BAC Forum
General Boards => Technical Support => Topic started by: Roger Davis on February 18, 2022, 06:51:43 PM
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Hello all. I am new to the forum and just learning how to navigate the site so please bear with me.
I went to exercise my main engine and generator when I realized I could not start the main engine from the key. While attempting to start, I happened
to notice the transmission shift pad indicator light which would normally show an "N" which was there for a moment and then flickered for about 10 seconds
and went out permanently. I am able to turn the key to the run position and start the coach from the remote start/stop buttons in the back bay and can turn the coach off with the key. It will not shift as there appears to be no power to the shift pad. I pulled the key switch down to test for voltage on all positions
corresponding to the key and is working as it should. I have found an old thread on this subject but it appears my situation is slightly different. I might add
I checked the solenoid in the electrical bay and would have jumped it however it appears to be functioning fine. I'm betting it's a relay somewhere so I'm
asking for some guidance. Thanks to all.
2001 Beaver Patriot 40' 3126B 330HP
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Roger,
From your description sounds like you are not getting ignition power to the shift panel. Since you said the panel flickered before losing power I suspect a bad connection. There is a fuse for the panel that I think is buried in the console that the panel is mounted in. It may have a corroded or loose connection. If wiring is same as an 02, power comes into the panel from C43, pin 1. See Coach Assist (BAC Web site) for the wiring diagrams.
Steve
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Roger,
Go ahead and jump the solenoid in the front run compartment. I have seen where they have continuity but won't transfer amperage under a load. Please advise, Fred
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Roger
When all else fails there is a service troubleshooting manual for the Allison automatic which will give you better insight into the system and how to track down your particular problem.
It is in the coach assist library
Eric
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Roger
The first place to look is in the battery compartment you should find two inline fuse holders one is ECM power for the engine
And the other is for the TCM ( transmission control module) direct power these 10 amp fuse holders are usually tied to the bundle of battery cables behind the battery tray and batteries .
It's not uncommon for this fuse holder and fuse to corrode from exposure to battery gasses.
Eric
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Thanks everyone for responding. I'll spend today going through all your suggestions starting with the two fuses in the battery compartment. In my life, it's never
that simple but maybe I'm due a break. I'll post my findings along with any new questions and again, thanks for the help.
Roger
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Roger
Had a similar problem on a similar coach a year or so ago. Fella had spent a ton of money pulling the Allison control module and tracking wiring.
Solution was a new solenoid in the front run bay. Check for good contact on the two small posts. If you have the type with the resistor across the two posts it could be bad but when you do replace this solenoid be sure to get the exact one.
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Okay, after working on all the things you guys and I could think of, I'm no closer to a solution than when I started. Here is what I do know. The solenoid
in the electrical bay is working perfectly. While in the elec. bay I opened the black Allison relay box and checked both fuses and checked for 12 volts on said fuses with ignition on. All good. There are no fuses in the cavity under the shift pad and as I mentioned the black Allison box is down in the electrical bay.
I should also mention while in the electrical bay and with the key on, I checked everything except the relays for 12 volts and all good.
Back in the battery bay I checked everything with a fuse including the relay tray and all fuses were good. In hind sight I probably should have checked for voltage as well. As Steve suggested C43 pin 1, many of the writing on the connectors has rubbed off so I can't identify C43. Maybe you could describe it another way. There are older threads of similar problems but they fixed theirs. However I read something regarding a solenoid similar to the one in the electrical bay that's way behind the batteries and almost impossible to get to. With the key on I checked for voltage but either solenoid is not working or wasn't actuated since I don't know what it goes to. Maybe one of you will know. If C43 is the coupling to the shift pad that is my next thing I will be checking
directly at the pad as it is still dark. I suspect I could HOT wire a lead from the ignition to the pad with a fuse but I think I'll save that for a last resort.
I eagerly await your next suggestions. And once again, thank you all!
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Roger,
The solenoid you are questioning behind the batteries is the "trigger" solenoid that activates the starter solenoid on the starter. It is activated only in the "start" position. It is not what you are looking for. I would look for the main plug coming from the transmission near the frame rail. Look for corrosion inside at the pins. What is the chassis battery voltage at the batteries? what is the voltage at the transmission ECM? Fred
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Fred, just so I'm sure I understand. Where is the plug located on the coach that you want me to address. Please be specific and I will perform all that you
say but this is my first time addressing this system on the RV so I need you to talk me in please.
Roger
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Roger
To get shifter operation you require battery power and ignition power and grounds to the transmission ECM
It's time to check at the ECM for the presence of these .
In the coach assist library document Allison troubleshooting manual on page 761 you will find a wiring diagram for the 3000 and 4000 series ECM.
His should help you identify which pins to check
Hope this helps
Eric
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Eric,
Is this the metal box in the left of driver cavity under the shift pad or somewhere else. If somewhere else, where please?
Also do I test this with key ignition power on or off?
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Yes I believe so a picture would help
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this one?
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Hard to tell from the picture but ya that should be it.
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Roger
On page 106 in the troubleshooting manual gives the pin out for low voltage codes which would apply to you condition.
Dtc po880 on page 290 should be a better discription of your problem and the pin out at the ECM to check for power a d grounds to the ECM without the ECM powered up both ig itio power and battery direct power the shift concel won't power up .
Eric
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Eric,
I looked at page 126 but from what I get from that, the engine needs to be running first which is the problem. Your first order of business was to
remove the harness from the TCM and check for voltage and ground and of course corrosion. I'm going to start that now and will report my findings.
As far as reading codes from the plug, and without a digital reader capability, I have no idea how you want me to proceed. While I am fiddling with
connections, I will also check the shift pad for 12v and ground (which I don't expect to find unless the pad is fried). Also I wanted to ask you if there is
a possibility of one of the six relays in the VIM could be bad. In waiting for your response today I tried a search for a replacement for one of those
Bosch relays and thought to switch out one at a time in hopes that might be it but seems to be a discontinued part #.
Do you think a bad relay is possible?
Anyway, I'm heading out to the coach to perform the voltage tests and will report my findings.
Thank you for sticking with me. Hopefully we'll figure it out.
Roger
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Just an aside. Perhaps too obvious but have you checked to see that the remote start button at the rear is switched back to front start?
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Roger
Sorry I only meant for you to use the pin numbers with ECM unplugged to determine if you have it ition power battery power and grounds where they should be .
My bet is you don't have one of the power feeds.
Keith brings up a good point if the rear run switch is not turned to front start you will have no forward controls.
If the rear run switch is in the front start position and the shift concel is dead try switching the back to rear start and checking the consell.
I believe even from the rear start position the transmission has to verify neutral to allow starter operation
Eric
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Roger
I know this wiring diagram isn't the same year model as yours but it should be close .
In coach assist 1996 patriot wiring diagrams page 18 will show you the wiring for the rear start and ignition power flow to the transmission control module it shows the power feed through a relay in the Transmission VIM module.
Before condemning the relay in the VIM check at the rear engine switch they are a common failure due to the environment they live in .
Eric
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Wow you guys have been busy while I have been busy!
Okay first to address rear start station, there is no front/back switch on my coach. Never seen it never switched it.
Next, there is no power to the shift pad with or without ignition on.
The metal box in the picture I sent appears to be of the ECU. Picture attached. It has 3 32pin cables going to it. Blue, black and grey.
If there is anything to check on this module please advise. I haven't yet located the pin chart but I will. With that being said I still have to
locate the TCM. Anybody know where that might be hiding????? Anyway, when I do find it please confirm--I understand I need to check pins 2 and 70.
I'm guessing pin 2 is the ignition.
Am I thinking this correctly??
Roger
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Eric,
I'm looking at the 1996 wiring diagram page 18 as suggested. CB21 & CB22 would certainly be suspect however they've been tested and are fine.
At the top right hand corner there are 2 20amp fuses directly in a vertical line from each other. Might you know where they are actually located?
Roger
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Roger
Sorry for the delay the two inline fuses are those found in the battery compartment.
Do you have transmission power to the shifter when in the rear start mode at the service panel ?
Sorry just read your post that states you have no rear run switch.
Do you have a picture of your service bay ?
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Good morning Eric,
Thanks for hanging in there with me. Here is the pic I already have in my phone and I assume you are referring to this bay vs. the electrical bay up
front driver side. I still need to know where I might locate the TCM with that 80 pin connector and if you would please confirm which pins to check.
I'm guessing pin 2 and 70 with pin 2 being ignition.
For a mere $12 I am buying a VIM relay and will change them out one at a time just to either rule out or hopefully solve the issue.
As far as your question as to when I start remotely and with the engine running, the shift pad is still dark. Just to add...the picture does not include
the relay tray w/fuses however I have checked all of them and all good. Is any of them the 20 amp ones in the '96 wiring diagram??
Roger
ps if you request more or better pictures of service bay, just ask
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Eric,
I took the following pictures so you might see everything. Please let me know if you'd like to see anything else.
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Roger
Have you checked in the compartment under the shift lad to the ?eft of the driver's seat for the TCM
when. Checking for TCM power and grounds
For battery direct power should be 12 +volt at pins #70 and #10
For ignition power should be 12+ volts with ignition turned on at pin #63
The TCM should be grounded at pins #69 and 6
The low voltage tests mentioned earlier will help you with these pin numbers and location in the 80 pin plug
Just ignore the criteria for setting the code the fault is the same with the exception that the fault did not take place with engine running.
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Eric,
I just got done swapping all 6 relays in the VIM and unfortunately, no joy. The only thing in the cavity under the shift pad left of the driver
was the metal 3 harness ecu for the Allison. I am yet to find the TCM with the 80 pin plug so I can test for 12 volt. I was really hoping
you were going to direct me to it. Is it possible that it's attached to the frame rail somewhere in the back of the coach and only accessible from underneath?
Roger
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Roger
I'm sorry I just went back and checked your pictures the metal box you have found is the Allison TCM how ever your coach has a newer Allison configuration the old 80 pin unit was referred to as ( W tech 2 ) the system you have is called A tech 3 it was the next generation of Allison controls and the trouble shooting manual is different .
We don't have that one in the library yet so we'll have to do some research.
Did you have voltage at both fuses in the VIM module with the key on ?
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Eric,
I'm glad I don't have to crawl around like I was fearing. Something worth mentioning, My coach is a 2001 and that seems to be the year missing
from coach assist wiring drawings. I can see similarities as I've been toggling between different years.
Does anyone know if there is a fuse inside that silver box? Anyway, if I understand you correctly, you're attempting to find drawings for that TCM of mine.
Once again, thanks in advance,
Roger
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Eric,
Sorry forgot to add, yes to voltage across both VIM fuses. One of them always 12volts the other only when key is on.
Roger
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Eric,
I found it here and am reading through it now.
https://www.trucktransdiag.com/downloads/wtec3.pdf
Roger
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Eric,
On page 192 is the gray wire connector chart. I see battery power on pins 1 and 16 with ignition sense on pin 26 but for the life of me where does
it get ground from? The metal box is not used as a chassis ground by way of an external wire or mounting screws. Anyway I'm continuing to read
I'm just wondering if you agree with my pin assessment?
Roger
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Roger
Allison calls it's grounds battery return
They are pin 17 and 32 in that diagram and should be gray wires .
You will find both the powers and grounds are provided through the VIM module.
He's the 1 and 16 are battery power and the 26 is the ignition power
They usually use two power feeds and two grounds too provide enough current capability through the small ECM pins.
Page 67 in the troubleshooting manual will help identify the pin locations in the ECM and the pins for the power inputs to the VIM module.
Page 83 will show you the power path through the ECM over to the shift concel and the pin numbers to check at the concel as well as plug configuration.
Hope this helps
Eric
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Good morning Eric,
First off let me thank you once again for helping me grind out my homework.
Next, let me see if I follow your thinking. I'm going to test the Allison ECU (TCM) gray cable for power and ground and ignition sense with ignition on.
If no joy, go back to the VIM where voltage to the TCM originates.
But, if both fuses have voltage on them in the VIM, isn't that it's own verification that the VIM is supplying voltage forward? But I'm getting ahead
of myself prior to checking the TCM gray cable. Also I might add that the Power Pin to the shift pad is a different pin according to the drawings on
this TCM so it could still be the shift pad. I will check again the shift pad pin "R" for 12v.
Please comment on my "critical path".
Roger
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Yep
Your right on you could start at the shift pad and work backwards if you like
If you have power at the fuses in the VIM then it follows that you should have power to the gray ECM terminals ( unless you have a loose connection or bad wire in that harness.
Also if you have power and ground to the shift concel it should light up at the very least with cats eyes to tell you it has no communication with ECM if power and ground are there and nothing lights up the problem is likely a bad shift concel.
Eric
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Eric,
Thanks for confirming the critical path. Question, on page 200 is the pin "signals" so I'm interpreting power on pin "R" and ground on pin "P".
Assuming this is correct, I am concluding that if there is power and ground on the cable to the shift pad, then the shift pad is bad and the worst
case scenario is a bad TCM if it is receiving proper voltage.
Correct or incorrect???
I might throw in that all my cabling appears pristine as in clean protected and corrosion free so I'll be very surprised indeed of wiring ends up
being the problem. I'm awaiting your confirmation on shift pad voltage before I dive in.
Roger
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Yes
The separate sensor wire is a 5 volt reference wire that the shift concel uses for it's logic circuits to determine shift input status the same 5 volt reference is also used for other sensors like the TPS ( throttle position sensor) and temp sensors ect.
The ECM uses the sensor return voltage as it's sensor data for it's logic.
The shift concel communicates with the ECM via a serial stream data ( twisted pair) meaning the concel receives and sends data back and forth to the ECM the concel has its own processor built in to receive and send command status and receive gear selected data from the transmission through the ECM.
Sorry if this got a bit wordy
Hope it helps you
Eric
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Hi Eric,
It's the shift pad which I would have realized the first time I checked it but I was checking the wrong pins due to following the pins of the WTEC2. No matter, thanks to you and the others I have learned so much more about my coach which is priceless so a big shout out and THANKS to all! It's the less expensive of the two electronic parts that it could have been so I'll be grateful for that. I've seen that parts like this can be purchased as refurbished for considerably less with a warranty and all so the online shopping begins.
Might you have a suggestion for this? At least the hunt for the culprit is finally over. WHEW! I think I'll take the boat out in the ocean and get my head straight! I have another project involving pulling a cat 5 cable for the new Xantrex inverter from the bottom bay to just above the passenger's head as the existing wire isn't compatible. But that's for another day but soon.
When the new part gets in I'll let you know it's working.
Roger
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Roger,
Glad you got a handle on it. Eric is a great chassis technician and knows his stuff! The Cat 5 short cut is thru the refer cabinet. Cheers, Fred
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Roger
The last PM I sent you is actually a link to a company that rebuilds the shift pads and will test it for you just to be sure
A company called TRANSMISSION INSTURMENTS
https://www.transmissioninstruments.com/
https://www.transmissioninstruments.com/wteciii/
Hope this helps
Eric
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Roger, do you know Xantrex makes an adapter so you can use old cable with new inverter? I did this and all works fine.
Freedom SW telephone to network cable adapter 808-9010
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Hello again everyone,
It's been a few weeks since my last post on this topic so I wanted to share the conclusion. First I want to give a huge shout out to everyone for helping out with an extra big shout out to Eric McClean as without Eric's interaction, I might very well be struggling or possibly have given up and thrown money at it. It turns out it was the ECU and not the shift pad. It is imperative that you use a 9v battery and check the shift pad not just the 12v and ground which in my case were present. There is a 5v pin which if it is not included in the shift pad test, it will not light up. Transmissioninstruments.com is a small family business out of Texas that specializes in rebuilding Allison transmission ECU's, shift pads, and a few other electronic components. I might also
add that I was informed by them that the 2001 and surrounding year parts are notorious for power supply board failures. I asked John if his fix addressed this issue and he said none have come back as of yet. Just in case anyone's interested, there's a 2 year warranty on his work. That's pretty amazing for electronic work!!!
Just in case I included the shift pad in the box so they could test it (no charge for this). I was also informed that the shift pad almost never fails if anyone's interested. So, for $595.00 and my cost of shipping to them (they pay shipping back), my coach starts from the key again and of course shifts as it should.
Again, thanks to all of you for your assistance!
Roger Davis