1991 Grand Villa Check Trans Light is on

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1991 Grand Villa Check Trans Light is on

March 07, 2021, 11:23:51 pm

I went to the storage to fix my door lock, it went pretty well. Following @Chuck & Jeannie write up, I am able to fix the broken door handle with easy. The weather is nice and the coach has been in storage for a few months now. I decide to drive it around to give it some exercise and prepare for the spring break trip.

The old 6V92 engine starts right up without any hesitation. Great!
I was in very good mood.

Then I realize the check trans light is on. I can NOT shift the gear. The gear selection pad is not responsive at all. This is NOT good!

As far as I know Allison transmission is very reliable. But if it went wrong, it is going to be expensive to fix it. I searched one post by @Chuck & Jeannie he spend $709 to reprogrammed the ECU.

Mine is older model without any LCD display. I think it is HT634 series. Engine is 6V92.

Searched this forum, I think I would start from something simple. Hope it is just some connectivity issue.

I measured the voltage on the Trans fuse under the dashboard, on left it reads 14.1V, right is 14.1V. so I think the fuse is good. I did found the fuse above the trans fuse is blown. It is labeled as Vacuum fuse. Not sure what that is. I replace with a new one. But the trans light is still on.

Next I am going to find the Trans ECU and see if there is any loose wire.

Thanks in advance for any of your suggestions and comments

Re: 1991 Grand Villa Check Trans Light is on

Reply #1 – March 08, 2021, 12:02:33 am

Not familiar with your transmission, or your engine, so just some guesses here.

Looks like your idle speed is 850 rpm. Is that normal, or a little high? The later Allison (3060) will not shift into gear if idle speed is high.
Your voltmeter looks OK (although I would expect 14+ volts right after startup), so low voltage probably not a factor.
How about air pressure? Looks like it is reading about 70 psi. At what pressure does your compressor cut out?
Can you shift into drive with parking brake set, or does it need to be released before selecting D or R?

That's about all I got off the top of my head. LIke you said, check any connection plugs for tightness on the control pad and ECU.

Re: 1991 Grand Villa Check Trans Light is on

Reply #2 – March 08, 2021, 12:32:59 am

Chuck,

All 2 cycle Detroits fitted to Foretravels are electronic DDEC II ECU and as such, the idle speed is exactly 600 rpm. The idle speed shown in the photo is elevated by a foot on the pedal. If it really is a 1991, the transmission should be a MTB648 as the engine was derated because Allison did not have a transmission that would handle the torque the 350 hp produced so was dropped to 300 hp until the HT746 transmission was introduced with the 102" coach in '92.

The voltage is about right for right after startup and at that RPM.

Our transmission light does not come on at any time.

In using the ProLink 9000 to bring our idle up to 1000 rpm, the user manual warns several times not to engage any gear as the brakes will not come close to keeping the coach from leaping forward.

And no, the cruise control cannot be used to raise the idle on the 6V-92TA as fitted to the U300.

Suggestion would be to first put a heat source directed at the shift pad. Warm but not hot. Leave it on for a couple of hours. Failing that, pull the connections and check for corrosion and then replug it.

Pierce

Re: 1991 Grand Villa Check Trans Light is on

Reply #3 – March 08, 2021, 09:24:06 am

Quote from: Pierce & Gaylie Stewart – March 08, 2021, 12:32:59 am

Chuck,

All 2 cycle Detroits fitted to Foretravels are electronic DDEC II ECU and as such, the idle speed is exactly 600 rpm. The idle speed shown in the photo is elevated by a foot on the pedal. If it really is a 1991, the transmission should be a MTB648 as the engine was derated because Allison did not have a transmission that would handle the torque the 350 hp produced so was dropped to 300 hp until the HT746 transmission was introduced with the 102" coach in '92.

The voltage is about right for right after startup and at that RPM.

Our transmission light does not come on at any time.

In using the ProLink 9000 to bring our idle up to 1000 rpm, the user manual warns several times not to engage any gear as the brakes will not come close to keeping the coach from leaping forward.

And no, the cruise control cannot be used to raise the idle on the 6V-92TA as fitted to the U300.

Suggestion would be to first put a heat source directed at the shift pad. Warm but not hot. Leave it on for a couple of hours. Failing that, pull the connections and check for corrosion and then replug it.

Pierce

Correct, the engine is 6V92 with rear radiator. so I think the transmission is MTB648.
Yes, when I took the picture yesterday my foot was on the pedal. Trying to build the air pressure faster.
The D2 governor was replaced under @stump suggestion with a 105PSI cut off. Old one is 95PSI. But I am not sure if it is related to the transmission. Air pressure build up just fine.

Searched on the forum, transmission issues seems to be pretty rare.

Re: 1991 Grand Villa Check Trans Light is on

Reply #4 – March 08, 2021, 10:32:20 am

Quote from: Running Odometer – March 08, 2021, 09:24:06 am

Correct, the engine is 6V92 with rear radiator. so I think the transmission is MTB648.
Yes, when I took the picture yesterday my foot was on the pedal. Trying to build the air pressure faster.
The D2 governor was replaced under @stump suggestion with a 105PSI cut off. Old one is 95PSI. But I am not sure if it is related to the transmission. Air pressure build up just fine.
Searched on the forum, transmission issues seems to be pretty rare.

Certainly not an expert on the shift pad as we have not had an issue but I've read others living in a higher humidity environment, have had connection issues in the pad connectors.

I set my D2 to 130 psi as it airs the tires without much of a wait and the cold brakes work a little better on our long 27 percent grade driveway. I have to go down in neutral as first gear overpowers the brakes.

Pierce

Re: 1991 Grand Villa Check Trans Light is on

Reply #5 – March 08, 2021, 10:34:52 am

One thing to check is an oil pressure switch on the engine. It tells the ATEC transmission computer that the engine is running. I had this this switch go out on me. When my switch failed it stayed closed and made the engine hour meter (located next to the dipstick) keep running (24/7). The switch is on the passengers side of the engine, right above the starter. It's plumbed into engine oil galley with 1/8" pipe threads. The sending unit for the oil pressure dash gauge is plumbed with the switch using a TEE: the sending unit is larger and is cylinder shaped.
The switch is generic (added by Foretravel) and should have a cut-in pressure well below the minimum oil pressure of engine (seen when the engine is hot and idling). I think the one I bought was like 2 psi. "Hour meter pressure switch" is the key phase to use.

The oil pressure switch that MIGHT be causing your problem looks like the attached and has two terminals:
- one terminal has a single wire and is has 12 volts all the time (even with ignition off)
- 2nd terminal has two wires, one to the ATEC and the other to the hour meter.

So a quick check of the function of this switch is to verify the hour meter is not running with the engine off and that it is running with the engine on.
When I turn the ignition on my coach the shift pad lights up, I get the "do not shift" indicator ON for a few seconds and then it goes out. I don't know if you are seeing the same thing.

Re: 1991 Grand Villa Check Trans Light is on

Reply #6 – March 09, 2021, 10:49:24 pm

Today, spend few hours try to get rid of the "Do Not Shift" light

Some model information
Engine: Detroit Diesel 6V92
Transmission: Allison MTB648
Shift Selector Allison 23048154
Transmission Control Box: 29504088

I did some research about this issue, most of them point to loose wire connection. I know for sure that the transmission was working fine before put in storage. The major event I guess is the big Texas Freeze few weeks ago.

The Symptom is both Check Trans Light and Do Not Shift light are on. The gear can not be shifted. Coach can not be moved. Engine runs just fine.

To start with the easy part, I bought some electronic contact cleaner. Hope by just clean up the connection will solve the issue.

First start with the key pad. Connection looks good

Then check the transmission control box under the front hood. Connection looks good

Checked the ground wire of the transmission box, use sand paper to clean up the ground contact area. Make sure ground is secure

Go under the coach engine compartment, take off the connector to the transmission, seems good

After clean up all the connectors above, I was hoping the issue is gone. But it is not!

still can't shift into gear

Re: 1991 Grand Villa Check Trans Light is on

Reply #7 – March 09, 2021, 11:07:32 pm

Then I follow what @Pierce & Gaylie Stewart mentioned in his post, I used a hot air gun to heat the transmission control box until it is little hot to touch. The issue is still there.

Then I read the manual, try to read the code. According to manual, turn the test switch one, the check engine light will flash to indicate the code stored in memories.

There are two switches near the fuse. One labeled ENC, then other is Transmission. I am unable to get any light blinking when transmission switch is pushed. Only when the ENC switch is pushed, the CEL is blinking. The code was 46

According to DDECII diagnostic code, 46 means Low Battery Voltage. But the battery voltage is good. It is strong enough to start the engine without any problem

According to MTB 648 ATEC code, 46 means A Solenoid Range Shift. Doesn't know what it means yet.

I was hope to fix the coach before spring break. It seems like very challenging now. I have tried the easiest methods and the problem still exists.

I plan to try the following next

Open the Transmission control box, try to see if there is anything to clean inside the box. It will void the warranty. But I doubt if there is any warranty left for a 24 year old part.

I read some where that the following procedure can reset code

Quote

Turn the key on, do not start the engine.

Move the shift selector to N-D-N-D-N-R-N, pausing briefly (less than 3 seconds) between each selector movement.

Keep search for loose connections.

Drop the pan, change the Transmission fluid and filter.

Really hope I can get the transmission fixed before spring break so that I can take the kids camping. Any help would be greatly appreciated.

Reading post from other places.

In four-speed models, solenoid A is not used. MTB 648 is 4 speed model. So Solenoid A should not be used. Hmm?

The ECU's main power and ground inputs
should be "dedicated" - no other electrical components should share the ECU's power and ground inputs. Yet from the picture, clearly the ECU is sharing ground with other electrical components

Wire 201 is the ECU electromagnetic shielding ground. Ground this wire to the vehicle chassis to
minimize operational problems (improper shifting, false diagnostic codes, etc.) caused by electromagnetic
interference (EMI).
• Ground wire 201 directly to a metal, non-painted portion of the chassis.
• Do not change the wire length.
• Do not connect wire 201 to battery ground or any other ground wires

To clear codes without the ProLink:
1. Turn the vehicle off.
2. Place the Electronic Control diagnostic test switch in the on position.
3. Restart the vehicle.
4. Make sure the park brake and service brake are applied, then shift from neutral to reverse, then
back to neutral.

Code 46
Opens or shorts in chassis harness wires 115 and 121.

Re: 1991 Grand Villa Check Trans Light is on

Reply #8 – March 09, 2021, 11:27:28 pm

Looks like you are doing a good job so far. Have you unplugged and checked the selector connections? Might take a voltmeter and check voltages under the dash using the ignition solenoid voltage as the starting point. Check voltage on both sides of the solenoid when you turn the key on. Storage can increase corrosion and resistance possibly dropping voltage to the point the transmission box voltage is too low.

Do you have the schematic for the 12V electrical system? If not, it's in the media part of the right side above the solid bar at the top. It can be tough to read as it's one of the most complex schematics so it's good to take it to a print shop and have it blown up to as big as they can, then roll it up and store in a mailing tube. Here is the address with both the 12V for the coach as well as the ATEC schematic: https://www.foreforums.com/index.php?action=media;sa=album;in=194

Betting it's electrical rather than an internal transmission problem.

Keep posting as you investigate.

Pierce

Re: 1991 Grand Villa Check Trans Light is on

Reply #9 – March 09, 2021, 11:32:13 pm

In case anyone is thinking of recommending the OP contact Transmission Instruments for help/advice...don't bother. John Kopalek's shop only works on WTECII and WTECIII ECU's and shifter modules.

Transmission Instruments

The MTB648 is a earlier Allison ATEC model.

http://manuals.chudov.com/M939-Series-Trucks/Allison-MT-654CR-Transmission/Allison-AT-MT-HT-Transmission-Electronic-Controls-Operators-Manual.pdf

Re: 1991 Grand Villa Check Trans Light is on

Reply #10 – March 11, 2021, 03:23:11 pm

It is not good. Called few transmission shop around, no body can service this transmission.

According to one shop, MTB 648 is a very rare transmission. The cost of fixing it could easily be over 10 thousands.

I might have to think the start of the end of this foretravel ownership.

Not sure if any scrap yard can take it. Really hate to see it goes to scrap yard. Still have good bones

Re: 1991 Grand Villa Check Trans Light is on

Reply #11 – March 11, 2021, 03:50:41 pm

"According to one shop, MTB 648 is a very rare transmission. The cost of fixing it could easily be over 10 thousands". What a bunch of $%*&. I expect there are a lot of Allison shops that can service the transmission if the problem is internal. I know you are discouraged but it's not doom and gloom. Lots of 648 transmissions on the road. You are just going to have to be more resourceful. First, you need someone to troubleshoot it and find out what exactly is wrong. I never take no for an answer.

Pierce

Re: 1991 Grand Villa Check Trans Light is on

Reply #12 – March 11, 2021, 04:01:17 pm

Shop service and tips manual: Allison MTB647 MTB648 MTB654 Transmission Shop Service Mechanic Tips Manual...

Re: 1991 Grand Villa Check Trans Light is on

Reply #13 – March 11, 2021, 04:30:29 pm

It's not always what the first guy says, example I had the trans filter and fluid changed in a commercial shop on the west coast. They were ready to send me up by Santa Clara to have a rebuilt trans put in at $5,000 plus, I fixed the problem myself, I found out from the forum and confirmed from other sources, it was drive gear for the tachometer. IMHO

Re: 1991 Grand Villa Check Trans Light is on

Reply #14 – March 11, 2021, 04:36:17 pm

Are you sure your not getting any codes from the ATEC flasher? I would suspect some code would be triggered with the check trans light on.

6 years ago I had a problem with hesitation shifting from from neutral to drive. I got the check trans light on and alarm beeping. The ATEC flash code was 32 (direction signals). I didn't get the do not shift light. Called the Allison repair shop in Mobile ALLISON TRANSMISSION HOME | Mysite and the manager (Ken Williamson) told me it was okay to drive from Gulfport.

They dropped the pan, found some sludge and metal, cleaned the valve body, and replaced the forward/reverse switches. Changed the transmission oil, pan gasket, checked the pressure and no problems since. Repairs were $385 as opposed to $6500 for a rebuild which they will tell you if they find metal! Sounds like you may have a similar problem with a solenoid or a switch. You may have to pay for a tow, but any reputable big truck Allison shop should be able to fix it without a rebuild.

Jerry

Re: 1991 Grand Villa Check Trans Light is on

Reply #15 – March 11, 2021, 04:52:04 pm

Thank you guys so much. I can only find some encouragement here.

I have called multiple places today. All of them are negative. Maybe I should try call more places tomorrow.

I call transmission instrument. They referred to jultech. Jultech is probably the last shop still service atec transmission ecu. Jultech is nice enough to send me factory troubleshooting guide. 322 pages. Hopefully it can leads to a fix.

The check trans light doesn't blink at all. Jultech says that might be a sign of faulty ecu.

Wish I had one of the pro link with Allison atec cartridge.

Again thanks for you guys!

Re: 1991 Grand Villa Check Trans Light is on

Reply #16 – March 11, 2021, 05:17:31 pm

Quote from: Running Odometer – March 11, 2021, 03:23:11 pm

MTB 648 is a very rare transmission.

What is rare is that trans. dying just setting.
It most likely is something simple like a mouse eating a wire than it is a bad trans. This may take some looking or searching but it ain't terminal. Was there a lighting strike near by? If so then it may have just killed the ECM.

Mike

Re: 1991 Grand Villa Check Trans Light is on

Reply #17 – March 16, 2021, 12:02:10 am

Another bad day!

Bought a new old stock Allision ECU for this transmission.

Replace the old one, install the new one. Still same issue.

Called few shops, they all refuse to work on transmission this "old".

I don't know what to do next. Anybody know a good transmission shop in Houston area?

Searched online almost everywhere, most of the time. when transmission issue happens, there is no update from the original post. I guess they just give up the rig and move on.

Re: 1991 Grand Villa Check Trans Light is on

Reply #18 – March 16, 2021, 12:11:04 am

Might call Allison's Technical Assistance Center and see if they can provide a repair facility. 1.800.252.5283

Re: 1991 Grand Villa Check Trans Light is on

Reply #19 – March 16, 2021, 01:49:36 pm

To help Mr. Odometer track this one possible lead (we have been messaging) here are some photos of the engine oil pressure switch that sends a signal to the ATEC computer to let it know the engine is running. Apparently the engine hour meter (which is powered by this same switch) is not working so this might be the problem.

Note: the switch in this photo is not OEM. It failed and I replaced with a different style (just due to availability).
If I recall, the OEM switch looks like the one in Reply #5

Re: 1991 Grand Villa Check Trans Light is on

Reply #20 – March 16, 2021, 02:49:09 pm

I had the same issue with my 92 GV however mine would still shift, my pressure switch was leaking went to NAPA with the old one and fixed the problem, trans light never came on again. Not sure if that was the problem but it worked👍

Re: 1991 Grand Villa Check Trans Light is on

Reply #21 – March 16, 2021, 05:09:27 pm

Running Odometer,

You could also try a jumper wire on that oil pressure switch to see if that's the problem.

When I was having trouble with the ATEC relays upfront chattering James T. at FOT told me to do this. With the engine cold It did stop the chattering and the check trans light. I was able to clear the codes except for code 32 (direction signals). When the engine warmed up the chatter would start again.

The jumper does keep the Hobbs meter running with the engine off because you are in effect closing the circuit. You can disconnect it if you leave the jumper on.

If you try this make sure you disconnect the start batteries first or you'll blow a fuse under the dash.

Jerry

Re: 1991 Grand Villa Check Trans Light is on

Reply #22 – March 23, 2021, 12:59:01 am

Some update on my transmission. It is fixed!

It is indeed an electrical connection issue.

I have tried to fix this issue by myself for few days but couldn't make any progress.
I have called multiple shops near by. None of them is willing to service transmission this old. I almost lost hope. Keep thinking about the possibility of worst scenario. Lost quite a few nights of sleep.

But I won't give up so easily, I keep calling around in Houston area. Finally find one shop that is willing to perform a field service

Expert Transmission
Mr. Large
Expert Transmission Inc.
(281) 910 5451

Family run business, three generation transmission shop. Specialized in Allison transmission.
If you call that number, you are probably going to speak with his Mom

.
And one of his daughter is named Allison.

Mr. Large tried to connect to the ECU with pro-link but it is unable to establish a connection. Then he measured the voltage on the J1A connector, the voltage supplied to the ECU is not high enough to turn on the ECU. So at this moment he is already sure it is an electrical connection issue.

After clean up the battery terminal and the connection on the side of the battery compartment. The check trans light is off, the DoNotShift light is off too. Pro-Link is able to connect to the ECU and there is no error code stored.

We take the coach out for a 20 minutes run. Mr. Large is monitoring the transmission using the pro-link while driving. everything looks great. The retarder works great too. I am able to stop the coach much easier.

I am glad the transmission issue is over. I never thought it is the connection issue since the engine starts right up. So I assume the battery connection is good. I guess, that is not the case. The terminal has to be really clean and tight. Lesson learned.

I would highly recommend Mr. Large if you have an old Allison transmission that no other shop is willing to work on.

Re: 1991 Grand Villa Check Trans Light is on

Reply #23 – March 23, 2021, 08:27:38 am

Congrats on a successful resolution! Once again, perseverance pays off.

Re: 1991 Grand Villa Check Trans Light is on

Reply #24 – March 23, 2021, 09:09:04 am

Louis Large is an Allison Guru for sure. He has fixed several of my clients transmissions without them having to go to a shop and at a resonable cost. He is mobile and will range out pretty far from the Houston area. So if you have a concern, call them.

Had a Foretravel that could not get his tranny light fixed in Nac come down to Baytown. Louis showed up and in 10 minutes had it diagnosed and fixed in less than an hour. Knows his stuff.

Fixed my Newell friend's output shaft seal leak in less than two hours. We parked it on the pit I have accesss to in Crosby where Louis could stand up and get that one done. No drips, no spills, no errors.

If I can help you contact Louis or assist with the pit, let me know.

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