Chevy Van: P0446, Evap Vent System Performance

This is a quick easy case study on one I had this week. Common fault code for a less common problem.
I could see some one with the parts changer mentality ending up in the weeds, so I think it's worth sharing even if it's nothing glamorous.

2011 Chevy Express van.
P0446: EVAP vent system performance. Well this is a slam dunk! 10 of 10 need a vent valve. Well, this one is number 11 so keep reading.

Hooked up the scan tool and opened the bidirectional vent valve test. I was rewarded with an audible "clunk" - "click".
On and off no problem. Intermittent sticking is common so we're not out of the woods yet.
Rapid actuation of the vent valve didn't effect it's operation, so I'm done mashing buttons and decide to look at some of the data provided on screen during the test.

Thumbs up to Chevy (no, seriously) for including in the data PIDs "EVAP failure state-excessive vacuum"

A look at the tank pressure shows -6 in h2o. The vent is venting according to data so there should be no vacuum in the tank. I pop off the gas cap thinking the vent could be clogged trapping vacuum in the tank, but pressure remained the same.

Now I'm suspecting a skewed tank pressure sensor. Visual inspection showed the tank had been out, so I bring my finding to the manager.
It is my hypothesis that the fuel pump has been changed with an aftermarket unit which comes with the sensor, and that the sensor is of poor quality
He confirmed that the pump was changed in house back in August.
New AC Delco pressure sensor installed and the van is a fix.

So keep an eye out for those crap ass Chinesium sensors when you're doing Chevy fuel pump modules. Take a couple of seconds and pop that good Delco one out of the old pump and save yourself a come back.

Just for the record, that's 5 cars in 4 weeks that I've seen with faults caused by after market parts.

10 Wrangler with a p0300 from a Bosch o2

08 Wrangler with EGR performance codes from an after market EGR valve (Mopar was $100 more!)

98 Cherokee no start from an after market crank position sensor

2007 Saleen Extreme supercharged Mustang (heavily modified) with a p0306 from a Bosch o2. The whole bank was out of wack, but it only threw a p0306.

I totally get what you're saying and agree. Sort of... This is a very complex topic once you start digging into it. I'm probably not going to do it justice writing off the cuff, but here goes.

Your post reminded me of something a little humbling I learned about 8 years ago when I started working for whom I do now. Without ever giving it a thought, I had somehow come to assume that the OEs made all the parts on the vehicles they sell. That was kind of dumb and I knew better

There are few "OE" parts. OEs source suppliers, who are essentially all part of the "aftermarket". Some parts are so sophisticated that only one source exists. An example would be high pressure diesel injectors, pumps, NOx sensors, etc.

Other parts are more easily duplicated and can, in many cases, be better than "OE".

I will never ever forget a power antenna I was rebuilding way back in the 80s at a GM dealer. I went through 6 magnets that were not magnets and two park switches before I got parts that worked. Then one day you could get a complete antenna assembly for less than the rebuilding parts. The parts supplier changed.

Parts suppliers sign contracts with OEs to produce X number of parts for X number of years, for X price. Many times, you pay more money at the dealer because of this. Pricing calculations for the most part are not all that different between dealers and your local parts store.

Cheaper, better parts often are made by another supplier down the road. So why are we hesitant to buy them? Because the "dealer" part typically is known to be of a specific quality and we want that at the minimum. But the supplier may be outbid down the road or not want to make those parts anymore. So... the "OE" part is now not what it once was. Could be better, could be worse. I've seen both

I probably made a mess of this, but I absolutely understand where you're coming from. I was dragged kicking and screaming to buying non "OE" parts. Recently I needed a blower motor and resistor assembly for my 2006 Envoy. The "aftermarket" parts have been demonstrated to be superior to the "OE". Heck... with this old of a vehicle if I had bought the parts at the dealer they probably wouldn't have been the same parts available years earlier anyway.

Or... and this is the case sometimes... The dealer would have sold me the same part in a different box. That "official" part would have been purchased in bulk from the OE at a different price and distributed to the dealers.

Hey Jim, thanks for taking the time to read my post.

I know exactly what you're saying! There have been instances when ordering parts from the dealer that they bought them from the parts store, marked them up and sold them to me, lol.

Somebody has to make the parts, and it's unrealistic to assume that the OE will continue to produce parts, or contact the same vendor, for vehicles decades after the car rolled off the line.

I will say that in the instances I posted about, with the exception of the Bosch o2 sensors, there was an obvious difference in build quality and materials favoring the factory parts.
That pressure sensor looked like it came out of gumball machine, and the EGR valve was similarly inferior looking looking when compared to the Mopar one.
Thank you for your input, it is much appreciated.

Good info here. I can only recall one time that I know of where I was burned by an aftermarket parts, a MAF on a Vibe. I personally was never able to afford OE parts on my junkers, so never bought them. For personal customers I shop around a bit, always use known good suppliers, and give them the option if there is a large price difference in parts with the preface of possible quality concern.

At the dealer we usually use OE or an approved OE (Value Advantage is ours) unless there is a budget issue with the customer.

We do see the same OE parts failures, in some cases repeat short lived parts. One that comes to mind is with P0456 small leak, nearly every case is a clicking, but still leaking vent valve. There is a bulletin for many Nissans to just replace the o-ring on the valve, but you can usually find at least a whisp of smoke coming from the valve itself. Makes me wonder if a different brand would fix this and they just have a contract with this supplier that needs to end.

This type of failure is gold for our parts changers who will fix it most of the time, but as Noah pointed out, not always. I found two filler neck leaks that had come back from others and sometimes it's the seal around the fuel pump.

Cooling fans on Pathfinders are super common and blower motors on Frontiers. VDO parts in Nissan box.

I'm also skeptical of getting counterfeit parts from suppliers like you might on ebay. Especially trying to get a known brand like Bosch.

Nissan Technician