or
after the TCM or PCM.

Does anyone have any info on the signal flow between the speed
sensor, TCM, PCM, speedometer, and where in this chain the decision to
kick in limp mode is? The intermittent nature of the problem leads me
to suspect a bad connection somewhere. Since this one ain't gonna be
solved by slapping a code reader in the system, it's probably going to
be a trace through the wiring type of fix. I figure if I tackle it,
it will cost some time. If someone else tackles it, more $$$$ that I
don't have!

Here are some other intermittent problems that occur, in the hopes
that someone out there might say "Aha! All these circuits have "X" in
common."

The low fuel light will occasionally come on, even though the tank
is nowhere near empty.

The parking brake/brake warning light may come on for a few seconds,
but the parking brake is fully off and the brake system is fine.

The RKE has operated intermittently for the past several years.

Even though the HVAC fan is on the stop below max, sometimes the air
flow out the vents drops considerably. Rotating the temp control a
couple of times brings the flow back to normal.

Thanks for any info!
DSF

 

All these things are hooked up to the BCM (body control module).
On my 97 Sebring the inside fuse panel integrated on the outside
of the BCM. I'd open it up and check the circuit board for any bad solders etc
and clean all connectors.

/Pelle

 

the trans controler is losing power and or ground causing it to go limp in
mode
and i have seen this many a time after the trans was rebuilt only to be
the real cause
of the trans issue
there is a wiring harness that runs under the radator and runs to the
trans controler in that harness is a red wire with a white tracer inspect
that wire from left to the right side meaning pulling it out of the
packing you should also find a splice in it that might be corrioded most
that i have repaired were towards the right side

 

The most probable answer is you are loosing the data bus signals that
pass between different modules. The instrument cluster gets the speed
data from the transmission sensor and the transmission gets the engine
RPM from the engine controller module. You need to have someone use a
data bus analyzer to see what is happening.
One of the modules may be babbling and using most of the bus bandwidth
sending garbage.

 

Thanks for the info. I'll check into the wiring as soon as I can.

I would like to get to the BCM and check the connections, etc. It's
mounted in the dash on the metal plate under the air duct to the
passenger door. I can't figure out any way to get to it short of
removing the entire underside of the dash. I can see it and I can
grab it from under the dash. It has quite a bit of wiggle to it.
(I'ts not tightly mounted.) Is that normal? Does it maybe (fingers
crossed) snap out? I'd really hate to pull the whole lower half of
the dash only to find out there is an easier way to do it!

BTW, I assume it's the BCM i'm looking at. My service manual has it
on the same side of the car, but lower. It has three multi-pin
connectors on one end; one of which is not used.

Thanks,
DSF

 

That is a good idea, but my interior fuses are on the edge of the
dash where it meets the driver side door. (The fuse cover is part of
the cover for the duct that feeds air to the door vent.) My BCM is
in the same place on the passenger side.

Here's part of the response/questions I gave to mic canic. Anyone
know the answers?

I would like to get to the BCM and check the connections, etc. It's
mounted in the dash on the metal plate under the air duct to the
passenger door. I can't figure out any way to get to it short of
removing the entire underside of the dash. I can see it and I can
grab it from under the dash. It has quite a bit of wiggle to it.
(I'ts not tightly mounted.) Is that normal? Does it maybe (fingers
crossed) snap out? I'd really hate to pull the whole lower half of
the dash only to find out there is an easier way to do it!

BTW, I assume it's the BCM i'm looking at. My service manual has it
on the same side of the car, but lower. It has three multi-pin
connectors on one end; one of which is not used.

Thanks,
DSF