2019 L5P First Problem - Chevy and GMC Duramax Diesel Forum
2017+ L5P Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 20 (permalink) Old 07-01-2019, 05:39 PM Thread Starter
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2019 L5P First Problem

My truck and gooseneck trailer loaded weigh in at 25,000 lbs. truck will pull this load as fast as I would want to go, but to slow the fuel burn rate down I set the cruise at 60 hit tow/haul and let her eat. Going into North West Arkansas there are a couple of climbs that 18 wheelers have issues with that drop their speeds from 65-70 mph down to around 35-40. I know that these climbs are out there but in my mind my truck is smart enough to know when to down shift or help itself out, correct? Truck has done fine going the first 20-25 miles up hill with out any real problems speed is at 60 mph, tach setting about 1700 rpm, engine temp according to CTS is 200 degrees trans is about 190 degrees. Going up this long climb about half way up dash lights up and says "A/C turned off", I look at all gagues again, engine at 210 tans at 190 oil pressure is about 30 psi 5th gear 1700 rpm 60 mph, so I think well the truck is thinking for its self lets see what happens now, about 1/2 mile later dash flashes "Reduced Engine Power" and I'm like what the heck, recheck gagues and engine is at 250 and climbing, trans at 200 oil 30 psi still in 5th gear 1700 rpm and 60 mph, about 200 yards to hill top so I just let it eat to the top, as soon as I crest hill engine temps starts to drop, on the down hill run of about 1-11/2 mile temp goes back to about 220 everything else is the same, start up next hill about a 1 mile pull the temp starts to climb to 240 and then I get the "Reduced Engine Power" message, top out at 240 kick cruise off and drive the rest of the way using the foot feed never over 60 going down hill with grade assist on and never over 2200 rpm on any other climb??? Had truck to dealer today to check for codes and they could not find any (which is what I thought would happen) anyone got any ideas???
Sorry this is so long but want to get as many of the details in as I could.

Thanks!!
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post #2 of 20 (permalink) Old 07-01-2019, 06:54 PM
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Rad fan clutch problem?
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post #3 of 20 (permalink) Old 07-02-2019, 07:22 AM
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Originally Posted by redwngr View Post
Rad fan clutch problem?
I agree with this, did you hear the fan engage?

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post #4 of 20 (permalink) Old 07-02-2019, 07:39 AM
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You are pulling way to much weight for your truck. The L5p was a very small exhaust side configuration, small up pipes, small exhaust turbo vanes, etc. So I am guessing the ECM was seeing some very high EGT’s and cut power to keep from melting pistons.
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post #5 of 20 (permalink) Old 07-02-2019, 07:44 AM
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Quote:
Originally Posted by Gatordog View Post
You are pulling way to much weight for your truck. The L5p was a very small exhaust side configuration, small up pipes, small exhaust turbo vanes, etc. So I am guessing the ECM was seeing some very high EGT’s and cut power to keep from melting pistons.
Not that much over maximum GCVWR of 24,500lb, though??
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post #6 of 20 (permalink) Old 07-02-2019, 07:54 AM
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Quote:
Originally Posted by Gatordog View Post
You are pulling way to much weight for your truck. The L5p was a very small exhaust side configuration, small up pipes, small exhaust turbo vanes, etc. So I am guessing the ECM was seeing some very high EGTís and cut power to keep from melting pistons.
I think @M.A.M. would disagree with your statement. The dually L5P has a towing capacity of at least 23k and a GCWR of over 30k (with the same gearing as the SRW, so there's no difference from an engine standpoint), so the powertrain can handle it. The SAE dyno test for these engines requires sustaining maximum rated power for quite a while, so there's no reason it should be overheating under the conditions described by the OP.

I agree with @redwngr that it sounds like a cooling system issue.
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post #7 of 20 (permalink) Old 07-02-2019, 08:42 AM
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Seems to me thereís a cooling issue somewhere. I grossed 26K pretty much daily, and Iíll make a run down to Georgia, through the WV/VA mountains once every month or two. I pull over size, so there is a ton of wind resistance from the front as well, making the engine work quite a bit more. Iíve never seen my coolant temp over 220. I can hold the pedal to the floor going up a hill, and usually right around 214 it starts dropping pretty quickly (thermostats open, rad fan fully engaged).

Seems to me itís either the coolant temp, or possibly EGTís that are triggering the ECM to reduce power. Seems unlikely that it was EGTĎs, Iíve seen 1400+ degrees at the manifold for the duration of a hill, and Iíve never had power reduced.

OP, are you watching this data on a CTS2 monitor, or on the dash?


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post #8 of 20 (permalink) Old 07-02-2019, 06:35 PM
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@Doverarjim any updates today?

Was fan running wide open?

Pretty unmistakable sound I'd expect.


Dirty radiator, or road trash picked up and stuck in front of it?

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post #9 of 20 (permalink) Old 07-03-2019, 03:44 PM Thread Starter
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Sorry guys been working to much!!! Shop looked at it and as usuall could not duplicate problem, no codes were stored. To answer the fan questions no I did not hear the fan kick in and roar like my 11 truck did. What gets me the trans never downshifted, rpm did not go up or down it just toqured it up and over the hill? The grade braking worked it would drop down to 4th to hold at 60 on some of the down hill runs. Also for the second regen it did it while driving in town, stop and go driving never over 45 mph took about 12 miles and .6 hrs for it to complete!!! Not sure if my truck has gremlins or I'm just lucky!!!!! I did not get a chance to talk to the tech that worked on the truck he was working to finish up on another job so he could start vacation so I told him that I'd come back by when he got back and visit with him to see if he has any ideas that might be the cause. Thanks guys!!



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post #10 of 20 (permalink) Old 07-03-2019, 05:43 PM
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I'd say cooling related, as many have said the fan kicking in is unmistakable. I leave Friday for our yearly outing to Colorado, l5p is gonna get a good workout.
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