CM 870 JAKE BRAKES
11-08-2021, (Subject: CM 870 JAKE BRAKES ) 
Post: #1
CM 870 JAKE BRAKES
Just bought and installed a Cummins CM870 engine with CM870 ECM. Having some issues with the jakes brake. Keep getting fault code 2368- engine brake #3 driver output circuit open. Also jake brake is weak as I am not getting 100% or the 3 stages of engine brake. ECM is outputting to the 3 jake solenoids and INSTE shows brakes at 100% but feels very weak. So I checked jake brake harness and found only two wires for jake brake solenoid #1 and #2 nothing for #3. So I Pulled the rocker cover and to my surprise only two engine brake solenoid were seen as in the CM871 set up.
Does the CM870 head set up comes with two engine brake solenoids ? If yes how would I be able to get the full 3 stages of jake brakes if the ECM is outputting to 3 solenoids and i only have 2 solenoids. Is there a way around this? or What's the fix for this?
Thanks in advance for your suggestions and comments..
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11-08-2021, (Subject: CM 870 JAKE BRAKES ) 
Post: #2
RE: CM 870 JAKE BRAKES
-- Your post implies that someone has made a mess of things because they did not know what they were doing.


* it only takes 2 solenoids to get all 3 stages.

Some of the very older CM870's had the 3 solenoid setup but not all of them... hence there are some factory ecm programs that are meant to drive 3 solenoids.

It sounds to me however that in your case, that you have the newer style of head and jake brake setup,... but the wrong program in the engine ECM.

PUT everything according to the engine ser# as per quickserv.com (including the exact program that is needed for that ser# engine) and there will be no more issues.

Also.. is this engine de-mandated? (deleted)?... and also does it still have its origional VGT turbo on it?.. because the VGT turbo itself IS USED AS tHE 3RD STAGE for the JAKE BRAKE!.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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11-14-2021, (Subject: CM 870 JAKE BRAKES ) 
Post: #3
RE: CM 870 JAKE BRAKES
Hi Rawze I'm still trying to figure out what the problem is.
I confirmed it is the later style head jake brake set up for CM870 I have so its two solenoids as you had said.
The PSN, ESN and SSN all match up as the original which came with the original truck.
ESN : 79155395
ECM Serial number 26047914
Calibration software phase 06050302
ECM code AB10351.16
did all the troubleshooting steps as per quickserve for fault code 2368.
Checked the wring from ecm pin 31 and pin 11 to engine brake harness connector pin 1 and pin 5. all is well no open and no short. Checked resistance of both solenoids and both are reading within specs. Checked engine brake harness and no fault as well.
Checked and monitored on insite and verified all 3 levels of engine brake switch input when selected. (33%, 66%, 100%)
also checked and monitored engine brake output for all 3 levels but engine brake solenoid #2 signal which is engine brake output circuit 2 does not become active at any time. So only engine brake output circuit 3 becomes active when engine brake is requested. So according to the prints on quickserve only cylinders 4,5,6 are providing engine brakes all the time and nothing from 1,2,3

The strange thing is that after a few days driving i get an fault code 2368 which is for engine brake solenoid #3 signal. The fault becomes inactive but after a few days of driving the counts went up to 255 times.
i even checked at the solenoid itself and only solenoid #3 gets 12v. Solenoid #2 remains at 0V.
Solenoids #2 would fire up when a test 12 v was given and same for solenoid #3 so the solenoids are both good.

Now what could be the issue why solenoid #2 (cylinder 1,2,3) is not firing up?
The engine is not de-mandated to "my knowledge" and it still have the original VGT turbo on it.

there also two other codes
1. code 2349 active (112 counts) - egr valve control circuit open
2. code 2346 inactive (255 counts) - turbocharger turbine inlet temperature above normal range.
Could any of these faults contribute to weak jake brake issue or what could be the problem?
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11-14-2021, (Subject: CM 870 JAKE BRAKES ) 
Post: #4
RE: CM 870 JAKE BRAKES
High turbo inlet temp sensor problems are typically an indication that the turbo is absorbing way too much heat because it is being over-worked due to some problems. Something is severely wrong in the exhaust, the intake, CAC.. something to cause this.

That or it has a "delete" program in it and its a horrible program.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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11-15-2021, (Subject: CM 870 JAKE BRAKES ) 
Post: #5
RE: CM 870 JAKE BRAKES
Thank you. I will dig deeper and see what i come up with.
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