O2 sensor
1 - 20 of 20 Posts
Joined
·
8,838 Posts
It is for the rear set of cylinders and should be between the manifold and the catalytic converter assuming it is the upstream sensor that needs replacement. I’d just get the front of the van up on ramps and slide under with my flash light and my O2 sensor socket and ratchet and the new sensor with me! It should be obvious.
Joined
·
8,838 Posts
No, upstream means BEFORE the catalytic converter and downstream means AFTER it. Bank 1 is the rear set of cylinders Bank 2 is the front set. How do you know it needs replacing?
Joined
·
1,185 Posts
So much basic info to cover! The van has 4 o2 sensors, 2 in each cat. But it is highly unlikely you need one. There are dozens of conditions that cause an o2 sensor code (P0171?) and none of them mean a bad sensor. Lean, rich, vacume leak, injectors, fuel pump, thermostat, alternator...any of those can/will trip that code. Get it to a mechanic who can diagnose it BEFORE you start shotgunning parts.
If you just can't keep your hands off of it, I would suggest swapping both front o2 sensors with both rear ones, and see if the code moves. This would cost nothing and rule out anything and everything related to the sensors. The front cat is easy to get out, the rear cat requires dropping the crossover pipe. But if the engine was just swapped all of that was apart, so you probably wont have much trouble with the bolts. Whole job might take you a couple hours. You might be able to get the sensors out without removing the cats, but it's pretty tight, especially the rear ones.
From personal experience, I know that all 4 sensors are identical, and the cost about $70 each for OEM. Don't even consider putting in the $30 autozone ones, they will fail/ruin your life in short order.
Let us know what happens.
If you just can't keep your hands off of it, I would suggest swapping both front o2 sensors with both rear ones, and see if the code moves. This would cost nothing and rule out anything and everything related to the sensors. The front cat is easy to get out, the rear cat requires dropping the crossover pipe. But if the engine was just swapped all of that was apart, so you probably wont have much trouble with the bolts. Whole job might take you a couple hours. You might be able to get the sensors out without removing the cats, but it's pretty tight, especially the rear ones.
From personal experience, I know that all 4 sensors are identical, and the cost about $70 each for OEM. Don't even consider putting in the $30 autozone ones, they will fail/ruin your life in short order.
Let us know what happens.
It was a shop that diagnosed the o2 sensor. Today I located this sensor. It's right above the cat on the back side. My wrench was too big for the area to get a solid bite on it. I may find a shop to do it at minimal cost. I replaced the fan assembly unit today. Removed & installed new from the bottom.
Joined
·
1,185 Posts
Fan assembly isn't that bad of a job, especially once you've done it once. It looks crazy at first, but if you remove the grill (both the outer and inner parts) and then you remove the crosspiece (the crossmember the surge tank is attached to) then the fans easily come out from the top. Once the fan is out, then other jobs become a piece of cake, namely the alternator, a/c compressor, all the hoses and heater hoses. Indeed, getting the intake manifold off is super easy once the crossmember is off.
Next time I do this, I'd like to make a video and put it on youtube. At first glance, the promaster looks like a PITA to service, but it really isn't.
Next time I do this, I'd like to make a video and put it on youtube. At first glance, the promaster looks like a PITA to service, but it really isn't.
I didn't do all that to do the fan. I took it out the bottom in couple seconds. Once you unhook the 6 connectors that are plugged in then it's just releasing those 2 top brackets and push up a little and then pull it out from the bottom. This O2 bank 1 sensor 1 is a hard one. At the top of the cat so you can only feel to where you need to put the wrench. I can only fit one arm up there all the way but need a shorter wrench. Shop wants $100 to do.
Wonder if the original poster ended up replacing catalytic converters...
I had similar scenario, replaced motor and after 100 miles or so got a P0420.
Anyone ever replace the rear catalytic converter DIY style?
The front is pretty straightforward but the rear Cat two bolts attaching to the manifold are very difficult to access.
I had similar scenario, replaced motor and after 100 miles or so got a P0420.
Anyone ever replace the rear catalytic converter DIY style?
The front is pretty straightforward but the rear Cat two bolts attaching to the manifold are very difficult to access.
Joined
·
1,185 Posts
They arent too bad. The trick is to do it from over the top of the engine with an open ended wrench. Save time? Have a friend put the wrench on the bolt from the bottom, then you put the force on it from the top.
Joined
·
77 Posts
I definitely didn't DIY it but I did have to replace both catalytic converters before hitting 15k miles. I learned there's a 7-year, 70k mile federally mandated warranty on all emissions components, which the dealer forgot to mention until I brought it up.
What caused the cats to go bad after so few miles?
Joined
·
77 Posts
I wish I knew! I asked the tech when they replaced it and just got a shrug.
I bought the van off auction (3 years old with 14k miles, clean title...though you'd never know it by looking). It was owned by an electrician in NYC before me.
I didn't think cats could go bad with a modern engine these days due to ECU/fuel injection ensuring properly air/fuel ratio (too much unburnt gas is hard on a cat) and gas now being unleaded (lead will destroy a cat quickly).
Joined
·
1,185 Posts
Not so. Our vans have 2 o2 sensors per cat. The upstream one lives at the inlet of the cat, and if the sensor goes bad or the wiring to it is bad, it will read wrong and the engine will run rich, destroying the cat pretty quickly. If the engine runs rich for other reasons (bad ignition, leaky fuel injector, low compression) same story.
They downstream sensor reads what’s coming out of the cat, and compared that to the input sensor to determine the health of the cat. The downstream sensors light the light of they go bad, but otherwise affect nothing.
Interesting! I guess that is a vulnerability with the sensor system.
Joined
·
1,185 Posts
The real problem with o2 sensors is misdiagnosis. Vast numbers of situations can cause too much or too little fuel to get burned, which shows up as a P0420 code. The average person reads that, goes to autozone and buys crappy cheap o2 sensors, and replaces them, and still has the code.
Not for nuthin’ but I have 3 vans, thus 12 o2 sensors. The vans have 1.5+ million miles. 11 of the o2 sensors are original equipment.
Not for nuthin’ but I have 3 vans, thus 12 o2 sensors. The vans have 1.5+ million miles. 11 of the o2 sensors are original equipment.
What are some of the other causes then? I have code P0420 and P0430. The shop I take it to tested the catalytic convertor and said there were no issues there. So before I change out the O2 sensors, what else should I be looking for? I have close to 400k miles on my van, and that's the only issue currently.
Joined
·
1,185 Posts
Sorry, missed this.
The way the computer knows the cat performance is by comparing data from that cat’s upstream and downstream data. That’s also how it derives that cat’s temperature. So i could see a truly bad cat setting a 420, bad upstream or downstream sensors, mismatched sensors, bad wiring on one sensor, leak at cat input, or other conditions I’m missing.
A bank imbalance could trip that, where a bank is lean or rich but the computer doesnt know why.
I’d also question how they tested the converter. What did they do - unbolt it and bolt it to another engine? Put their own sensors in it? They did neither, as that’s a multihour chunk of work.
All that said, replacing the sensors isnt a horrible course of action, since they are $60 at Autozone and $30 at Rockauto. I, however, have NEVER been able to extract them from cats with a lot of miles on them. I wouldnt even attempt it with the cats on the van - especially in rear where they are tough to get to. Generally, you heat them cherry red to get them out. But your shop may know some trick I’m unaware of.
The cats can last forever if the engine has never run rich. But at 400k it’s questionable. The cheapest cats are $240 each at Rockauto but as I say they are tough to get out.
I realize all the above is informative but not helpful. I guess the best advice is to rule out as much as you can that would falsely induce a 420, and then go ahead and replace them.
The way the computer knows the cat performance is by comparing data from that cat’s upstream and downstream data. That’s also how it derives that cat’s temperature. So i could see a truly bad cat setting a 420, bad upstream or downstream sensors, mismatched sensors, bad wiring on one sensor, leak at cat input, or other conditions I’m missing.
A bank imbalance could trip that, where a bank is lean or rich but the computer doesnt know why.
I’d also question how they tested the converter. What did they do - unbolt it and bolt it to another engine? Put their own sensors in it? They did neither, as that’s a multihour chunk of work.
All that said, replacing the sensors isnt a horrible course of action, since they are $60 at Autozone and $30 at Rockauto. I, however, have NEVER been able to extract them from cats with a lot of miles on them. I wouldnt even attempt it with the cats on the van - especially in rear where they are tough to get to. Generally, you heat them cherry red to get them out. But your shop may know some trick I’m unaware of.
The cats can last forever if the engine has never run rich. But at 400k it’s questionable. The cheapest cats are $240 each at Rockauto but as I say they are tough to get out.
I realize all the above is informative but not helpful. I guess the best advice is to rule out as much as you can that would falsely induce a 420, and then go ahead and replace them.
1 - 20 of 20 Posts
Join the discussion
Join now to ask and comment!