C12 jake brakes not working check engine light

Hi, I’m new to this site. I have read a ton of useful information on here already. I recently purchased my first dump truck which is a 1999 sterling at9500 with a c12 and Eaton 10 speed. The Jake brakes aren’t working and I would like to address this ASAP. I’m getting a service engine light and wasn’t sure if this could be causing my problem. The truck has the sterling message center and according to it I’m getting several faults which include
SID 22 FM 13 code 3 128
Sid 3 low
Sid 4 bad change rate
Sid 4 sensor amps low
Sid 1 sensor amps low.
I have checked the relays for the Jake brake and they are good. I also pulled the dash apart To get to the back of the switch. The harness coming off of switch has 4 wires, two of which are ground wires. I never got any power out of the other two. I tried with key off and key on engine not running.

 

Also the cruise doesn’t work. So I was thinking there may be a problem with the clutch switch and this is causing both systems not to work. Any way to test this or bypass it to check? Another thing is, truck will automatically start to high idle after it sets for about a minute, only way to get this to stop is rev the motor up and it’ll return to idle for around a minute.

 

You are correct, likely the switch. just jump it with a paper clip to verify that's your issue, you will want to do this on the switch that is at the top of the clutch, they sometime have two switches.

 

Would this explain the automatic high idle??

 

is the trucks coolant up to temp while this concern is happening?

 

Yes I drove it home 200 miles and it would still do it

 

I jumped both clutch switches with no luck. What else can I check? I know that I’m getting 12v to the engine brake switch and that the switch is working. I’m also not getting any power to the engine brake relay.

 

Nobody?? Is there maybe a way to wire the jakes manually where I have to turn them on and off

 

check the wiring harness connection at the back of the head. this is where it gets power to the jake solenoids. make sure youre getting power here, and if you do and not to the solenoids possible wire issue or connection issue

 

its usually on the driver side rear heading down the side if I remember correctly