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 CE 200 Hyd. Brake Lights Come on with Key Off
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bwest
Administrator

United States
2324 Posts

Posted - 02/21/2014 :  11:57:58 AM  Show Profile  Reply with Quote
I have a 2005 CE200 that the brake lights function normally with key on, engine running but as soon as you turn the key off the brake light come on and stay on until the battery is down,. Any ideas?

Mechan1c
Top Member

USA
696 Posts

Posted - 02/21/2014 :  5:42:27 PM  Show Profile  Reply with Quote
Hmmm...What happens key on engine off?
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C.HARDY
Advanced Member

354 Posts

Posted - 02/22/2014 :  7:29:43 PM  Show Profile  Click to see C.HARDY's MSN Messenger address  Reply with Quote
You have some serious gremlins man......

"Hardybusman"
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misterbill
Advanced Member

United States
303 Posts

Posted - 02/23/2014 :  6:38:31 PM  Show Profile  Reply with Quote
I'm not a bus mechanic, but this makes no sense to me at all. Aren't the brake lights activated by a switch on the pedal? How could you have juice going to the lights with an open switch? Even if it was backfeeding the wrong way the switch would keep the circuit open. They aren't like air brakes where the air pressure activates the switch are they? Seriously, I think gremlins may be the correct answer.

High School Friend-"Hey! How are you! Well, I guess you can't be doing too well, you're driving a school bus."
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bwest
Administrator

United States
2324 Posts

Posted - 02/24/2014 :  07:45:25 AM  Show Profile  Reply with Quote
This whole bus is a gremlin. lol Key on, engine off is same as engine running which is brake lights turn off. I do know I can take the brake light relay out and they go off. I can hear the relay clicking so I know the relay isn't stuck closed.

Bryan
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Fastback
Top Member

990 Posts

Posted - 02/24/2014 :  08:07:52 AM  Show Profile  Reply with Quote
Misterbill, I believe on this unit the brake light switch would be on the master cylinder and not the brake pedal.

Just for kicks maybe try a different relay. Wondering if its an issue with a diode..

Why yes, the ORIGinal CHARGER is a Fastback

Edited by - Fastback on 02/24/2014 08:09:44 AM
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bwest
Administrator

United States
2324 Posts

Posted - 02/24/2014 :  09:07:19 AM  Show Profile  Reply with Quote
I had thought of that (and I will try that) but if the relay was bad wouldn't the lights stay on all the time regardless of key position?

Bryan
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Fastback
Top Member

990 Posts

Posted - 02/24/2014 :  09:39:29 AM  Show Profile  Reply with Quote
quote:
Originally posted by bwest

I had thought of that (and I will try that) but if the relay was bad wouldn't the lights stay on all the time regardless of key position?



Don't know, just throwing out an idea and a caution to not rule out the relay based on its audible noise

Why yes, the ORIGinal CHARGER is a Fastback
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second.flood
Advanced Member

USA
366 Posts

Posted - 02/24/2014 :  10:37:09 AM  Show Profile  Reply with Quote
Pull the relay and check each terminal at the pigtail(make note)key/on and key/off. Ground/hot/open
Determine what changes key/off from key/on.
Troubleshoot from that point.
I never get that lucky that the symptom is always there :)
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bwest
Administrator

United States
2324 Posts

Posted - 02/24/2014 :  11:55:42 AM  Show Profile  Reply with Quote
OK, finally got this thing in and the brake lights are not on now. Thanks, second.flood, for the jinks. Took relay apart and it is clean. So if the relay is clicking, while the key is off, it is getting a signal to power up when it shouldn't. So, I am wondering what, in the world, can be the cause for signal. Does the signal from the brake light switch go to the body controller then the body controller send a signal to the brake light relay?

Bryan
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second.flood
Advanced Member

USA
366 Posts

Posted - 02/24/2014 :  12:47:00 PM  Show Profile  Reply with Quote
When the key is in the ignition position 12 volts from battery fuse F3 will be applied to the brake switch (4036) at pin 2. When the brake switch is closed (brake pedal pressed), the 12 volt signal is applied to the hydraulic brake control unit (9511) at pin 10 through the engine/chassis interconnect (9523) pin C.

A 6.8 volt Zener diode, inside the switch body is wired in parallel with the switch contacts. The diode allows current to pass through it when the key is in the ignition position and 12 volts is applied to the switch. The diode prevents current from passing through it when the key is off and 5 volts is applied to the switch. When the key is on and the brake is not applied, the ESC monitors the voltage drop across the diode and resistor in the switch. If there is an open in the brake switch circuits there will be no voltage drop and the ESC will set a fault.

A 150 ohm resistor, inside the switch body, is wired in series with the switch. The ESC senses the voltage drop across this resistor to check for a short to ground in the brake switch circuits between the brake switch and the ESC. If there is a short, 12 volts from the ESC will be pulled to ground and the ESC will set a fault.

When the brake switch is closed, the voltage drop will change and the hydraulic brake control unit will sense that the brake is applied. The hydraulic brake control unit and the ESC communicate over the J1939 data link.

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bwest
Administrator

United States
2324 Posts

Posted - 02/24/2014 :  1:51:41 PM  Show Profile  Reply with Quote
I did run the codes on this one last week. I got a SID 231 FMI2, SID231 FMI9, SID61 FMI13, SID2 FMI11, SID1 FMI8, & a SID2 FMI8. Also, I have active code SID100 FMI5. I guess I'm going to have to quit fighting it and get hooked up to IKNOW. I have just never had this much trouble with the equipment I have been runing for the last 20 years. I know this is because of several factors, so I'm not pointing fingers here.
Thanks for your help!!!

Bryan
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Thomasbus24
Administrator

USA
3345 Posts

Posted - 03/01/2014 :  6:53:42 PM  Show Profile  Reply with Quote
quote:
Originally posted by second.flood

When the key is in the ignition position 12 volts from battery fuse F3 will be applied to the brake switch (4036) at pin 2. When the brake switch is closed (brake pedal pressed), the 12 volt signal is applied to the hydraulic brake control unit (9511) at pin 10 through the engine/chassis interconnect (9523) pin C.

A 6.8 volt Zener diode, inside the switch body is wired in parallel with the switch contacts. The diode allows current to pass through it when the key is in the ignition position and 12 volts is applied to the switch. The diode prevents current from passing through it when the key is off and 5 volts is applied to the switch. When the key is on and the brake is not applied, the ESC monitors the voltage drop across the diode and resistor in the switch. If there is an open in the brake switch circuits there will be no voltage drop and the ESC will set a fault.

A 150 ohm resistor, inside the switch body, is wired in series with the switch. The ESC senses the voltage drop across this resistor to check for a short to ground in the brake switch circuits between the brake switch and the ESC. If there is a short, 12 volts from the ESC will be pulled to ground and the ESC will set a fault.

When the brake switch is closed, the voltage drop will change and the hydraulic brake control unit will sense that the brake is applied. The hydraulic brake control unit and the ESC communicate over the J1939 data link.





Holy Mother of...

This is what is wrong with new buses. There is NO reason to make a freaking brake light circuit that complex. Its only asking for trouble.

**steps down from soapbox**
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bwest
Administrator

United States
2324 Posts

Posted - 03/03/2014 :  07:00:34 AM  Show Profile  Reply with Quote
I wish there was a "like" button!! ROTFLOL!!

Bryan
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Thomas Ford 85-16
Top Member

USA
4169 Posts

Posted - 03/16/2014 :  07:44:43 AM  Show Profile  Visit Thomas Ford 85-16's Homepage  Send Thomas Ford 85-16 an AOL message  Reply with Quote
The complexity of that circuit is likely needed for cruise control. You need to be able to detect that the brake light switch is still there, so that you do not find out when you need the brakes! Otherwise you could be fighting brakes and cruise control in an emergency. A necessary evil of our modern conveniences. Being involved in manufacturing now, I can tell you we do not add complexity because we enjoy it.
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Thomasbus24
Administrator

USA
3345 Posts

Posted - 03/16/2014 :  5:42:46 PM  Show Profile  Reply with Quote
I've got buses dating back to 1999 with cruise that don't need such a mess to tell the ECM that I'm braking. Lord I hate new buses anymore.
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Thomasbus24
Administrator

USA
3345 Posts

Posted - 03/17/2014 :  04:19:56 AM  Show Profile  Reply with Quote
Ok, I see what you were saying now that I reread it. I still say it's way too complex though!
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Fastback
Top Member

990 Posts

Posted - 03/17/2014 :  05:07:50 AM  Show Profile  Reply with Quote
Pre trip lamp check system is one reason for it to go through the computer

Why yes, the ORIGinal CHARGER is a Fastback

Edited by - Fastback on 03/17/2014 05:09:23 AM
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bwest
Administrator

United States
2324 Posts

Posted - 03/17/2014 :  11:58:09 AM  Show Profile  Reply with Quote
I replace the relay on this unit and it did it again the next night. I schooled the driver on how to pull relay. She did this that night and the thing has never malfunctioned again. Go figure!!

Bryan
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Thomasbus24
Administrator

USA
3345 Posts

Posted - 03/17/2014 :  1:15:08 PM  Show Profile  Reply with Quote
Don't worry....it will act up tonight. Get your jumper cables ready for morning,
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bwest
Administrator

United States
2324 Posts

Posted - 03/17/2014 :  2:17:18 PM  Show Profile  Reply with Quote
quote:
Originally posted by Thomasbus24

Don't worry....it will act up tonight. Get your jumper cables ready for morning,


Bryan
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