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How many catalytic converters on 2002 Saturn SL2?

My SL2 has 155,000 miles on it and like most Saturns, it has always consumed oil. Lately, I’ve noticed an exhaust smell and sometimes it takes a while to accelerate. Also, the check engine light has come on. When the codes were checked, it said bad O2 sensor. The mechanics are telling me that the car has 2 catalytic converters - one near the exhaust manifold and another in the tailpipe - but all I can find info on is the one in the tailpipe. Is there one near the exhaust manifold and if so, is it called something else? I did find there are 2 O2 sensors. FYI, I love this car - if I could have bought another one and shrinkwrapped it for later, I definitely would have.

2002 Saturn SL2
Which Engine Is In This Saturn ?

Also, there are different codes for different sensors. Generic Example: P0137 Bank 1, Sensor 2 (downstream sensor).

What specific DTCs (codes) are present ?


Heated Oxygen Sensor
Should Be: One (Sensor 1 - Upstream) Is On The Exhaust Manifold On The Back Side Of The Engine. Sensor 2 Is Farther back, going away from the engine and sensor 1.


Thank you for your answers. I can find that there are 2 O2 sensors - are there also 2 catalytic converters? He quoted me $300 for the one in the tailpipe and $650 for the one near the exhaust manifold.

We’re not all familiar with Saturn models. Do you have a six cylinder or a four? I see the picturenow and you have a 4. I googled it.

When he mentioned the one here and the one there, he was talking about the O2 sensors, not two different converters.

Is The Quote For Converters And Sensors Or Just One Or The Other ?

I can buy sensors for my GM cars for around 50 bucks and the downstream one takes minutes to replace. The Exhaust manifold sensor is a little more difficult to access, but the part price is similar.

(Converters are relatively expensive.)
- Does the mechanic conclude that you have a plugged up converter ?
-Do you have a “flashing” CHECK ENGINE LIGHT ?

  • What are the specific codes ?
  • How much oil does it consume (approximate quarts per mile )?
    This is important as too much oil consumption (not leaks) could lead to the other problems and spoil the replacement of said items.


The SL2 is an inline 4 with dual overhead cams. Its main catalytic converter is in the exhaust manifold. It has two oxygen sensors, the upstream sensor (mounts in the hole in the manifold shown in the photo) which monitors the oxygen in the exhaust stream and “tweaks” the fuel mixture, and a downstream sensor that monitors the performance of the cat converter by providing a comparison signal to the ECU. Only the primary cat sensor is monitored.

The converter in the tailpipe is not monitored and will not trip a light unless it clogs. It will not trip a code for performance of the converter. It will not need changing unless it glogs or rots out.

Good Info, TSM.

I think Karmen needs to get a couple more details from the shop. Also, answers to my questions above would be beneficial for a more meaningful discussion.


There may be one or two cats in your Saturn. The Factory Service Manual (FSM) shows two different exhaust manifolds but both are interchangeable between the SL1 and SL2 engines, one has a canister that could hold a warmup cat (aka pre-cat) or not, the FSM does not mention whether that canister holds a cat or not. The canister is welded to the manifold. The front O2 sensor is in the manifold above the canister. It is in the same place on the manifold without the canister.

The rear O2 sensor, which is a heated sensor is located behind the cat located in the front exhaust pipe. So either both cats are monitored or the canister built into the manifold does not have a warmup cat in it. There is nothing in the FSM for the 02 Saturn that says it has a warmup cat, the only cat it refers to is the cat in the front pipe.

Agreed. Good points all.

OP, the ball is in your court…

Interestingly the FSM refers to the exhaust manifolds as the cast iron or cast iron and stainless steel manifolds.

the same mountainbike & keith, after looking at the exhaust, the pipes do come out and go into a canister. It looks almost exactly like the MagnaCat shown in the link. The mechanic told me the code, but he gave me a couple at the same time so the numbers went in one ear and out the other. But he did say one code was the O2 sensor and the other one was the thermostat, both of which are original to the car so they would not be unexpected. He also let the car warm up & then took it for a test drive, but he said he didn’t notice the lack of power, that only happens every once in a while. He did say the smell is catalytic converter. I know what oil, antifreeze and transmission smell like and this smell is different. It only smells when the car is running - I don’t smell it in the garage.

Check your CV joint boots for cracks. That grease has a different smell and when the boot cracks, it slings grease onto the exhaust pipe. Cats don’t smell, er… catalytic converters that is. Also an O2 sensor and a thermostat would not be out of line for this car at this age, I’ve replace both in my 02 Saturn.

Try to get those codes and post them here. For Saturn specific information, I suggest that you join this forum. You’ll see me there too.

I found the codes on the receipt

there are two cats and a sl2 has a dohc engaine a sl1 or a sl fas a sohc in it

P0128 coolant temp below threshold after specified time.

P0133 O2 sensor 1 bank 1 slow response.

The O2 sensor is a higher priority, this is the sensor in the exhaust manifold so it is easy to get at and easy to change if you have the correct socket. It takes a special socket that has a split in it for the wire. Sometimes you can change it with a box wrench.

The thermostat should be changed pretty soon. Its not as critical right now but it will get worse. In my Saturn, it would set this light at 179°F, minimum is 180°F. I reset it the first time and it took several months to come back, but eventually it did so I changed it. Its easy too.

I changed the thermostat on the Grand Am I had years ago, so feel comfortable doing that myself. Just watched a video on Youtube on changing the O2 sensor and that looks pretty do-able also. Does the rear O2 sensor set off any codes? If there is an issue with the catalytic converter, would that give a code?

There are separate codes for the rear sensor, also codes for the cat. But codes don’t exactly say a part is bad, it says it detected an issue with that part. For example P0420 is cat efficiency below threshold. Replacing the cat as the first step for this code would be a mistake because there are other things that cause this that occur more frequently. This is a case of the cat not working right, but its not the cats fault, something else is interfering with its operation.

In the case of the two codes you have right now, they are pretty cut and dried. More examples would be a P0410 which Saturn’s are prone to is secondary air not working, don’t replace the pump because the problem is usually a passage molded in the exhaust manifold that gets clogged with carbon. A P0507 on a single cam engine for the IAC (idle air control) is usually the intake manifold gasket.

Hi all, My mechanic says I need my catalytic converter replaced 2002 Saturn wagon. My question is, will it be alright to drive for a couple of weeks until I get paid? It is running strong right now. Thanks for any info!

Well, thanks for reviving a 6 year old thread. Seriously, why did you not ask the mechanic that said you need a convertor . Next, start calling independent muffler shops for estimates.