Seems common: p0401 and p0404

Was driving home this evening, put truck into 2nd gear going downhill and shortly afterwards (IE I have no idea if gearing down in a hill impacted this) the Check Engine light came on.

Truck came with an edge unit on it, I checked the codes, the only ones that we're troublesome were p0401 and p0404.

My understanding is that those aren't worth worrying about, it's a Canadian truck so I don't think it will go into limp mode.

I cleared the codes, but they had reappeared 5 minutes later when I got home. I live in Vancouver, Canada. We have air care regulations here (for one more year) so I can't just mess with the exhaust system. All sorts of bad news... Failing air care is quite expensive so this time around it's probably worth just bucking up and getting the issue resolved. My understanding is that it's generally a gummed up valve or solenoid. The guy who I had inspect the vehicle before I bought it told me it was likely to be an issue in the future.

Truck is 2004.5 LLY 190k 2500HD

Anyone have any advice for where to start?

P0401 EGR Flow Insufficient
P0404 EGR Open Position Performance

For any EGR motor-control or EGR position trouble codes, a Tech II scan tool can be used to perform a "re-learn" procedure, which must be performed whenever any EGR component or its related position sensor have been replaced. In addition, a re-learn procedure can tell you fairly quickly whether the system is operating correctly, or a re-learn may be able to correct a fault where the system has simply lost its position information. Jim

My understanding is that those tools cost a lot of money. And even getting them on the machine at the local shop is I think $120. I'm going to have a tonneau cover installed Monday morning. Those guys seem to know their way around edge units so I'll probably spring the extra $$ to get them to do a relearn. If the problem re-occurs oh well, at least I'll know whats going on.

I used the Edge CTS cleared the codes again today before I left from work and they were back within 5 minutes. Last nite was however the first and only time I've seen the check engine light on.

Thanks much, will update when I get the relearn done.

Those codes usually occur when the exhaust is altered and indicate that the EGR flow is insufficient. It could be a sticking/failing EGR valve as well. These systems can be tricky to diagnose and expensive to maintain which is why most disable them.

I was just investigating, it looks like someone did put on some aftermarket exhaust kit, the two tailpipes are definitely not stock.

I've got several concerns:
* Is this going to cause me problems with BC air care. We've got one year left and then that program is scrapped (thank god). I'm wondering if air care would know if I had disabled the EGR valve.
* The suggestion on the EGR relearn, can I do that with any scan tool? If so I'll go buy one and try it out. Sounds like a good thing to have. Right now the edge unit is plugged in. I'm going to disconnect that sometime soon.

The check engine light hasn't come on again, so maybe the EGR codes are unrelated.

Any suggestions for which scan tools to purchase? Ideally I'd like to have something that interfaces with my laptop or phone. I know some scan tools do that, but I don't know what you can / can't do with them.

I'm going to spend some time researching my options for air care, may be worth bringing to a good mechanic to take a look, at least they'd know what AirCare is looking for.

The scanner you need to do what you think you need to do is a Tech II, or compatible (such as Snap-On). Only a few thousand dollars, on sale (US or CA dollars). Used are a little less, but it must have the 2004.5+ GM Diesel update.

The Edge unit you are using may be a contributor to the problem. Although you may not see black smoke, the particulate matter in the exhaust (soot) is increased on any power setting used. This can, and almost always does, foul the EGR. The EGR can be cleaned, and often is all that's needed.

The aftermarket exhaust system may also be a factor. The reason we install them, is to improve exhaust restriction. This also reduces exhaust back pressure, which also decreases EGR function (the code). If you have or had an EGR code, and the SES lamp was on, it's a sure bet they are related. Very few DTC's are not related to emission system faults.

If the DTC's and SES lamp are only now showing up, it's probably related to a fouled EGR. If it's caused by weak back pressure (aftermarket exhaust system), you would have seen it long ago. "Exercising" the EGR won't likely help on your early LLY engine, in my experience.

To get you through your inspection, stop using the Edge module, get the EGR inspected and/or cleaned, or repaired, as necessary. Allow enough time to be sure the exhaust system isn't an issue. If it is, locate and install an original system (borrow one). Clearing the EGR can sometimes be accomplished by a period of heavy loading (heavy towing), which increases exhaust temperature, and can often help clean it up. Also, if the aftermarket system doesn't have a catalytic converter, it's an instant fail. If it does, you'll only need a "cat-back" system if it comes to that.

Thanks for all the info, I guess I'll be going to a mechanic. No way I'm dropping that kind of $$ on a scan tool. Wife would flat out execute me.

I think it's been throwing the code for a long time, I'm going to disconnect the edge unit and leave it disconnected for the time being. I may pull the EGR valve off and try to clean it before bringing it in for service. Once we're clear of AirCare I'll look into disabling it. I'm only getting 14mpg driving right now, maby the edge is making that artificially worse.

Thanks again.

Gary

I don't see any relearn process or dealer diagnostics doing anything but costing money and wasting time. I see a lot of this where vehicle goes to dealer, dealer does a bunch of diagnostics, disassembles and cleans the EGR all the while ignoring the fact that the exhaust is non stock. Sometimes the issue is cleared (for 3-4 days) and then comes back. OK now we replace the EGR valve itself $$$ Again a brief period of no DTC then problem comes right back.

As for the EGR system causing pass/fail of your testing, my guess is it will fail because of the DTC being present more than anything.

Ok, so mechanic shop down the street from me. Dropped in to say talk to the guy and describe the issue:

* Ok, so having the code showing will definitely fail me.
* He has almost exactly the same truck (dmax 2006 I think).
* He seems to know his way around the EGR issues.

Going to drop the truck off Monday morning and get him to take a look around and see what he can see regarding the EGR problems. He said he doesn't think the exhaust will cause problems with aircare but will be able to get a better look when it's up on the hoist. He's just going to confirm that there is still a cat in it.

In terms of the aftermarket exhaust fouling the EGR I'm not sure what to do there. If I can take the EGR system out of the equation and prevent the ECM from throwing the EGR codes than I'm good to go. Aircare basically just plugs into the OBD and checks the codes.

Anyways, got a really good vibe. The fact that he drives the same truck makes me more confident in him. Family shop, him and his son.

Letcha know what I find out.

It's great that you found a mechanic who's familiar, but your 2004.5 is not the same as a 2006, early or late. His is an LBZ, with an LBZ emission system.

Yah, that's true (LLY vs. LBZ) I had the choice between the 2 when I bought the LLY... For $8k less though.

More importantly though I didn't have to bring it to the stealership... I only have to get through one year of air care apparently and then I'm good to go.

G

@kennedy, question for you.

If I were to get a custom tune from you, that would / would not completely remove the EGR codes? (And presumably help with mileage)?

Also, I realize that driving style is much of the mileage question, when my father had the truck he got better mileage (not hugely, but I've seen the average in the DIC go up when I'm driving by a little and down when he's driving it). If I got a custom tune, presumably i'd want to take the edge module out of the equation, but would I be able to leave edge module connected to the OBD port and use it as a 'gauge' component?

Given I arleady have the unit I'd like to use it if possible.

Quote:

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Originally Posted by gary_lucas

Ok, so mechanic shop down the street from me. Dropped in to say talk to the guy and describe the issue:

* Ok, so having the code showing will definitely fail me.
* He has almost exactly the same truck (dmax 2006 I think).
* He seems to know his way around the EGR issues.

Going to drop the truck off Monday morning and get him to take a look around and see what he can see regarding the EGR problems. He said he doesn't think the exhaust will cause problems with aircare but will be able to get a better look when it's up on the hoist. He's just going to confirm that there is still a cat in it.

In terms of the aftermarket exhaust fouling the EGR I'm not sure what to do there. If I can take the EGR system out of the equation and prevent the ECM from throwing the EGR codes than I'm good to go. Aircare basically just plugs into the OBD and checks the codes.

Anyways, got a really good vibe. The fact that he drives the same truck makes me more confident in him. Family shop, him and his son.

Letcha know what I find out.

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No need to put it up on hoist to verify that cat is in place and you can't diagnose EGR from below. I'd be curious to see if he does a quick look over and sends you on your way N/C or if he gets an hour or more of shop labor.