Ladies and gentlemen, we have codes. Need some advice. (1 Viewer)

[erkelbot]

So, a couple months back I sold my 05 GX to pick up a 95 LC, and after a few month honeymoon I really missed the GX. So after swallowing up my pride and figuring out my angle with my wife, I convinced her it was better for the both of us for me to get a different GX. Score.

I searched a bit and found myself a keeper. 07, 140K, southern truck, non-nav, blah, blah, blah... The only issues were small -- a rain sensor not adhered, and a few codes registering in the computer. The guy I bought it from said he pulled the codes and they were CAT related. He said the dealer wanted $800 or something to fix. I thought, nope, not for me, but let's go ahead and use that as a negotiation tactic and discount the truck assuming responsibility for the fix myself. I drove it, and it drove well. I also suspected this guy wouldn't Google if his life depended on it, so I thought, "heck, it might just be a fuel cap..." So, I pulled the trigger and voila, a new truck!

The standard 4 lights are illuminated... CEL, VSC, TRAC and skid. I pulled the codes and got p1442, p1445, p0420, p0430. So, the SAIS is not working as it should. It's not making any weird noises, but we've got a stuck valve. We've also got some readings around the CAT that say fuel isn't being burned off as it should. So I took some pics to remember the codesm and used the OBDII reader to clear the codes. Codes gone.

After driving 15 or so miles, the lights came back as I suspected they would. This time I got 4 readings of p0420 and p0430, which tells me all 4 O2 sensors are either not functioning, or there's still a emissions/fuel mix issue the sensors are seeing. Interesting enough, the SAIS didn't pop up again...

So that leaves me to where I am. I figured the SAIS thing is probably something I should deal with now anyway, so I ordered the Hewitt bypass. I also figured the MAF could use a good cleaning to help read right for fuel draw BEFORE the upstream O2 sensor was getting a read in the event it's pushing too much fuel. My hypothesis is that the MAF could be so dirty that the system is simply dumping fuel at a higher rate than needed. I've also smelled some gas stink, which would corroborate that thought.

My question to you folks is this: would you approach the situation any different, or am I on the right track? Could a dirty MAF cause excess fuel input and cause the downstream O2 sensors to read bad levels and toss 430 and 420? OR, do you think the sensors are bad? Should I be treating the SAIS, or would you leave it? Is there a downside to tricking the system into not running?

Would love your thoughts. I definitely NOT an expert. But I try to play one on TV.

 

[erkelbot]

One other thing to note… The fuel economy seems to be pretty bad at this point. I’ve been poking around town driving modestly and getting around 13 miles per gallon according to the computer (noting they’re historical liars). While this might be incorrect (bit not THAT incorrect), given the fact that I smell gas and mileage is poor, I’m leaning towards a mass airflow sensor issue.

any other insight is appreciated.

 

[GXO]

Clean the MAF. Do the bypass. Do all the O2 with Denso. Passed that you're looking at cats

 

[erkelbot]

Clean the MAF. Do the bypass. Do all the O2 with Denso. Passed that you're looking at cats

Check and check. So I’m clear though, do the downstream O2 sensors with Denso, or all 4?

 

[GXO]

Never mix. All Denso. Bosch have a funky gradient and will code.

 

[erkelbot]

Never mix. All Denso. Bosch have a funky gradient and will code.

Okay, I’m following. But one question... aren’t stock Denso products? That’s why I was asking...are you suggesting I swap out all 4 or just 2 with Denso?

 

[erkelbot]

MAF is clean as a whistle. I have to think it’s all sensor related. My OBDII doesn’t seem to read what sensor is lazy, aside from back and front. I’ll probably swing by an auto parts store and get their read on which sensors are dying and replace what’s needed instead of all at once (unless someone can convince me otherwise). I was just inspecting the upstream sensor, and they’re pretty difficult to get to without removing that splash guard in the wheel well. And when I was monkeying with that splash guard, it started to disintegrate...literally. I can see this project spiraling out of control if I’m not careful

 

[GXO]

Rad rubber has new guards with all new clips for $50. My point was to follow the above. I replaced all my O2s coilpacks and plugs. So you can go big or just isolate the offending part. If the sensors don't fix it you can have a bad cat.

 

[GXO]

That said...pre cat sensors are usually the Problem if you want to start with those

 

[erkelbot]

Thanks — I appreciate it. Would it be possible to have a bad pre-cat sensor(s) and have that throw codes (420) downstream? I hate to replace things I don't need... I have to think getting bad readings upstream would cause the downstream sensor (or sensors) to show a bad reading from fuel mixtures fluctuating too much -- and with too high a variance?

 

[erkelbot]

One last question for the group… Since everyone is so eager to help here…

If a truck sat for an extended period time without being driven, would that cause any of these issues? The truck was owned by an elderly couple prior to me buying it, and I don’t think it got many miles put on it for sometime. Would that cause some of these exhaust and sensor issues? I’m assuming like most other engines, The longer an engine sets without being run the more it will need to work through some hiccups. Additionally, who knows what type of fuel has been in the system or how long it’s been sitting in there. Would old, or lower octane fuel cause issues like this? Is there a fuel additive I should run through the engine a couple times to help clean things up? I’m always a little leery about adding snake oil to my fuel, but I know some people swear by it.

 

[CarolinaGX]

If it was fuel related it would run like crap and misfire. 420 is driver side and 430 is passenger side, the codes dont isolate pre or post cat. The code simply indicates that there is discrepancy between the 2 readings that is beyond the allowable limits. The pre cat sensors are responsible for fuel mixture, the post is simply responsible for monitoring the efficiency of the cat based on the fuel mixture prescribed by the pre sensor. As Dan suggested, use Denso sensors as they are OEM. If that doesnt fix it, then there is a leak between the head and the cats or the cats are failing. You can fill up with 93 and run the crap out of it to get things good and hot to see if it burns anything off but I haven't heard of using that approach on these vehicles.

 

[erkelbot]

I suppose that’s true. It’s running well aside from the lights coming on every 20 miles or so. the codes didn’t detect any misfires — or even the SAIS again once I cleared those codes.

I’ve got all the Denso Sensors ready to go and the special O2 wrench. I’ll also plan on installing the Hewitt at the same time. I’m hoping that’ll fix the issue and get the lights taken care of. I’m also hoping the fuel economy improves once I get the fuel mixture correct with new sensors upstream.

question: anyone know where I can get a good write-up on how to remove the sensors? I’ve seen the passenger side in a write up where you remove the fender splash shield, but if a write-up existed with all 4 I’d be happy. Either way, I’m suspecting it’s a few hour job mixed with some solid patience and beer.

Thanks again, all.

 

[erkelbot]

Rad rubber has new guards with all new clips for $50. My point was to follow the above. I replaced all my O2s coilpacks and plugs. So you can go big or just isolate the offending part. If the sensors don't fix it you can have a bad cat.

I appreciate it — I ordered a set. The ones on there are falling apart when I touch them.

 

[erkelbot]

@Vlad I just realized this was GXOR Dan. Former FB member here -- turned non-member due to wanting to skip 'the book'. Gotta say, the only draw FB has now is connecting with the group on GXOR. I miss that ornery bunch.

Side note: I called the dealer, and I nearly pooped when they said they wanted ~$1,200 for the sensors pre-tax ($330 front, and $270 back). I chuckled a bit and asked about the estimated labor. They said an hour, maybe 2 if we changed all 4. So, ~$1,500 for sensor replacement. Cringe-inducing. I picked up all 4 sensors for about the cost of a single from Lexus -- all Denso -- on Amazon. That's some good savings... Now I'll just have to put in some wrench time and jack up my neck to bring it all home. Any tips?...

 

[GXO]

Buy the sensor socket

 

[erkelbot]

Bought it. I’m no dummy. Most days...

 

[GXO]

Otherwise it's stupid easy

 

[erkelbot]

Well, I found out that stupid easy isn’t quite easy enough. I was able to remove the downstream O2 sensors fairly easily with a break bar, but the upstream ones were difficult. At least without removing the wheel (which I couldn’t do, since I didn’t have a floor jack and was using ramps). Even with the right tool, that is an incredibly precarious spot to get to. I think I read in another thread that the proper way of getting to the sensors upstream is by going through the splash plate shield in the wheel well? Are there other tricks that people found helpful when doing this?

Silver lining: I was able to install the Hewitt bypass along with the proper block plates. Those go in virtually the same location, so there should be no reason why I can’t install the sensors with the right technique.

Now if you’ll excuse me, I’m going to put some icy hot on my back and neck. Ouch...

 

[erkelbot]

Oh, and by replacing the two downstream O2 sensors, I’ve successfully been able to keep the check engine light and all of the other nanny lights off. After driving 50 miles, I plugged in the OBDII scanner and it showed no. It did, however, show 2 pending — my old friends P0420 and P0430. I’m going to drive a little bit more this morning to see if that continues. I can’t imagine that I got so lucky as to I have replaced both downstream sensors and that resolving the problem.

I am also noticing the mileage has gotten better. I don’t think this is a psychosomatic feeling either… I think I’m averaging more like 16 to 17 in the city (measured over 10-15 miles in a stop and go environment) now. Before I was averaging like 13 1/2.