Testing Jake Brake Solenoids

Glennman · May 25, 2025, 03:10:01 PM

I've been working on getting my Jakes working on my 2002 MCI Series 60. They engage when pushing down on the little button on the top of the solenoids, and oil shoots straight up. However, I'm trying to figure out how to test the power. It seems to me that the only time they would have voltage is when they are engaging (which would be difficult to check while driving!). I've taken the bus to a shop and had the system checked while driving on the freeway with the technician. According to him, everything electrically checks out (no codes, they function properly electrically with the brakes, etc.), but they do not activate while going down the road at all.

How do you check voltage, and at what times would they show voltage?

Thanks everyone!

luvrbus · May 25, 2025, 06:22:37 PM

The Jakes on the series 60 are interfaced with the ABS brakes and the B500 on MCI's you can turn the Jakes off and on with engine ECU the rest is done with ABS brakes and the B500,unless the b500 has been programed 4th gear is the last gear they will work.Then will not engage if the engine can see over 2100 rpm,unplugh the Jakes and run a direct wire from the Jakes to the drivers area you can turn off and on and check the power or you can check the power at the rear JB when on idling ,scan the engine ECU and be sure the Jakes are activated if not you will not get any codes, good luck it can be fun

Glennman · May 25, 2025, 10:40:44 PM

Great ideas luvrbus. My B500 kicks down to 4th gear when I hit the brakes and stays until I press down on the throttle. Do I need take the bus for a drive, get it to kick down into 4th gear, and then turn on the Jakes to see if they work then? I can't say I've tried getting them to engage when the transmission is in a "kicked down" mode. I'll give that a try tomorrow. I'll weigh back in and let you know if it worked. Thanks!

Iceni John · May 27, 2025, 11:15:25 AM

I know my bus is much different than yours, but I did something similar to Luvrbus's suggestion. I was afraid that if my Jakes' Bosch cube relay (that's triggered by the DDEC to send power to the solenoids) ever failed, the Jakes would disconnect, not A Good Thing if descending a long hill. I installed a Jake Test switch that sends 12VDC to both solenoids, regardless of anything else: it will activate the solenoids even if the engine's not running. To test the solenoids I first turn on the Jake Test switch, then go back to the engine and slowly turn on the main battery disconnect switch; I can then clearly hear each solenoid clicking on. Easy!

John

Glennman · May 27, 2025, 09:35:01 PM

I have yet to try running the bus to see if the Jakes kick in while the transmission is in 4th gear after applying the brakes. I'll be taking it to the lake this weekend, so I'll try it then.

However, I am not aware of a cube relay for the Jakes that might exist in my bus. I'll have to try the MCI tech line to see if they know anything about that. Do you know if it would show up in a diagnosis? According to the technician I utilized to check and see if the Jakes are turned on in the ECU, there were no open circuits or anything that would otherwise be detected by their test. I am interested in your idea to install a test switch. I'll have to consider that. Thanks!

luvrbus · May 28, 2025, 05:43:49 AM

Quote from: Glennman on May 27, 2025, 09:35:01 PM
I have yet to try running the bus to see if the Jakes kick in while the transmission is in 4th gear after applying the brakes. I'll be taking it to the lake this weekend, so I'll try it then.

However, I am not aware of a cube relay for the Jakes that might exist in my bus. I'll have to try the MCI tech line to see if they know anything about that. Do you know if it would show up in a diagnosis? According to the technician I utilized to check and see if the Jakes are turned on in the ECU, there were no open circuits or anything that would otherwise be detected by their test. I am interested in your idea to install a test switch. I'll have to consider that. Thanks!

There are no relays for Jakes on your bus

Glennman · June 03, 2025, 10:33:29 PM

Just to put this subject to bed for a while, luvrbus is correct that there is no relay for the Jakes. I'll be putting this on hold for a while until I have time to pick it up again. I'll be checking for fuses and things like that, but I have other fish to fry for now, until next winter when travels slow down again. We just returned from the lake (200 miles round trip). We had a great time, but now we're looking forward to the Old Time Fiddler's Contest in 2 weeks. Thanks everyone.