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 FIXED!! B7, AUX & primary brake & coolant lt. on
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bwest
Administrator

United States
2324 Posts

Posted - 01/31/2013 :  2:54:13 PM  Show Profile  Reply with Quote
So what would cause this? Swapped multi-function alarm module & flow switch with known good unit. Checked and corrected ground problem on brake lights and checked and didn't find any problems with wires going to brake light switch. When we started this endeavor the warning lights would come on almost constantly. After fixing the ground problems on the tail lights we slowed it down but didn't stop it. Now I am going to replace the booster because it is leaking (not much) up where it mounts to the firewall. There is no problem with steering or braking when these lights come on. It has to be an electrical problem I just can't find it!

Edited by - bwest on 02/06/2013 06:46:42 AM

Wolf0r
Top Member

USA
2179 Posts

Posted - 02/01/2013 :  06:52:26 AM  Show Profile  Reply with Quote
Brian I can send you some PDF files on diagnosis of these hydro units. Does it do the 4 second test when you start it up? If the coolant light is on constant with the sensor unplugged the green wire is pinched to ground somewhere, which may cause the MFA screw up. Also note even though they will plug in, the MF modules differ from diesel, gas, air brakes, etc. Careful swapping them out with the wrong one, can lead to madness!

“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson
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bwest
Administrator

United States
2324 Posts

Posted - 02/01/2013 :  11:40:21 AM  Show Profile  Reply with Quote
Thanks Wolf, All my buses of this vintage are diesel so I don't think I have a problem there. I have a second one now that the electric motor is not coming on when you press the brake without the engine on. This is the one I swapped MFAs with. I also put a steering gear on this one and brake pads. As a cartoon that my kids listen to says, What's up with that?

Bryan
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Wolf0r
Top Member

USA
2179 Posts

Posted - 02/05/2013 :  06:36:54 AM  Show Profile  Reply with Quote
Grab what you need. I'll have it up for a while. http://www.mediafire.com/?cinf33fs16h4c

“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson
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bwest
Administrator

United States
2324 Posts

Posted - 02/05/2013 :  09:57:51 AM  Show Profile  Reply with Quote
Well, it's blocked here at school. I'll have to pick it up at home tonight, if I don't forget.
Thanks
Still wrestling with this. On the second bus found out that the flow switch wasn't making contact with the booster housing properly. Guess I know "what's up with that" now don't I? lol
Changed the booster on the first bus because it have been leaking a bit anyway

Bryan
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bwest
Administrator

United States
2324 Posts

Posted - 02/05/2013 :  12:39:27 PM  Show Profile  Reply with Quote
Alright, I've narrowed this thing down. Now every time I accelerate hard the lights come on. Even if I brake torque it sitting still. I think what it's doing is disconnecting something making the MFA module think it's starting up and it's going into a test mode like when you first start it. It just stays on a second or two and then goes off and then if your still accelerating hard it does it all over again. I have been all down underneath this thing and even put a new end on the ground wire connected to the left frame rail right below the P/S reservoir.
Any ideas??

Bryan
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bwest
Administrator

United States
2324 Posts

Posted - 02/05/2013 :  1:47:35 PM  Show Profile  Reply with Quote
Wolf, can't view you documents. I got to the site and saw your files but it says items are not available at this time, try back later. All your files are like this. Thanks anyway

Bryan

Edited by - bwest on 02/05/2013 2:09:17 PM
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bwest
Administrator

United States
2324 Posts

Posted - 02/05/2013 :  2:08:01 PM  Show Profile  Reply with Quote
OK, here's the latest. I laid under the dash in the driver's floor board and with the engine running I pushed the throttle by hand. I could see the throttle base was loose. I tightened the two nuts on the outside firewall but this did not solve anything. I have noticed that if I slowly push the throttle by hand and then stop (and stay in that position) when the lights/ motor comes on it will continue to cycle as if it is doing a test over and over. Any thoughts?

Bryan
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bwest
Administrator

United States
2324 Posts

Posted - 02/06/2013 :  06:53:34 AM  Show Profile  Reply with Quote
OK, here's the fix if anyone else has this nightmare of a problem. I replaced the alternator about 2 1/2 weeks ago. After a few days the tach went out and I told the driver not to worry about it, that I would write it down and fix it later. Well, what he didn't tell me was that on occasion these lights were coming on. They continued to get more often and then he finally told me. Not his fault, he knew I was busy here in the shop and he knew the brakes and such were working fine. Anyway, I pulled the belt from the alternator and started it. No warning lights came on!! Put a new alternator on and the problem is fixed!!

Bryan
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Wolf0r
Top Member

USA
2179 Posts

Posted - 02/06/2013 :  09:19:18 AM  Show Profile  Reply with Quote
quote:
Originally posted by bwest

Anyway, I pulled the belt from the alternator and started it. No warning lights came on!! Put a new alternator on and the problem is fixed!!



I have replaced the alternator for an inop tachometer before. Never for an AUX brake issue. I need to review the schematic. Awesome you got it fixed and back to temporary sanity.

Edit: Looked at schematic there is a yellow wire at A2 on your alarm connector. "Hot when charging" These schematics are PDF weird you can't open them. http://www.mediafire.com/view/?2d5703o0q1e5zme

“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson

Edited by - Wolf0r on 02/06/2013 09:29:10 AM
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bwest
Administrator

United States
2324 Posts

Posted - 02/06/2013 :  10:30:30 AM  Show Profile  Reply with Quote
I really need to thank the guys over at Central States too. You know, my local Chevy dealer was real good on these but they are really out of practice as of late because so many people have gotten ride of this vintage.

Bryan
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Wolf0r
Top Member

USA
2179 Posts

Posted - 08/26/2013 :  09:14:36 AM  Show Profile  Reply with Quote
I had a used 1999 GMCV in here with electrical tape over the aux brake and abs lamps and a inoperative tachometer. All I did to fix this one was put the tach wire on the right terminal. "R" which is next to the battery stud. It was hooked to the "I" stud. Same A2 circuit 53 wire on the module drives the tach and starts the self check. To check the "R" terminal with a DMM it should read half of the alternator output about 7 volts running. Just something else to look for when the AUX BRAKE is staring you in the face.

“The good thing about science is that it's true whether or not you believe in it.”
Neil deGrasse Tyson
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