CEL, I/M status, and drive cycles.

I've been trying to clear my recurring check engine light P0405/P1404 for the last nine months. I installed a new NAPA EGR valve last October, and the CEL went away. It came back with a vengeance returning from Georgia after Christmas. I thought I may just have an electrical problem, so I installed a new battery, replaced the positive battery terminal, and re-installed my OEM EGR valve. THE CEL light eventually went away after a trip to Pennsylvania in February, but returned a few weeks later. I started monitoring the codes returned over the next few months. Swapping the OEM and NAPA EGR valves. The OEM gave P1404 consistently with P0405 most times, while the NAPA always gave a P0405 code.

A couple weeks ago I started reading about "drive cycle" because a test of my I/M sensors indicated a "Not Ready" state for the Evap System and HO2 Sensor. I performed the drive cycle steps (warm up at idle, drive a few miles through town with headlights/mirror heaters on [battery load], drive at least 5 miles steady at 55-60 and then coast to a stop, and finally drive a few miles around town***) and ALL systems and sensors returned a "Ready" state. However, shortly after resetting the codes (~30 seconds) the CEL comes back on and the Evap and HO2 sensors report "Not Ready". I've done the same drive cycle in the past two weeks, once with each EGR, and the results are the same.

I believe I may have solved the OEM code P1404 today when I noticed that the pintle was sticking very slightly in the closed position on a small ridge of carbon. Cleaned off the carbon, and sprayed the EGR with carb cleaner. No more P1404 code.

My question to anyone with a scanner that can read the I/M Ready status, is if the Evap and HO2 "Not Ready" status is normal during a non-drive cycle scenario, and if there is a certain number of drive cycles required to PERMANENTLY clear the P0405 code. It's driving me crazy!! :mady:

*** I forgot to mention that the Evap test requires that the tank be between 1/4 and 3/4 full. I will maintain this range unless I go on a road trip.

The readiness monitors reset every time the CEL is cleared, or the battery is disconnected. So if you have done that and are checking the monitors before doing that drive cycle, then yes, that is normal.

The drive cycles for the monitors are meant to be accomplished during normal driving conditions, but some may take a few weeks to set depending on your driving conditions.

I was also having trouble with a 1404 code in Moab this year. When I got back I took my old EGR off, cleaned all the carbon out of it, then also used some de-carbon spray down the EGR tube itself. Let that sit in there for an hour or two, started the vehicle to blow it out and did it again. Haven't had the issue since.

Tomorrow I will do another drive cycle and check the codes and I/M status, but NOT reset the CEL. Then I will check the I/M status again when I get home. If they remain "READY", I will just try doing a few more dedicated drive cycles to see if I can clear this code. In the meantime, I will continue to use my trusty analog "CEL eliminator" (aka piece of construction paper.)

There are some interesting videos on YouTube showing how they can test an EGR valve operation against a set of technical parameters. I don't really want to pay a technician 80/hr if I can clear it by driving. But, if push comes to shove I may have to bite the bullet.

Attempted a Drive Cycle this afternoon, but I suspect that it was too hot (ambient temps over 90, and probably hotter in the garage.) All of the sensors, except Evap, tested "Ready" during initial warm up. The HO2 sensor is usually "Not Ready". The Evap never did pass. I'll have to try again next weekend... in the morning. What a pain!

Sorry you're having troubles Dubl G. Hope you get a handle on it soon.

Have you thought about getting your exhaust checked for too much back pressure? If your cat is clogging, it can throw some really funky codes.

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Originally Posted by tom4bren

Have you thought about getting your exhaust checked for too much back pressure? If your cat is clogging, it can throw some really funky codes.

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I really don't suspect the cat, as my engine doesn't burn oil, my original EGR valve is clean, and the code has cleared on longer trips (which would naturally include multiple drive cycles.) The VX still runs great. I would think that a clogged cat would reduce performance drastically. I've not received any cat related codes, not even O2 sensor codes, since I removed the K&N filter.

If I can't clear the code with a few successful drive cycles I will turn it over to the experts with proper diagnostic tools to determine the cause. Other than this CEL my VX has ZERO faults. :)

I FINALLY got my CEL cleared today. I took it to a Chevy dealer last week, but after wasting my day waiting, they decided they didn't have the software to troubleshoot my problem, so they referred me to another place town, Warrenton Foreign Car.

They determined that both my OEM and new NAPA EGR valves suffered the same failure! Something about a high resistance across one of the circuits (in the M-Ohms versus K-Ohms.) My NAPA EGR was well within the three year warranty, and knowing Warrenton Foreign Car very well (it's right across the street), they exchanged my EGR valve in just a few minutes. Warrenton Foreign car then verified that the resistance of the new EGR matched their shelf unit, installed it, ran a few drive cycles and cleared the code.

All of my A-B comparisons were based on the assumption that the NAPA EGR valve was good, or at least if it wasn't, it would return a different set of symptoms. Because it failed in the same manner as the OEM unit, swapping them out proved nothing. D'OH!!!

I suspect, but cannot confirm, that both EGR valves were somehow damaged by the bad battery and corroded battery cable that I replaced after the NAPA EGR threw a set of codes. I had strange transmission vibrations, my GPS refused to power up, and I had multiple codes when I was returning from my vacation in Georgia last winter. Other than this CEL I haven't had any electrical problems since I had the charging system repaired.

Keep your battery and cables in good condition, or else!

Yes, the annoying P0405 EGR code is back. It first popped up last month when I drove my car into work, in the rain. After work I move my car from one section of the parking garage to another part of the same garage, but closer to the Metro entrance (This is important, trust me.) I only ran it for a couple minutes. When I returned to my car a few hours later, the code came up about 10 seconds after starting the engine.

I cleared the code when I got home about an hour later, and it didn't come back until earlier this week. In the meantime I had driven to the store several times, with no CEL.

But, Monday, I had to move my car from the garage to the driveway, and only ran it for a couple minutes (I told you this was important). A few hours later I moved it back to the garage, and the light came back on. Again I cleared the code. I drove the car to the grocery store Wednesday with no codes. I checked the memory for any stored/pending code. Nothing.

Today, the contractor was back, and I had to move my car again. Same setup. I only ran the car for a couple minutes. I checked for codes after I parked in the driveway, and it was clean. This time it was less than an hour before I moved it back to the garage, and sure enough I got the same P0405 code just a few seconds after starting the engine. It's consistent and repeatable. That's both good and bad.

I called the shop that checked and changed my EGR valve last time, and they agreed to bench test my EGR valve compared against their bench unit. I don't know what I want to see. Another BAD EGR valve? What makes them go bad? Is it from driving in the rain? Bad wire bundle? What if the EGR checks good? Do I then just make a habit of driving MORE than 2 minutes? Just be prepared to reset the code and drive on my way?

It's frustrating! Everything else in the VX operates perfectly, even the windows and CD player! Why does the EGR valve have to be such a pain?

Maybe I'll just buy one of those eBay specials, and run a few continuity checks myself. At least then I'll be able to troubleshoot this myself instead of relying on a shop that changes $100/hour. :mad:

UPDATE 16-MAR-2015 - NAPA replaced the EGR valve back in November 2014 under warranty a second time and I have not had any codes return since. (I know this will jinx me, and it will fail the next time I drive it.)
UPDATE 21-MAR-2015 - AAAARRRGGGHHH!!!! I should have kept my mouth shut. Got a P1404 code today! Hopefully, it was just my driving style that tripped the code. I cleared the code and will keep my fingers crossed.
UPDATE 24-APR-2015 - The P1404 popped up again after a 125 mile highway speed drive from Pennsylvania. I'm worried about this "new" EGR valve.