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just keep geting them 01 outback 02 forester 01 outback 99 forester 99 impreza 02 impreza 99 legacy 02 legacy 98 outback 03 impreza all 420 codes in last two weeks i have not been able to track the problem down cats are ok o2 sensers ok cant find what all theese cars have in commen starting to think its a problem with the calabration of subarus ecus to many cars with same codes and no problems any ideas boys ? is driving me and my clientele nuts

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I don't really know the details but I know I do get this code from time to time on my '00 Outback, mostly if it is really windy outside. I've seen it suggested a few times that it's caused by the tight specifications of the EPA (at least in the U.S.). I mentioned it to the garage I go to for inspections and they said they see cars from that era of all makes and models with that code so I don't think it's limited to just soobs.

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exhaust leaks?

 

retarded timing from bad knock sensor?

 

engine temp sensor?

 

 

I bet it's maddening trying to track down all the possible causes.

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exhaust leaks?

 

retarded timing from bad knock sensor?

 

engine temp sensor?

 

 

I bet it's maddening trying to track down all the possible causes.

 

It is maddening. That's why a lot of people turn to the O2 cheater. That's not an entirely legal option for a shop though.

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Exhaust leaks and missing heat shields will cause a loss of heat in the exhaust system and lower the efficiency of the converter. When people install aftermarket headers they tend to throw this code because they don't have any heat shields to keep the heat in.

 

Basically you have to watch 4 things - exhaust leaks, heat shields, O2 sensors (front and rear) and the catalyst condition. One of those always ends up being the problem.

 

GD

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I haven't seen the possible cause of a heat shield or retarded timing before, will have to keep those in mind.

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I'm also wondering about things like a sticking valve or even carbon buildup. just odd thoughts though.

 

so many things can go wrong - or 'drift' in a bad direction on older cars.

 

I'm glad there are folks like Ivan and other mechanics around and I give them plenty of respect. I don't think I'd like to repair other people's cars on a regular basis - I can hardly understand what I'm doing on my own cars.

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I Check for exhaust leaks. Then I check cat temp from front to rear with my temp gun. I monitor the 02, sensors in particular the rear one. The rear should stay above reference voltage, of .5 and not really fluctuate when in closed loop. If it is grossly erratic I change it. More often then not I change the rear 02 as a start of my diag procedures.

 

The rear 02 is just a "cat" monitor so if it is going bad, then the ecu thinks the cat is bad, so it pops the code.

 

Sometimes I have had MAF/MAP sensors and crank/cam sensor contribute to the problem, but not very often.

 

Start with the rear 02 and go from there.

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bett its the heat sheilds i have had to remove many because of under car damage and rusted out and loose so most of theese cars have no heat shields or damaged ones the salt and rough roads kill them quick i never thought it could set codes mabee some header wrap will help keep heat in or have it powder coated or somthing is hard when have no answer for customers

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the $5 spacer is the way to go.

 

the 420 code is such a joke it's not even funny. buy the spacers, install them, and call it good.

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the $5 spacer is the way to go.

 

the 420 code is such a joke it's not even funny. buy the spacers, install them, and call it good.

Unfortunately, the cheaters don't appear to work on MY 05+. Tried one and then two piggybacked. My 05 has 3 cats and 5 O2 sensors. I only have bank one code so that's where I tried the spacers.

That is my experience.

Anyone have success with 05 and later??

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Unfortunately, the cheaters don't appear to work on MY 05+. Tried one and then two piggybacked. My 05 has 3 cats and 5 O2 sensors. I only have bank one code so that's where I tried the spacers.

That is my experience.

Anyone have success with 05 and later??

 

for further diagnostics, could you swap the sensors side-to-side? Might help pin down the problem to some weird burned/sticking valve, odd breather/vacuum issue or bad converter, - vs, a bad sensor.

Edited by 1 Lucky Texan

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i tried a o2 spacer on the 02 forester will use it as a trail car see if it helps i also thought that wraping the o2 in header wrap to keep it hot might help try and keep the heat in

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I've heard that header wrap will hold moisture and dirt against the pipes and rust them out. That might be something to look into if it's going to cause bigger problems than it fixes.

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Unfortunately, the cheaters don't appear to work on MY 05+.

have you already had the recall done for 2005 Outbacks? it may be that you haven't had that recall done?

 

Subaru has revised it a few times, so check for the latest....i think this is an old one and newer updated numbers are available, call your dealer.

 

 

 

NUMBER: WVH-18

DATE: June 2009

 

 

 

APPLICABILITY:

2005MY PZEV Spec. Subaru Legacy and Outback

 

 

 

SUBJECT:

Engine Control Module (ECM) Reprogramming

 

 

 

Introduction

 

Subaru of America, Inc. (SOA) has determined that vehicles affected by this Service Program require ECM reprogramming along with catalytic converter efficiency testing and possible replacement.

 

 

 

Under certain unique driving patterns, such as repeated acceleration and deceleration and/or continuous uphill driving at higher speeds (about 75 mph), the catalytic converters of affected vehicles may develop high internal temperatures that exceed design parameters. If left uncorrected,

this condition may eventually degrade the efficiency of the catalytic converters. (The "CHECK ENGINE" light will illuminate to alert the driver if catalytic converter efficiency has degraded beyond an acceptable level and the vehicle may be releasing air pollutants which may exceed California standards.) To prevent this condition, a modification to the

Engine Control Module software logic has been developed that will improve management of temperatures within the catalytic converters.

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yes but the subaru dealers deny it exists and tell me no reflash avalible but there tech tells me they take the subaru scaner and reset the ecus all the time but they will not tell the public is a big secret round here

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for further diagnostics, could you swap the sensors side-to-side? Might help pin down the problem to some weird burned/sticking valve, odd breather/vacuum issue or bad converter, - vs, a bad sensor.

Swapped downstream sensors side to side. Cleared codes and just rescanned after a day's drive and 420 is now pending. Safe to say not the sensor...

Car runs very well. I don't hear any exhaust leak and don't know how to check for burnt valve. As I said, the car runs great.

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Swapped downstream sensors side to side. Cleared codes and just rescanned after a day's drive and 420 is now pending. Safe to say not the sensor...

Car runs very well. I don't hear any exhaust leak and don't know how to check for burnt valve. As I said, the car runs great.

 

does it show the same side? If so, what about swapping sides with front sensors?

 

also, does the scanner you're using have freezeframe data? fuel trims are also broken down by banks (IIRC) and if one bank's trims are are a lot different, could point to a bad plug or injector if the sensors aren't the problm.

 

sorry, all I have is speculation to offer. But converters are expensive and more experienced folks than me all say the converters are sturdy so, it's worth saving that as a last ditch approach.

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I already replaced Bank 1 front sensor so that is out of the equation. Now having swapped the downstream sensors, that also is eliminated from the diagnostic tests.

Don't have scanning ability for trim.Not giving up yet but...

There are aftermarket cats at 1/3 to 1/2 the price and variable optional warranties as compared to genuine soa.

http://www.autopartswarehouse.com/search/?N=0&Nr=AND%28wpn_tl_name:Engine+%26+Drivetrain,wpn_cat_name:Catalytic+Converters+%26+Components,wpn_scat_name:Catalytic+Converters,part:Catalytic+Converter%29

Any experience with this company?

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I already replaced Bank 1 front sensor so that is out of the equation. Now having swapped the downstream sensors, that also is eliminated from the diagnostic tests.

Don't have scanning ability for trim.Not giving up yet but...

There are aftermarket cats at 1/3 to 1/2 the price and variable optional warranties as compared to genuine soa.

http://www.autopartswarehouse.com/search/?N=0&Nr=AND%28wpn_tl_name:Engine+%26+Drivetrain,wpn_cat_name:Catalytic+Converters+%26+Components,wpn_scat_name:Catalytic+Converters,part:Catalytic+Converter%29

Any experience with this company?

 

 

maybe call a coupla parts stores. My Innova scanner is around 8 years old and it will capture FF data. maybe the scanner at you local parts store can get the fuel trim data.

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i'm realy thinking that the 02s need to be insulated to keep heat in the senser i wonder if some chevy spark plug wire boots over the o2 may help

Insulate the sensor?? whoa now that's a whole new line of reasoning. Not sure I follow but I'll let this discussion continue.:horse:

To answer an earlier question, I did have the ecm reset done at 57K miles. this guaranteed the cat to 100K but I threw code first at 105K DRATS!:banghead:

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i'm realy thinking that the 02s need to be insulated to keep heat in the senser i wonder if some chevy spark plug wire boots over the o2 may help

 

Shouldn't make any difference. Sensor tip temperature only need be over about 600* F to operate correctly. Which should be easily obtained since the sensor has it's own insulation and heating element internally. I've never encountered an externally insulated sensor and in any case if the sensor wasn't reporting or the heating element was bad then that would set different codes - not the 420 code.

 

GD

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