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Old 08-29-2014, 11:24 PM   #15
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he talked of the 12v hot at all times wire when off is showing 12v but when key on pulls it down to 7 or some thing

i think there is some thing maybe going on there ?
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Old 08-30-2014, 07:00 AM   #16
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Originally Posted by terry735001 View Post
he talked of the 12v hot at all times wire when off is showing 12v but when key on pulls it down to 7 or some thing

i think there is some thing maybe going on there ?
The logic in the message center changes the 12 volt down to 7 volts with the 7 volts going to the guages.

Fred
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Old 08-30-2014, 11:21 AM   #17
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The logic in the message center changes the 12 volt down to 7 volts with the 7 volts going to the guages.

Fred
he was asking about it and i was unsure

i am very unsure on this setup as i am more a GM guy i think you could beast help him

i all so said the same thing you did pulled out pin some where when he was working

at this time he can not find the 5way in the dy to see if it could be there

giving it was all working intell the dash was pulled apart i am sure a plug some where got pulled on and a pin is not in its place and i am sure its going to be out of site and hard to find
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Old 08-30-2014, 12:43 PM   #18
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After reading terry's post above, I went back and read the entire thread again, and noticed that you say the tach works but the other gauges do not work.

The connections to the gauges are interchangable. The same data goes down the three wires to all of the gauges, and encoding in the data stream gets the correct info to the correct gauge.

I would suggest you move the connection for the tach to some other gauge to see if the other gauge begins to work. It could be a defective wiring harness from the message center to the gauges.

Let us know the final resolution. My coach has the same system so what you find could be helpful later if/when mine fails.

Fred
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Old 09-02-2014, 06:38 AM   #19
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Well some new information on the gauges. This weekend we took a short trip—an hour or so to Twin Lakes, South Caroline, a Corp of Engineers park, well maintained and pretty. We’ve been there before.

I knew the tach was working, so I plugged the front air receptacle into the tach, and the tach worked. On the road, I saw that the speedometer was working, so I plugged the rear air into the speedometer and the speedo worked.

I suppose that this means that the wiring is ok. It seems to put this problem to the gauges. Some kind of mystery. Why would the six small, single-function gauges stop working and not the tach and speedo? I did not try to plug the remaining connections into the working gauges, but since these two worked, it seems to follow that the rest of the terminals would be working correctly also.

Now I guess I need to find some smaller gauges to test this out. I called Freightliner, but one air gauge is $250. I’m going to look around for either some used gauges or some third party gauges.

I’d be interested to know your thoughts on this.
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Old 09-02-2014, 07:16 AM   #20
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Used gauges from the same instrument system might work. Any other gauges will not work. The gauges look for the encoding on the data stream and only use the data intended for that gauge (ignoring the data for the other gauges).

I still believe you have a bad wiring harness or bad connector (and I'm leaning toward bad wiring harness).

What we know: The tach originally worked. When the tach wire connector is moved to a non working gauge, the non working gauge then works.

Before I started replacing gauges, I would move that original tach connector to each gauge. I think you will find that each gauge works when connected to the original tach connector. If each gauge does not work correctly using the original tach connector, then I would suspect some problem with the data flow from the Vehicle Data Computer. (To see what data is available from the Vehicle Data Computer, you would need to connect something like the Silverleaf VMSpc or the correct version of a Scangauge to the diagnostic port......and I really do not think this is your problem.)

Look carefully at the wiring diagram in SB 54-12 and you will see that the leads going to each gauge have connectors in series. All of the data for all of the gauges is supposed to get to all of the gauges. All of your data is getting to the original tach connector, but appears to not get to the downstream connectors.

I believe you have a wiring break in one of those three wires somewhere downstream of the original tach connector.

I do not know how the wiring harness from the message center to the gauges is connected to the message center. If it is a wiring connector, I suggest removing the wiring harness and using an ohm meter while moving the wires to see if you can find a break in one or more of the three wires. If you find a break in the wires, it should be repairable unless it involves one of the connectors.

I think the wiring connector at the message center will be one that looks like the connectors illustrated on page 4 of SB 54-12.

If you find how the wiring is connected to the message center, please let us know to help all of us that have the same system. A picture of that connector would be very helpful.

Let us know what you find. I think you're making progress.

Edit: After posting this I had the thought that possibly you could just have minor corrosion on the gauge/connector contacts at the gauges that are not working. You could also try removing and reseating each gauge connector to see if that changes your symptoms. Good luck.

Fred
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Old 09-03-2014, 06:45 AM   #21
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Thanks, Fred. The one thing I did not do was plug the working connectors from the tach and speedo back onto the air gauges. That I'll do next. The SB shows something called a “spider connector”, which I’ve not located. I did untape and look at the junction where all the wires break off to the separate gauges and did not see any connector or splice. It seems that the gauges are connected in a series. I’ll look farther. Thanks for all help and suggestions.
The
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Old 09-07-2014, 06:43 PM   #22
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Well, back to the gauges after some lawn work and a repair on the MH steps. I located the Spider Harness, disconnected the wiring harness at the Spider Harness (this is the place where all of the wires to the gauges splice off) and checked the connections. They all check okay for continuity. I connected a second ground from the Spider Harness—just to assure that a ground was not the issue. Rehooked everything, but still no small gauges—the tach still works when any of the gauge outlets are connected to it. However, I did find that pin number H, circuit 999, on the instrument sockets had only about .3 v dc. The service bulletin says that that pin should have from 3 to 7 v dc. I checked continuity from pin H on the instrument connector to pin 9 on the 15-pin MC connector and it checked alright for continuity. I’ve yet to check data bus J1587 or circuit RS-485 from VDC to MC which I plan to do tomorrow. Does the lack of correct voltage to pin H at the gauge connection seem to be a problem? Even with this reading, the tach and the MC lightswork. I take a connector that works from the tach and plug it into one of the small gauages, for example, the front air pressure, and that gauge does not work. Plug the connector back into the tach and it resets and works. Thanks for looking at this puzzle and any suggestion would be appreciated.
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Old 09-07-2014, 11:07 PM   #23
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Wow...you've really gotten into this troubleshooting. Way to go!

You're further into this than I've been, as my instruments have not failed. I did learn something about the system at Camp Freightliner several years ago.


If you got .3 (3/10) volts on Pin H, that may be your problem. If you got 3 volts, that would be normal as Table 5 page 13 shows normal voltage is 3 to 7 volts.

If you got .3 volts on Pin H, try to figure where that 3 to 7 volts is supposed to come from.

I think it is the message center that changes the 12 volts to the 3 to 7 volts, but I'm not complete sure of this.

Hang in there.

Fred
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Old 09-09-2014, 07:01 AM   #24
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Thanks, Fred, I spent last evening going over the wiring in the dash. I disconnected the terminals from the MC and found one had some corrosion on it—the one that produces the 3-7v dc. I thought that I had discovered the problem, so I cleaned the pin and terminal, reinstalled, started ‘er up, but no change. At this point, I don’t have the gismo that removes the pin from the block, so I had to innovate some kind of cleaning method. However, the VOM still read fractional voltage. I did notice that the voltage varied from about .1 to about .3 volts. Since this is the information line, it may be that this is the information that keeps the speedo and tach working. Again, I connected the tach to one of the gauge sockets, and it worked. Unplugged it and use the same plug in the front air gauge and nothing. Plugged back into the tach, felt it recalibrate and work. I ran out of time to begin checking continuity from the VDC to the MC; I hope to have time to do that this evening. However, since the lights in the MC work as they should, it seems that the info is getting from the VDC to the MC. But I intend to go over the terminal blocks one pin at a time. To say the least, this is frustrating, but somehow the more frustrating the more determination—that may be the thing that gets me into trouble. I plan to call the Freightliner help line this evening; I talked to a person named John who was patient and helpful. I’m going to see if he will be working this evening or if the techs switch shifts. Maybe he’ll have some suggestion.
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Old 09-09-2014, 09:19 AM   #25
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Does pin H on the message center have 3 to 7 volts? (measured with the spider harness removed) Maybe the message center is not delivering the correct voltage and all else is correct?

The Tach and Speedometer might have different logic than the other guages since the tach and speedometer have a much higher range of motion than the remaining guages. If this is true, it might explain why the tach/speedo work and the other guages do not work with the corrupted .3 volts.

It would be very helpful to see what is on the data bus (diagnostic plug near driver seat) but you would need something like a scan gauge for diesel or the silverleaf vmspc system.

Assuming that you can not fix the guages and that the data bus is delivering the correct into, a last ditch workaround would be to install VMSpc and ignore the gauges. I'm like you, however, as I'd want the guages to work also.

Just think of all the money you're saving, as the average tech would be reading SB 54-12 and doing what you're doing.

Fred
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Old 09-09-2014, 10:55 AM   #26
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humm are we using RJ45 wire fro jumping from gauge to gauge .. if so i would try a new wire as they go bad all the time as there a hard core wire and brake inside all the time

if all wiring is good i may be thinking the plug its self may be bad in the bake of the mane gauge on the line out side

all so i am sorry i did keep calling the diagnostic plug near driver seat a OBD2 plug my spelling holds me back alot on trying to give good info
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Old 09-10-2014, 06:26 AM   #27
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Thanks to everyone for the insightful suggestions. Last evening I did the following: Measuring at the 15 point plug for the MC, the data wires from the VDC are measuring, as I recall, from about 1.5 to 2.5v dc. Still not the 3-7v dc called for in the spec sheet. At the spider plug (with the gauge harness removed), the voltage ranges from .3 to .7v dc. In other words, it seems, there is move voltage being delivered to the MC than the MC is putting out. Next I checked for continuity on the three wires running from the VDC to the MC—two data wires and a voltage wire. They checked okay; in fact, there was very little resistance, less than one ohm on all three wires—with the test wire measuring probably seventy feet. I take that to mean that there is no break in the wires and they are conveying the info from the VDC to the MC. I checked the grounds at the VDC and all tested as good. I rechecked the spider harness for continuity and it checked okay, so I reassembled everything and checked once more. As before, the tach worked, but the two smaller gauges, the air gauges, that I tried still did not change. So at this point, I’m stumped. It does not seem that the VDC (a new unit) is putting out the required voltage—the 3-7v dc called for in the specs. I talked to a tech from Freightliner and he had no suggestion as to why the MC was not putting out the 3-7v dc. He did say that the data wires should be sending the 3-7v dc to the MC; then he did suggest that the gauges were faulty. I’m still not sure about that given the strange data voltage reading. This evening I plan to call back and talk to John, who seemed to be very knowledgeable and helpful. With this last round of testing, I’ve about reached the end of my electronic tech skills; it may be about time to call in the cavalry.
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Old 09-10-2014, 07:52 AM   #28
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Dash gauges do not work

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Measuring at the 15 point plug for the MC, the data wires from the VDC are measuring, as I recall, from about 1.5 to 2.5v dc. Still not the 3-7v dc called for in the spec sheet.

Sorry if I am misunderstanding, but if you measure the voltage on a live data wire that is rapidly oscillating between 0vdc and let's say 5vdc, a volt meter set to DC will show the average of what it is seeing (perhaps 2.5vdc). If you looked at it with an oscilloscope, or possibly a Hold Maximum feature on a high quality DVM with very short sample time, you would see the peak voltage of 5vdc.
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