ISX 870 jake brake issue

[Jose9640]

I have an issue with the jake brakes on this 870. Hit the switch to level 3 and you can hear the jakes come on but very very weak. If I go to level 1 or 2 it feels exactly the same. I hooked up insite to the truck but there was no codes for jake brake. What should I look for? Insite showed 33% on level 1 67% on 2 and 100% on 3

[Chamberpains]

Those percentages show that the ECM is recognizing the 3 different stages you command. Your problem is probably gonna be in the engine (possible solenoid or rocker), jake wiring harness, turbo, or the turbo plumbing and actuator system.

What boost pressure readings are you getting under a full load pulling up a hill? Psi under load stage 3 full jake down hill? Stage 2 down hill? Stage 1 down hill?

Your problem sounds like a solenoid not responding. Has the solenoids or harness to the solenoids ever been looked at? Pop the valve cover and give the harness and connections a healthy look over. If you don't know how, go to https://quickserve.cummins.com/info/index.html and register your engine for free. It will have all the info you'll need to check out your problem. Step by step.

[Rawze]

(07-09-2019 )Jose9640 Wrote:  I have an issue with the jake brakes on this 870. Hit the switch to level 3 and you can hear the jakes come on but very very weak. If I go to level 1 or 2 it feels exactly the same. I hooked up insite to the truck but there was no codes for jake brake. What should I look for? Insite showed 33% on level 1 67% on 2 and 100% on 3

Chamberpains is spot on.

some things that come to mind, listed in no particular order here...

Wiring and solenoids are common culprits. They will not always throw a code for this.

Next would be the mechanics of the jake rockers. things like the their built-in actuators(pistons), etc.

Next would be the oil pressure in the head. If it is weak, then the jake will be weak. Check the overhead cams for excess wear, and check the oil pressure is 34+ for the engine going down the road.

Next would be the wear in the rocker bearings. if there is excess wear in the rocker bearings, or the rocker shaft(s) then it will significantly lower oil pressure to the upper part of the head.


Also can't forget that the ISX uses the turbocharger to increase its effectiveness of the jake brakes by making the turbo produce high amounts of exhaust back-pressure. If there is any issue with boost or manifold leaks or with the turbo positioning/pressures being correct, or if the turbo exhaust impeller is damaged or worn down from carbon packing then it will effect the jake brake directly. It will also usually effect the boost pressures for the engine too by some degree. A proper boost gauge is your best friend in any turbocharged diesel engine.

[Jose9640]

I checked the resistance at the solenoids they ohm at 9.8. Boost pressure when jakes on high doesn’t seem to be above 5psi.

[Chamberpains]

Your within spec's. I pulled that screen grab from Cummins quickserve. Its FREE! Make an account and Register your ESN (engine serial number).

The info to troubleshoot it is under Service; Manuals; Service Manuals; Signature,ISX,QSX15 Services manuals; Section 20 Vehicle Braking Group 20.

After that, follow everything step by step to ensure things are good and possibly find your problem. If you run down everything and still have a problem, come on back, let us know what you did and we'll go from there.

[Chamberpains]

Your boost pressure is the pressure of stage 1 jake. What is your max pulling boost pressure?

From the info you've given so far it looks like possibly only 1 solenoid is working. There is a lot of different problems that can cause this with no codes. Rawze listed most of them.

[Jose9640]

I checked both solenoids. Both are within spec. Normal boost pressure is 30-32 psi.

[Rawze]

(07-09-2019 )Jose9640 Wrote:  I checked both solenoids. Both are within spec. Normal boost pressure is 30-32 psi.

30-32, its in a turbo derate, turbo is going to have a shortened lifespan from the extra heat. Normal for 870 is 36-38 psi.