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Help deciffer Code for CEL........ P0420

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I've a 1995 Legacy L. Sedan (2.2 I think).

I need a oxyen sensor, where to buy online? My car was runing very good, but yesterday I put a little sea foam in the gas tank and today I got the "check engine light", could that damage the oxegen sensor? I last change sensor 3 years ago. There is a slight hisitand when I first start off in the mornings and I saw a little bit of carbon in the sparks plug wire, so I change the sparks plug, but couldn't get any wire at my local stores. Still has the hisistant so I put a little seafoam in the gas tank. I merely trying to tune up before winter, but may screw things up, did I?

How often should I change coolant sensor? Do they have car manual in ebooks?

I can tell you this from experience, you MUST pull that check engine light code before you go and randomly start replacing sensors.

 

As for purchasing a new sensor, you have several options. You can just go to Discount Auto Parts and buy a new sensor that plugs and plays. Or if you're feeling industrious, you can buy a univeral 4-wire oxygen sensor from www.oxygensensors.com which will allow you to splice the ground wire for the sensor into the ground for the sensor heater, which will give you a better reading and a possibility of slight performance and mileage improvement, plus the universal sensor will be cheaper.

 

But pull the code first. Really the SeaFoam shouldn't damage your O2 sensor, many people have run all kinds of engine cleaners through their cars with no ill side effects.

  • Author

I've Advance autoparts in my city and they don't have much in terms of senor, sparks plug wire etc.

Can I pull the code my self? I'm very technical and mechnical, but I don't have much tools? Is it too complicated to install a universal senor? What's the difference between universal and oem parts?

I wouldn't change the Oxygen sensor just yet. Check and clear the codes first. We use Sea Foam in our shop (municipal shop with 500 vehicles), and I've had the CEL illuminate after a treatment. I've yet to see a damaged sensor.

I've Advance autoparts in my city and they don't have much in terms of senor, sparks plug wire etc.

Can I pull the code my self? I'm very technical and mechnical, but I don't have much tools? Is it too complicated to install a universal senor? What's the difference between universal and oem parts?

 

Call Advance and ask them if they can pull the codes. Most of them can pull the codes for free.

 

Keith

  • Author

Advance Auto Parts pull the code for me late this evening.

 

DTC (Codes)

 

P0420

Catalysis Efficiency

Below Threshold

(Bank 1)

 

What this means? I hope no damage to the catalyst.

 

I use Seafoam within a week after Redline. Maybe another tank of gas will flush them out of the fuel system.

  • Author

I found a ton of articles on google that seems to convey that I have a bad cat.

 

I'm curious to know if I mess my good running car up by using the bloody seafoam and Redline fuel treatments. Also I change the sparks plug (bosch) 3 weeks ago.

What's the going rate to replace Cat.

  • Author

I reset using the battery info. on this site. The CEL light is off and I refill the gas tank and drove 30 minutes at 70mph. The good Lord is faithfull all the time!

Good to hear, although I'm not sure that solved your problem :(

 

If it comes back on, yes you might be due for a new cat. I'd try some p&p yards to see if they have a good set of exhaust manifolds you can swipe.

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