# Replacing Front Catalytic Converter



## kupothechocobo (Jan 6, 2013)

On my 2000 Altima (2.5 GXE) I spent a few hours trying to access the upstream catalytic converter. Has anyone replaced the front catalytic converter here? I had a hell of a time getting at the exhaust manifold cover. It looked like I needed to take off the alternator or the radiator to get that exhaust manifold cover off. And then, is it possible to take the upstream catalytic converter off without unbolting the exhaust manifold from the car?

I was able to get the flex pipe off (3 bolts) from the bottom of the front cat without any problems.


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## altimanum1 (Jun 19, 2009)

I have removed the catalytic converter several times on altimas when replacing the engines. I belief you dohave to remove the alternator to remove the left side nuts holding the catalytic and also to remove like 2 small 10mm bolts holding the cat cover.

As far as removing the radiator you dont really have to unless you worry bout hitting it when removing the catalytic. But you do have to remove the radiator fans. Just unplug the two connectors, take the two 10mm screws holding them to the radiator and make sure the lower hose is unhooked from the fans.

Hope this helps.


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## kupothechocobo (Jan 6, 2013)

Great, thanks for the reply. Did you have to remove the exhaust manifold with the front cat, or could you remove the front cat without taking off the exhaust manifold?


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## kupothechocobo (Jan 6, 2013)

Here's a summary of trying to replace the front and rear catalytic converters in a 2000 Nissan Altima with the 2.5L engine. Note: I took some pictures, link is at the bottom of this message. Hopefully it will help if my text is unclear.

In order to access the front cat, first we unhooked the upstream O2 sensor and removed it with the special O2 removal tool by Nissan (it was around ten bucks for a large socket with a slit in the side for a wire). Without the tool, we wouldn't have been able to get the O2 sensor out without cutting the wires (which isn't a problem if you're replacing the O2 sensor). It was necessary to unplug and take the radiator fans out (two electrical connectors and I don't remember how many bolts, but this was quick and easy). It was necessary to drain the radiator to unplug the hose that connects the top of the radiator to the engine. We had to take off the mounting bolts of the alternator in order to move the alternator enough out of the way. Note, we took the hose off last, so maybe it is possible to get at the front cat without moving the alternator.

Note: to move the alternator, I found a video online that said we needed to take a splash guard off of the front, passenger-side, wheel well in order to put slack on the serpentine belt (AC). I'm not sure why this was necessary. We ended up replacing the AC/serpentine belt because of all of the cracks in it. But I didn't see how this impacted the main drive belt. Anyway, this was done very quickly as the splash guard has 3 bolts on it, and I had to undue two bolts to move the tensioner.

I couldn't believe how much effort was required just to get the exhaust manifold cover off of the exhaust manifold and the front cat.

At this point, we could clearly see everything around the front cat. All of the bolts between the front cat and the exhaust manifold were very hard to remove. *One of the cat's bolts CANNOT be removed without taking off the exhaust manifold*. But to take off the exhaust manifold, it's also necessary to unscrew an exhaust tube (looked like it was for an EGR valve or something) that went out of the exhaust manifold. This was also very large (size 20 or 21 mm open ended wrench was necessary) and very difficult to take off.

And after all that, it was then necessary to undue 3 bolts from below which disconnected the bottom of the front cat from the flex pipe (the flex pipe leads to the downstream cat).

And the rear cat... the Haynes/Chilton manual recommended to remove the downstream O2 sensor only when the exhaust is hot. Well, hot or cold, I could not get the O2 sensor out. Luckily, if you're replacing the lower exhaust and the O2 sensor, you can unplug the O2 sensor and leave it in there. We had difficulty getting this connector off, because it broke when we pushed on the release. Luckily, a small screw driver was used to unhook it (but it was the opposite of what we though).

The rear cat has two bolts in the front which connects it to a short flex pipe and has another two bolts in the back which connects it to the rear flex pipe (which goes to the muffler). The bolts on the rear of the cat were so terrible rusted, there was no way to get them out without cutting them. I initially tried a metal blade in a Saw-Zaw, but it was a complete shit show since I didn't have an acetylene torch.

Putting it together was easy and quick. The biggest issue we had, is that we broke the drain plug on the radiator when we put it back in - next time, I'll just disconnect a radiator house and leave the drain plugs. We used an Easy-Out and it worked perfectly. We bled the cooling system of all of the air and everything seemed fine.

But of course it wasn't. For some reason the alternator wasn't charging the battery. Apparently we didn't clean the terminals well enough when we disconnected/reconnected them. You should always disconnect the negative terminal whenever working on any electrical component (the O2 sensors).

I took some pictures, here is a link to the album:
Replacing the cats in a 2000 Nissan Altima - Imgur

Would I do this again? I would replace the front O2 sensor on my own, but instead, I would buy the parts and bring them to a mechanic to do it... or sell the car. Yeah, sell the car. That sounds better.


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