2006 Volvo V70 CEL with Code P0420

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The 2006 Volvo V70 just had the Code P0420 last night. Cleared the code for now before my daughter drove it to school today.

According to engine-codes.com these are possible causes:

- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM)

What do you guys think I should try first ?

Use a bottle of Chevron Techron Fuel System Cleaner.

Check and replace spark plugs if needed ?

How do I check "Intake Air Leaks" and "Fuel Injector Leaks" ?
 
According to engine-codes.com:

"The P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem."

I would like to first try easiest/cheapest fix(es) and if it didn't fix the problem then if O2 is needed to be replaced I will, and if it didn't permanent fix the problem then Catalytic Converter. Catalytic Converter for California is very expensive.
 
Nothing; Unless you did some specific work very recently, the light is coming on because the converter efficiency has finally dropped form say 90% to 89.9%. It is a slow and stead process. Look at the Mode6 data to see how badly the ECM flunked the catalytic converter test. Right now it will be on the border line. But it will only get worse.

Either change the converter (use OEM) or research in to anti-fouler aka sensor extender.

You can also try few snake oil remedies and some of them may extend the time between lighting up of the P0420 code. By the way, it will take a while before P0420 will start becoming persistent. So any remedy that you try and if the light stays off does NOT imply that the remedy actually worked. It is long drawn out process.

If anybody tells you to replace rear O2 sensor to fix P0420, he is an idiot regardless of his ASE credentials. Learn the theory behind the P0420 code and then you will understand why replacing rear O2 sensor to fix P0420 is one of the stupidest thing to do. You actually want a rear O2 sensor which is sluggish and degraded to prevent P0420 from turning on. The extender moves the sensor away from direct flow and the the sensor reads less and the ECM thinks everything is fine. You want fast acting front sensor but slow and lethargic sensor on the rear. Yes, it is simplistic explanation but should be good enough.
 
If you notice strange idle when cold or unusual idle it might just be an intake gasket leak. Id check that first before swapping 02 sensors. Start your car, and spray carb spray around the intake and see if any change in engine sound. Good way to test it. 8$ gasket cheaper than 02 sensors.
 
The cold idle sounded normal this morning when I started the car and drove around a block. The CEL was off but I hooked up the scanner and it showed P0420.

I will add a bottle Techron fuel system cleaner later today, the car didn't have any fuel additives for more than a year and test the intake gasket leak.

If the code P0420 came back after verify that no air leak I will then check the spark plugs, and after that will try O2 sensors.

The Volvo has only 16x,xxx miles and less than 10 years but gave me more headaches than 370+k miles 21 years old LS400.

PS Thanks guys, I think I will be able to fix this problem with your helps.
 
Last edited:
Originally Posted By: HTSS_TR
The cold idle sounded normal this morning when I started the car and drove around a block. The CEL was off but I hooked up the scanner and it showed P0420.

I will add a bottle Techron fuel system cleaner later today, the car didn't have any fuel additives for more than a year and test the intake gasket leak.

If the code P0420 came back after verify that no air leak I will then check the spark plugs, and after that will try O2 sensors.

The Volvo has only 16x,xxx miles and less than 10 years but gave me more headaches than 370+k miles 21 years old LS400.

PS Thanks guys, I think I will be able to fix this problem with your helps.


Agreed.
 
Originally Posted By: HTSS_TR
The cold idle sounded normal this morning when I started the car and drove around a block. The CEL was off but I hooked up the scanner and it showed P0420.

I will add a bottle Techron fuel system cleaner later today, the car didn't have any fuel additives for more than a year and test the intake gasket leak.

If the code P0420 came back after verify that no air leak I will then check the spark plugs, and after that will try O2 sensors.

The Volvo has only 16x,xxx miles and less than 10 years but gave me more headaches than 370+k miles 21 years old LS400.

PS Thanks guys, I think I will be able to fix this problem with your helps.


I know this may sound simplistic, but could the car be driven more? In my experience with Volvos (9 so far in my family) the more they are driven the lower the operating costs - not on just per mile cost but total cost. I just completed a comprehensive maintenance update on the 93 245 my parents gave me with 78k. It cost me about the same to base line this car as it did to run my 89 740 for 336k. (Not including wearables.) My 07 V70 has 120k with very low per mile costs; slightly higher than our Honda CRV. I really think you'll help yourself by driving the car more.
 
Originally Posted By: Vikas
Nothing; Unless you did some specific work very recently, the light is coming on because the converter efficiency has finally dropped form say 90% to 89.9%. It is a slow and stead process. Look at the Mode6 data to see how badly the ECM flunked the catalytic converter test. Right now it will be on the border line. But it will only get worse.

Either change the converter (use OEM) or research in to anti-fouler aka sensor extender.

You can also try few snake oil remedies and some of them may extend the time between lighting up of the P0420 code. By the way, it will take a while before P0420 will start becoming persistent. So any remedy that you try and if the light stays off does NOT imply that the remedy actually worked. It is long drawn out process.

If anybody tells you to replace rear O2 sensor to fix P0420, he is an idiot regardless of his ASE credentials. Learn the theory behind the P0420 code and then you will understand why replacing rear O2 sensor to fix P0420 is one of the stupidest thing to do. You actually want a rear O2 sensor which is sluggish and degraded to prevent P0420 from turning on. The extender moves the sensor away from direct flow and the the sensor reads less and the ECM thinks everything is fine. You want fast acting front sensor but slow and lethargic sensor on the rear. Yes, it is simplistic explanation but should be good enough.
The California smog troopers, I suspect, look for such things. They check for "CARB approved" exhaust parts with an under car inspection. It's why "49 state" parts are cheaper in many cases and can be used on California sepcification cars not registered in the state.
I do agree, the the downstream sensor is the ""quality control" sensor, though, and the ECU feedback loop operates on the "front sensor(s). You could install a 49 state converter, which would work and be cheaper, BUT you'll probably be caught by the inspectors (unless they find a Franklin on the floor) I don't suggest doing it at all.
 
I'm told by my California friends that there may be an unofficial "bounty" on non-CARB parts. They look at "performance cars" closely.
 
Hello, This thread caught my eye because I drive a 2002 V70 w/181K. IS YOURS A TURBO OR NOT?
I've gone to the links and did a P0420 search. It seems to be all here except one thing from a crack-pot I love.

Sure you can't go wrong with a bottle of Techron (before a stint of local driving).
Yes, spray carb cleaner around the intake hardware to check for leaks.
Absolutely check the plugs.
Try the extender if "they" won't haul you away to the CaliPollutionPokey.
BUT Scott Kilmer made a video claiming a soaking of the converter in soapy water can clean 'em out occasionally.
Crazy I know but since replacing the converter is so dang expensive AND replacing the rear sensor seems to be the last thing you need to do-sluggish rear sensors are OK (from post I found)-maybe it's worth a try?

I do not recall if the rear sensor is heated or not. If so, could a faulty heater circuit cause this code? Kira
 
Originally Posted By: Kira

I do not recall if the rear sensor is heated or not. If so, could a faulty heater circuit cause this code? Kira

There are OBDII codes for failed heater circuits. That in mind, it might only appear if the sensor develops a short or open circuit. Sometimes an O2S can fail just enough to hurt engine performance, but not enough to trigger an error code.

This is why I would look at replacing the upstream O2S and possibly the downstream one.
 
Originally Posted By: Astro14
Try Techron if you like, but this is a common Volvo issue. Converters are over $1,000. Spacing the sensor is the first thing I would try.

This is the simple fix:
http://www.ipdusa.com/products/8656/109553-oxygen-sensor-spacer-cel-boss

Try this first, before going after everything else.

We need smog test every 2 years, anything not CARB approved will not pass, the smog technician checked everything carefully the last few times I had my cars there for smog test. Also, my V70 is non-turbo and doesn't have high flow cat.

Thanks for your recommendation.
 
I would try spacing the O2 as has been suggested. It is very hard to see under the car for the inspection, not saying it is ok, but they won't catch it most likely.

Luckily my R car never had an issue with it, but I did have an offroad downpipe ready to put on and it had the spacer already built in.
 
Get a scanner (or equivalent software/hardware) with data logging capability and monitor the front and rear O2 sensor readings. If you find that rear O2 sensor starts switching fast and mirrors front O2 sensor, your catalytic converter is done and needs to be replaced. That is how computer triggers the P0420 code.

If you go the spacer route, by the time your smog check is due, the spacer would have become pretty much indistinguishable from the O2 sensor.

I suspect after Techron, you might have few weeks where the code will not fire up but eventually that is not going to work.

I have gone through this with three of my vehicles and it took months/years before coming grips with this code. I can unfortunately now in a position to say that I have at least 10 years of experience in battling with P0420/P0430 codes.

I have not tried current snake oil remedies such as acetone, Cataclean etc but if they were available at that time, I would have given them a shot.
 
Thank you all for your suggestions/recommendations.

I will reread all recommendations and will decide which steps I will take to tackle the P0420 code. I will think about benefit/liability of the O2 sensor spacer. It seems to be the cheapest and easiest route, but I hate to have the smog technician points to the illegal part in the emission system and fail the smog test.

I have a basic OBDII reader/scanner and Ultra Gauge, I don't know if either one has data logging capability to monitor the front and rear O2 sensor readings.
 
If you want to know what's going on with your Volvo, you need to find someone with a copy of VIDA (you can get the Chinese version for about $100) and the DICE interface. Dealer has it, of course, but most independant shops don't.

Generic ODB II doesn't get you far on this car.
 
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