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Discussion Starter · #1 ·
I have a 96 OB with a CEL on. Ran the codes on the car quite a while back and got the one for the catalytic converter. The car has recent plugs and wires as well as O2 sensors. When the CEL is erased it comes back on after 15 ignition starts. Is this most likely the cats? I have no problem replacing them (about $300 for both at rock auto) but I'd rather not if it could likely be something else.
 

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2005 OBW 2.5L, 1989 Subaru Justy, RIP Blu
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Did you use OE O2 sensors?
Exhaust leaks can cause an O2 light.

If those are Eastern Cats, don't get them, they are troublesome products and get them from another source.
 

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Discussion Starter · #3 ·
I was going to use the eastern catalytics but they also carry Bosal for roughly the same price. I don't know if the O2 sensors were oem. I'll try to find out since it's my girlfriends car and she had them done in Oregon before she moved here.
 

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01 VDC, 05 R Sedan, 06 BAJA EJ257
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OBW H6 VDC, Tribeca, XT6
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Converter is most likely fine.

Finding the cause is tricky, I don't know that anyone on here...or anywhere online for that matter, knows how to track it down consistently other than cardoc.

If you replace the cats without finding the cause then you have the chance of it coming back again...maybe sooner rather than later with lower quality aftermarket parts, and subaru converters are insanely priced.

I would do the $5 spacer fix before replacing the cats. Buy one off ebay. I've posted lots of links to them before.
 

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1998 Outback wagon, 5 speed winter package
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I used Denso (they make the OEM ones from my understanding) O2's with NO problems. Chances are they used an off brand or NON direct fit to save a few buck and charge full price. Or it could simply be an air leak prior to the O2's. Check all bolts for tight. When I bought mine i had a manifold bolt missing and the others were loose. tightened them and the CEL went away. It returned some time later but for a different reason. I replaced my cats with Magnaflows with no issues.
 

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2005 OBW 2.5L, 1989 Subaru Justy, RIP Blu
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Its not unusual for the exhaust manifold gasket to leak with age. Also a cheao vacum gauge will tell you the condition of the cats engine and exhuast.
 

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'97 Outback Limited, 2.5 DOHC, Automatic, ABS
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Trying to keep this short. I'm the CEL is on guy in the shop. Below is what I look for when it's P0420. Unless you have an exhaust leak upstream of the downstream O2 sensor, P0420 is a dead cat. It is rarely due to a bad downstream O2. You need a scanner that does live data, and updates the screen at least twice a second. Here's what to watch. Start the car, both upstream and downstream will read around .45V. As the car warms up, in about 30 sec, the upstream starts to "swing" from .1V to .9V. Soon after the downstream starts to do the same. This is where you watch for O2 health. They should be changing, the highest most of the time is around .75V to .15V. Actually, the lower the downward swings are the healthier the sensors are. The car should be in closed loop with a minute. That means the upstream O2 is alive and the computer is using it to control the fuel. My car is in closed loop in 25 sec from a 40 deg start. Here's where the computer starts to watch the cat. From a cold start, a minute to warm up, then drive a mile or so, the downstream O2 (B1S2 on the scanner) should stop the wide swinging and vary from .4 to .7 and with another minute be pretty steady around .7V. This is a healthy cat. These engines shut the injectors off when you coast and the tach is over 1300 RPM. Now they call it PZEV.....when you are coasting, the front O2 instantly drops to 0V, and about a second later the downstream. As soon as you get back on the gas, or drop below 1300, the downstream should climb back to .7V. If the downstream is always swinging, the cat is dead. If it's only flat at idle, the cat is dead. Sometimes it's only flat at a steady speed, it's dead. This is what the computer looks at to if it should throw the P0420. Again, unless you have an exhaust leak, P0420 means dead cat. 99%.
Does stuff like Guaranteed To Pass Emmissions, Lucas or Techron clean a cat? Yes, if it's borderline. What kills a cat? Cheap gas, to much short trip driving, oil burning, never changing the oil so now the rings are gummed up (Penzoil high mileage works wonders over a few thousand miles) , head gasket leak, running to rich "cuz the the thermostat is running too cold, running premium gas and doing short trips, and driving with skip for more than a couple of days. The upstream O2 is tired and running rich. Stick with gas that claims to clean the engine. Shell, Mobil, Irving, Conoco, BP. Use a can of Techron at every oil change. Techron is safe for the Nissan injectors. Use Shell VPower when you are going to be on the highway for the weekend, it's got Techron. Hope this helps, S
 

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Stella501,

Some of what you post is correct. Out of a few hundred P0420 codes I get on several makes and models through the year, I replaced 3 converters last year. The others, the converter was not the issue. I have even corrected an issue with the engine and the rear waveform went away. You find why the converter is not performing, you will find an issue with engine performance. IF the CAT is bad, you still need to find what killed it. Its all in temperature and combustion control.

http://www.subaruoutback.org/forums/66-problems-maintenance/49537-p0420-diag.html

http://www.subaruoutback.org/forums...spective-p0420-catalytic-efficiency-code.html

https://www.youtube.com/watch?v=MVi4wI6F7Ik

https://www.youtube.com/watch?v=pl2p6uE6ODM This one is running E85 and programmed for it

https://www.youtube.com/watch?v=wwrnyTvGaPU and after https://www.youtube.com/watch?v=agp8cptYWgQ
 

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Discussion Starter · #12 ·
Here's what I've done so far. I don't have a scanner that can read live data (just using Torque 2 with a bluetooth obd2 adapter) so I checked the codes and got the one for the rear o2 sensor, the cats, and the egr ( 420,400, and 136? maybe? not sure if that last one is right, it was a month ago.) and since then I cleared the codes, replaced the rear o2, had the valve cover gaskets done (that was just to eliminate the worst oil leak and clean it up so the rest of them can be tracked down), and replaced ALL of the vacuum lines and that little foam disk pressure valve thing. Also I used a vacuum tester on the egr and it moves freely and easily. So far the codes haven't come up again but I know it sometimes takes a while after clearing them before they return (15 starts I think) and the car only gets used about once a week. Oh and I also replaced the pcv valve.
 
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