Performance Exhaust system '05 DMax "Check Engine" Light

Heads up new '05 Duramax owners.
I recently installed a Magnaflow "Cat back' system on my '05 Chevy Duramax. Truck ran great (approx. 40 miles) until the check engine light came on and the rig switched to what I'll refer to as 'limp mode'. Dealership mechanics said the computer read a 'low exhaust back pressure" code and reset the system.
Approx. 70 miles later, the check engine light came on again, same indication. We removed the Magnaflow cat back system, re-installed a stock exhaust system and have not had any problems since.
I've been told by Magnaflow that the application of a performance chip may (emphasis on that 'may') correct the problem. The new '05 rigs have a very sensitive sensor system. Advise hold off on any exhaust system modifications until further research is done.

BTW - Karl at "All About Diesels" has been very helpful regarding the research on this issue. Magnaflow has recognized the problem and is working on a fix.

I am running the predator tuner on mine, and installed a 4 inch system (cat-less), and have not had a problem. I have'nt tried it without the programmer though. The only thing i have noticed is that this thing is a gutless, diesel sucking pig compared to my 04 LB7. Anyone else feel the same?

MPH, my stock '05 takes off like a raped ape. I tried the Magnaflow hoping to improve on the 17.5 mpg I was getting and to help with the slight lag off the line. Think I'll keep it stock for now. . .

At this time only have 5k miles on the odometer

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Originally posted by MPH:
I am running the predator tuner on mine, and installed a 4 inch system (cat-less), and have not had a problem. I have'nt tried it without the programmer though. The only thing i have noticed is that this thing is a gutless, diesel sucking pig compared to my 04 LB7. Anyone else feel the same?

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yup, but with a edge attitude.

i installed my 4" banks that i took off my 01 (cat back)

iv'e set a few codes, but they eventually cleared buy them selves

Interesting. I am having the Magnaflow XL cat back installed Monday 2-21-05 on my ext cab LLY. I have an AFE stage 2 intake and a Predator. My Predator with just the intake on makes the engine very noisy (like marbles in the cylinders) at the 65hp tune. Backed it off to 40hp tune and noise is almost gone. I run Prem. diesel fuel and an additive and still get the noise. I was hoping the exhaust would help, but now I see it might complicate things. I e-mailed Predator and they never got back to me. I asked John Kennedy and he said the programmer probably won't hurt my truck because the timing advance is not that extreme. I think these aftermarket parts companies need to hunker down and do some hardcore testing on their products before they release them. The funny thing is, I was real worried about junking the Allison because of getting too much hp from mods, but the motor will be junk before anything if I can't get some good aftermarket parts.

Hope you have good luck on the Magnaflow installation. I understand the '05 incorporates a new electronic controlled EGR valve system. The dealership advised this may be why the 'low exhaust back pressure' code was thrown.
Good to hear your's is operating okay with the AFE Stage 2 intake system, I'm leary regarding the MAP sensor with mine. Wonder if my California model Duramax is any different from all else. Planning on keeping stock configuration for a while.

Well knock on wood, but my 05 has a 4 inch exhaust with no cc and a pretty straight through muffler and hasn't given me any problems. The turbo is really loud, but sounds kind of weird at idle. I'm not sure if it might be the frequency or what, but it sounds like a jet at the tailpipe. The exhuast is the only thing I have done to it so far.

Codes vs SES illumination will vary depending on the emissions group. The Fed trucks seem to be fine, but will set codes w/o SES light. CA, and Norheast will typically illuminate SES light...

I got the exhaust on, cat back (Magnaflow 304 stainless all welded). Sounds nice, no turbo whistle (I wanted some). Very close to stock sound with a little rumble to it. Truck skips right along with the 85hp tune installed. Still have the rattle noise from the programmer. E-mailed Predator 5 days ago, got a response last night saying "Call our tech support line." I get some cab noise at cruise speeds around 45-55, cruise above and below that speed and it sounds almost stock, except the engine noise from the predator. No SES light. I'll check for codes with Pred this weekend after my gauge install.(Lookout..100HP Tune!!) The 85hp tune makes a power brake very easy and it will smoke the tires through third gear. Pretty neat stuff!

This weekend, I just experienced the same problem. I have an '01 with a Banks exhaust and the Predator. I was hauling a trailer over the Grapevine and the truck went into limp mode consistently unless I babied it up the hill. I've climbed this mountain countless times with the Predator (in 40HP tow mode) and the trailer. This was the first time with the Banks exhaust. The code was "turbo boost exceeded." Must be a backpressure issue since the exhaust is the only new item.

I haven't tried going back to the stock tune yet but will. Funny thing is, I love the Predator tow mode for hauling the Grapevine and other hills and this is where I can't use it with this problem. I'll put a call into Banks and see what they say.


Phil B.

my brother has a 05.he put a silverline dual kit on it.afe stage 2.had predator now has edge.no lights no problems.this system is turbo back.no cat.go figure.

I installed an MBRP Turbo back system on my 05 dually last weekend. Have driven 400+ miles and have no light on and checked yesterday and no codes. I'm also running an AFE stage 2 filter. Put them on at the same time. When I installed the muffler, I reversed the direction of mounting from that shown on the instructions. I put it on with the cups inside facing forward. The dealer that sold the system said this would provide the needed back pressure that the LLY wants to see. I have a Federal emissions truck.

Kennedy, thank you for that info - I was afraid of that, Fed vs. CA emission standards might be what's biting us. Wonder if the thrown codes could be blocked by an aftermarket chip re-programming.
Also wondering if re-setting the codes, then disconnecting the batteries for a while, then reconnecting power will allow the system to adapt any new changes.