tom lawrence

That's referring to a diesel engine. You only have a PCM, which is on the
passenger-side firewall. I believe you already checked those connections.

mopar man

I was beginning to reach that conclusion as a result of searching for
references to the ECM on the web.


Several times.

Update:

I gave up trying to remove the dashboard cover. I did remove the
lower driver-side dash trim, the instrument-cluster trim ring, and
removed the instrument cluster. Removed the cluster PC board, no
dammaged components (looked brand new), noticed that a couple of LED's
weren't installed. Optional indicators I guess - one is labelled (on
the PC board) as "water / door" and the other one as "security". No
corresponding markings on the cluster bezel. For the hell of it, I
soldered a couple of LED's in those positions (along with the
necessary resistors). On the cluster display, they would show up
above the "check engine" light.

There is a massive connector under the dash that's clipped to a metal
bracket coming off the firewall. It's a combination of a large and
medium-sized connector. The large one has about 60 contact positions
(about 50 are used). Again, they're dry and no sign of corrosion. I
re-seated both of them. I believe it's the cable that comes from the
engine compartment through a hole in the firewall.

I did all this with the battery being disconnected (for about an hour
or two). After cleaning the various plastic surfaces and mounting the
cluster, I reconnected the battery, and again there's no change. When
switched to the run (ignition) position, the gauges seem to move to
their respective zero positions (battery to 8v, etc) and the odometer
will eventually display "no buS" and the overhead will display CCD. I
can, however, still start the engine (the tach reads zero).

I found the following:

http://www.turbodieselregister.com/forums/showpost.php?p=932388&postcount=46

and thought that perhaps it might be relavent. I do have remote
lock/alarm/power seats and windows.

Specifically these symptoms:

- Engine Will Not Start (if equipped with Vehicle Theft Alarm)
- No Communication With The DRBIII (No Response from CTM)
- Essentially, all CTM controlled devices will not function if
the CTM locks-up.

There are 2 connectors to this CTM box which is mounted under the
dash. But even when it's unplugged, nothing changes.

mopar man

I was beginning to reach that conclusion as a result of searching for
references to the ECM on the web.


Several times.

Update:

I gave up trying to remove the dashboard cover. I did remove the
lower driver-side dash trim, the instrument-cluster trim ring, and
removed the instrument cluster. Removed the cluster PC board, no
dammaged components (looked brand new), noticed that a couple of LED's
weren't installed. Optional indicators I guess - one is labelled (on
the PC board) as "water / door" and the other one as "security". No
corresponding markings on the cluster bezel. For the hell of it, I
soldered a couple of LED's in those positions (along with the
necessary resistors). On the cluster display, they would show up
above the "check engine" light.

There is a massive connector under the dash that's clipped to a metal
bracket coming off the firewall. It's a combination of a large and
medium-sized connector. The large one has about 60 contact positions
(about 50 are used). Again, they're dry and no sign of corrosion. I
re-seated both of them. I believe it's the cable that comes from the
engine compartment through a hole in the firewall.

I did all this with the battery being disconnected (for about an hour
or two). After cleaning the various plastic surfaces and mounting the
cluster, I reconnected the battery, and again there's no change. When
switched to the run (ignition) position, the gauges seem to move to
their respective zero positions (battery to 8v, etc) and the odometer
will eventually display "no buS" and the overhead will display CCD. I
can, however, still start the engine (the tach reads zero).

I found the following:

http://www.turbodieselregister.com/forums/showpost.php?p=932388&postcount=46

and thought that perhaps it might be relavent. I do have remote
lock/alarm/power seats and windows.

Specifically these symptoms:

- Engine Will Not Start (if equipped with Vehicle Theft Alarm)
- No Communication With The DRBIII (No Response from CTM)
- Essentially, all CTM controlled devices will not function if
the CTM locks-up.

There are 2 connectors to this CTM box which is mounted under the
dash. But even when it's unplugged, nothing changes.

joe brophy

On my '99 Durango slt 5.9l 4x4 I would get the "no bus"
message in the trip odometer display when driving in stop
and go traffic on hot days. The culprit was the PCM. It
had developed a heat sensitive failure after about 30k
miles. It would also shut down the vehicle and would not
provide power to the coil until it had cooled off. Until I
replaced the pcm I would carry a five gallon can of water to
pour over it if and when it began to fail. I also did the
front airflow mods on the passenger side front to help
airflow in the pcm mounting area, as well as changing out
the thermostat for a 185 degree unit per mopar performance.
Allpar listed several cooling mods/changes like an improved
fan shroud and swapping the fan with one with more blades
from a viper but mine already had those from the factory.

Not any further failures since the pcm was replaced. A
friend who used to man the Daimler help desk told me the
cause of the pcm failure was hairline cracks caused from the
PC board in the pcm heating up and cooling down hundreds of
times eventually severing a circuit trace that would be fine
until it heated up and expanded causing the trace to open
slightly. The "no bus" error was generated because the pcm
had shut down, ceasing communication with any of the other
controllers in the vehicle, in this case the dash computer.
I would also get error codes in the high 9xx range from the
odometer readout. Hope this helps, good luck, Joe.

nosey

This probably isn't a high priority on your list but the weatherstripping
can be tightened up by squeezing the weatherstrip channel with pliers. Don't
crimp it closed too tight or you won't be able to get it back on.
--
Ken

tbone

Does this make much sense to you Tom? IF he is getting a no buss message,
doesn't that indicate that the cluster is not talking to the computer or
vise-versa. I doubt that he will get anything this way. If he wants the
diag codes, I think that he will need to buy / borrow a code reader and
connect to the ODBII port directly.


occur.

That sounds like a possible bad ground or bad connection between the cluster
and the PCM sending bogus signals to the gauges.

--
If at first you don't succeed, you're not cut out for skydiving

tom lawrence

Yeah - that was already discussed, later that same day, in fact.

mopar man

I get instrument cluster codes (by pressing the odo shaft when turning
the ignition to on), but not PCM codes (by the 3-times off-on with the
ignition key).

The cluster codes (if that's what they're called) were these:

900 920 921 940 950

Initially when this problem first appeared, the engine would turn over
but wouldn't start. Then after an evening just sitting there, the
problem completely went away for about a minute, during which time the
engine did start, the guages worked, and I was able to get the odo to
flash the (PCM?) codes using the 3-times off-on key sequence. Then
the guages died and the problem came back (no buS, CCD) except that
the engine now starts (but the guages still don't work).

I've been out of town for the past 2 days, during which time the truck
has been in the garage (and out of the rain), and the problem is still
there, but as mentioned above at least the engine now starts every
time I try it (meaning that the PCM is working?).

During the brief time the problem went away, the PCM (?) codes I was
getting were:

P0123 (Throttle Position (TP) Sensor Circuit High Voltage)
P1687 (P1687 Driver 5 Line 7)

Alternate descriptions of 1687:

No Cluster BUS Message No J1850 messages received from the
Mechanical Instrument Cluster (MIC) module

No MIC BUS Message No CCD/J1850 messages received from the
Mechanical Instrument Cluster (MIC) module

No messages received from the Mechanical Instrument Cluster
module

The P0123 code I can understand - since I did disconnect the TP
connector to check for 5V at the connector - but I plugged it back in
so I guess the code needs to be cleared?

What exactly is the P1687 code?


Since the cluster is housed in a plastic case that's screwed into a
plastic dashboard, the grounding must be part of the 2 cluster
connectors. Since I removed the cluster and re-installed it, (and the
connections looked great) I doubt there's any connector issue at the
cluster itself.

The Haynes book shows the circuits for the guages, but it doesn't show
ANY circuits for the electronics in the cluster. The guage circuits
don't seem to connect to any of the cluster electronics. If that were
true, then the computer wouldn't have any sort of connection to the
fuel gauge, in which case you wouldn't be able to read the fuel level
through the ODB port (is this the case?).

As I mentioned before, the battery is fine, and when the engine is
running, the voltage at the battery is 13.75.

Could the problem be located in the wiring bundle that enters the
lower portion of the fuse assembly in the engine compartment, or
perhaps some connection inside the fuse assembly?

The battery guage should at least read the battery voltage correctly.
Are the guages run off a separate power supply somewhere?

mopar man

First let me thank maxpower (aka Glenn Measley), miles, FMB, Nosey,
TBone, Tom Lawrence, and Joe Brophy for the wealth of information and
the detailed answers to my technical questions about the Chrysler Data
Bus (tm)(C). My special thanks to Glen for giving me the encouragment
to continue diagnosing this problem in my own driveway.

To recap:

2001 Dodge ram, short cab, 5.2L, 2WD, all options.

Truck ran fine one day, was parked overnight, there was rain that day
and night, then the next morning engine would turn over but not
start. After 2 days and some poking around
(disconnecting/reconnecting various connectors) engine would start and
briefly the guages worked for about a minute, then went dead, but
engine could then be started at will after that.

When ignition is switched to on, odometer displays "no buS" and the
overhead console displays "CCD".

Not having a proper wiring diagram, I focused on the wiring to the
instrument cluster (MIC). There are 2 connectors (10 pins each) and
after identifying all the ground and power pins, there were about 6
pins that were candidates for being "the bus". One of those pins was
showing 40 ohms to ground, which I thought was strange.

I metered each of those 6 to the 3 connectors at the PCM and found
that only 2 of them did indeed go to the PCM. As I suspected from
examining much of the dashboard wiring, those wires are always a
twisted pair - indicative of some sort of differential signaling, and
I suspected they were indeed "the bus". One of those wires was the
one showing 40 ohms to ground, and now I see it's showing 40 ohms to a
third pin at the PCM (on a different connector).

Ok, so what I do next is this: with the 3 connectors at the PCM
already off, I disconnect as much of that cable as possible. That
basically means to disconnect it's opposite end from the main fuse
module beside the battery (it's a big square connector with a
hold-down bolt in the middle). Ok, I'm still reading 40 ohms - so
what's going on? Under the truck, I disconnect a cable going to the
transmission (it's got maybe 10 wires) and discover that one of those
wires is the one making a 40-ohm connection to one of the bus wires
(this is with all connectors still disconnected).

Ok, time to cut the main cable away from the firewall and remove all
the black tape and physically inspect the twisted-pair bus wires. I
do this all the way to the connector at the fuse module, and still get
40 ohms. The last thing is to take apart the square fuse-module
connector. I do this, and as I manipulate the outer cover, the 40-ohm
connection goes away. I manipulate the wires and manage to make the
40-ohm connection come and go.

I look closely at where the bus wires go inside this connector, and
where the mystery wire to the transmission goes, and it turns out
they're right beside each other. But what's really wierd is that
there's no indication that they're touching. No corrosion, no
chafing, no bared insulation. Very strange.

So I re-position the wires and close up and re-tape the connector,
then re-tape the entire main cable back to the PCM connectors, and
re-install all connectors and assemblies in the dash that I took
apart.

Needless to say, the MIC worked fine, and no PCM or MIC codes were
displayed when I tried the various diagnostic code reporting methods.

I'm thinking that this problem had nothing to do with the rain that
happened the night before this problem started, but I still don't know
why the engine wouldn't start during the early phase of this
situation.

I'm glad I did this, and not simply take it to the dealership and
maybe those monkeys wiggle something and the problem goes away only to
come back later. At least now I know where to look if it happens
again.

maxpower

Gee thanks but I didnt encourage you to work on it!!, but im glad you got it
fixed. I still think it is rain related.

Also I wont to say that I am one of those so called " Monkeys at the dealer"
Let me know when you have another problem!!