Hi guys and gals,
I've had the P0420 code almost since buying this car used, and it's finally come time for inspection. I've been reading many, many different threads on the topic here, but I'm having a hard time keeping track of all of the different responses, solutions, and what worked and what didn't.
So: if you have had the wonderful error light come up that suggests a replacement catalytic converter, what did you do? Was it a leak somewhere? Was it a bad part (O2 sensor, etc)? What ended up fixing it?
I'm trying to consolidate everyone's experiences into one thread for my own benefit, and hopefully others who encounter this wonderful problem down the road can use this to help them out as well.
Oh, and for the record: when I took this in to get the code read last year, the shop acknowledged that it's often not actually the converter that needs replacing, and that even if it was, it's not really hurting the car except for halting an inspection pass. So that's their current stance on it...
How about dealing with the fact that people are spending huge dollars on chasing their tails through repair shops and still getting the codes! no other cars seem to have this perpetual problem.
It is reminiscent of the head gasket melt downs, or do you think those were ok too?
Read the link I posted and do a google search. Lots of other cars get the P0420 codes and have trouble resolving them.
At 240K, it is entirely possible that your catalytic converters(s) need replacing. They do not last forever.
But the only way to know is to do a thorough diagnostic as outlined in the link I posted. If you don't have the tools or the knowledge to do that, be prepared to pay someone who does.
Right on, troubleshooting is a must. Yes the cats may have reached the end of their useful life with that much mileage. People who get things replaced at a shop and then still have issues I don't see how that is Subaru's fault, to me that is the shop's fault for not fixing what was causing the problem.
This thread has made for some interesting reading since my 01 OBW is reading this same code indicating the catalytic converter is bad. The problem is this is the second one in a matter of about three years. I am the original owner and I have roughly 93K on my OBW right now and I believe the first replacement was around 50K. The cost of the repair will be huge. I've got a few other thoughts and issues but I'm not sure this is the thread to post them on so I'll keep looking.
Had my front O2 sensor replaced on 99 outback and 0420 code cleared. After 25 mile drive to work, no CEL. Had car smogged at lunched and passed. Very happy about this because reg is due and I did not appreciate the estimate of "1800" for cat converter.
I just got a recall notice from Subaru for this. They replaced one of my catalytic converters and re-programmed something...my car is a 2005 Outback 2.5i wagon. It might pay to call and find out if your car should be repaired under this recall.
I only get this CEL if I push RPM's high in 5th gear (meaning, if Im speeding) its happened 3 times now when Ive pushed over 80mph. but it does go away after a couple of days.
it doesnt happen in any other gear, just 5th. I thought it might be some way Subaru was trying to keep people from speeding too much. :14:
This is true. My girlfriend used to have an '02 Corolla... she had 3 different converters, new 02 sensors, valve guide seals replaced (shop thought the oil burning was fouling the cat), and still, PO420.
Thankfully she was able to cut her losses and get rid of the car, which was a nightmare from day one. Now she drives my former ride, a '95 Legacy which now has 155K and no major problems!
I can't help but wonder why this seems to be such a common issue. Are the sensors on newer cars overly sensitive? Are the parameters of acceptable operation too tight? Do some gasoline blends contribute to less efficient engine running, therefore slowing the warm up of the converter?
My independent Subie mechanic theorizes that poor quality gas, and some of today's newer gasoline blends can contribute to poor running, hesitation, random misfires and CEL codes. I think there is an element of truth to that. I've stopped getting gas at a certain well-known central PA gas station chain because my car just ran like crap, on more than one occasion, after filling up there.
I thought I would add my experiences ...very simple...added gas to a near empty tank..a few minutes later going down the highway the CEL comes on (po420)..next full tank at a different gas station, the CEL disappears shortly after filling up...the car has about 100,000mi/..front o2 sensor has about 60kmi/ rear o2 sensor is original
Here is some good info I found online. For continuously rich O2 sensor readings:
1. Check the fuel pressure. High readings will cause rich conditions.
2. Leaking injector(s) will cause rich exhaust.
A leak down test and/or a power balance test can usually reveal the leaker.
3. A contaminated or malfunctioning canister purge system can very easily put uncontrollable amounts of fuel into the intake manifold. Simply disconnecting the vapor hose can reveal this as your problem system.
4. Check vacuum to voltage readings at the MAP sensor. A low MAP output will cause a rich ecu reaction. (Don't forget vacuum readings again!)
5. A false tps signal can cause the system to go rich if the Ecu sees a high tps output. Check tps readings at idle and for a smooth rise to wide open throttle.
I have replaced everything, nipper said to replace front sensor with oe, just did. Still reads rich. I have no vaccuum leaks or exhaust leaks. Checked fuel pressure last night and it reads alittle high. Factory range is 30-34psi at idle. I have a reading of 36psi. I have a stumble at idle, pulled spark plugs and noticed one plugs was black. I have new injectors on order from subaru and wont get until tuesday. I will advise. A bad map sensor could cause a p0420. I have the guys a dealership helping me.
Has anyone looked at there tailpipe? Is it really black?
Ill figure it out, its all I think about lately.
People with scan tools, what reading are you getting at idle from front and rear sensors? Here is the website so you can understand O2 sensors. Diagnosis Using The Oxygen (O2) Sensor
Subaru has just replaced my front CAT and sensor at 45000km (28 000 miles). Looks as if these damned things can be as sensitive as all ****, as the CEL came on in the Forester I had as a loan car whilst mine was off the road....that's done 100 000 km = 62000 miles.
04 OBW. I took out my EGR and PVC and cleaned them with some carb cleaner. My OBW used to have a rough idle when the check engine light was off and A/C was on. The CEL has been out for a few days, but the significant thing to me is the idle now sounds normal with the A/C, so hopefully that is all I'll have with this issue. LOL I'm sure I will post in a few days when the light comes back on...
hey guys, now I know why there are some many O2 sensors for sale on ebay. Any way, I just got an 02 OBW limited 2.5l with 149k miles on it. Didn't pass emissions because CEL bulb was burned out and had a p0420 code, sucky. Had the bulb changed, and I guess the emissions guy cleared the code because my shop never saw it, even though I told them about it, but got the car back, no CEL was going to get emissions checked and CEL light came on. Took back to shop and same code p0420 again. They, obviously, came to conclusion that it needs a new cat. Am thinking I should just go ahead and drop the $ to get that out of the way and have new o2 sensors installed. Yes it's expensive to replace the cat( aftermarket one), but shop will do it for parts and labor for 800, which is far cheaper than dealer cat. Does this sound like a decent plan? should CEL go away after this? Starting to question my purchase, but I DO enjoy the car, and trust Subaru's reliability, this one problem seems to plague ALOT of others though.
Thanks for all the other postings, they've helped in informing me about this problem though.
I bought my 01 obw limited 188k mi 10 days ago, everything was running fine. Drove 150 miles over the weekend and the cel came on. Went back to the lot I bought it from and their mechanic read the P0420 code and said needs a cat converter. Ok they put one on, I picked up car next day drove 20 miles and the light came back on-same code & problem! Dealer said I'm on my own. Found this forum and got lots of ideas. Checked air filter , cleaned throttle body(neither was dirty). checked pvc valve then pulled spark plugs. plug was very worn down but still burnig clean, (all 4 were light tan as normal, no carbon) I put in a new set of NGK platinums, reset codes with my reader. Light has not come back on yet-100 miles so far.
I think just keeping car in tune and cleaned up will take care of most of the P0420 problems. Their mechanic said I needed to replace the other 2 cat converters, and was flabergasted when I told him what I did to fix it!! I was glad it was their money they wasted not mine! Go Subies!:29:
It sounds like you've taken proper steps to resolve the issue causing the engine light to come on again. However, keep the following in mind.
When a code is cleared, the emissions systems monitors are also turned to not ready status. It takes a specific drive cycle to return the monitoring systems back to ready status and the whole time the monitors are off they are not monitoring the emissions control devices. This is why sometimes a code can be cleared and not come back for weeks. Until the monitoring system is back to ready status the ECM doesn’t know about a device or a condition.
My CEL is coming on now. (2004 OB Wgn, 2.4l auto, 64K ). I am told it is a cat converter problem P420. I was told by the muffler shop it should be covered under Subaru warranty 8 yr / 80 K miles. Just putting this out there as perhaps some of you may be covered also. I personally believe the 10% ethanol in the gas these days is the primary culprit of this issue.
I learned over this summer that P0420 is often caused by a spark plug wire needing replacement, not just in Subarus. My CEL came on and went off by itself.
Can anyone tell me the specified resistance that the spark plug wires are supposed to have? So far I have only read #1 at 3200 Ohms. Seems I will need to remove battery, w/wiper tank, air intake elements to access #'s 2,3,4.
I learned over this summer that P0420 is often caused by a spark plug wire needing replacement, not just in Subarus. My CEL came on and went off by itself.
Unfortunately, that information is incorrect. P0420 is related ONLY to o2 sensor readings, which are used to determine the catalytic converter efficiency.
The rear o2 sensor only exists to measure the difference between its reading and the front o2 sensor reading. If that difference is outside of a certain parameter, the ECU thinks the catalytic converter isn't working properly and throws P0420. Great system -- as long as the o2 sensors are working 100% properly. If they are not, a failing o2 sensor reading will cause a false 'bad catalytic converter' code. Hence why techs plug scantools in and watch the voltage of the front and the rear o2 sensors to determine if they are working properly. If they are, it's a bad cat. If they're not, the behavior of the voltage readings will determine which o2 sensor is failing.
Here is a new one. P0420 comes up 3 weeks ago after I changed the spark plugs then self clears then comes back a day later. I think i can hear an exhaust leak? I get under the car and remove the heat shield, "Holy $&!t" the weld on the collector chamber is shattered. What on earth would cause this? I have not been off road in months, we have had some rain but my engine temp has never been high. I am baffled and off to the dealer. There is 95,000 miles on the car, it is an 07 OB 2.5 basic. Glad I shelled out for the extended!
This is a great thread. Everything in one spot!
2002 Outback
2.5
151,000 miles
CEL – P0420 has been a problem for a while now. Dealer said I needed a new CAT after only reading the code. Cleared the code and it stayed off for a few months. Code came back and I brought it to my local mechanic who did some testing and said I needed a new CAT. Had the CAT and rear O2 sensor replaced w/aftermarket (he said the front was still good and he was able to salvage it). This was 1-1/2 years ago.
Code cleared and stayed off for a while. It started to pop up again. I would clear and it would go away for a while. It seemed to come up only after some spirited highway driving (80 miles running around 75 or 80 mph).
The CEL and P0420 has started to come up more frequently again. I have replaced:
-PCV – subaru
-Spark plugs – NGK
-Plug wires – subaru
-Fuel filter
-Front O2 sensor - subaru
I just did the front O2 sensor 2 weeks ago and the CEL came back on w/P0420. The only problem I had w/changing the O2 sensor was the clip that holds the wiring harness together snapped. My solution was to tape it together w/electrical tape.
Questions:
• Do I need to have the retaining clip to hold the wiring harness together? It is plugged in and seems tight, but I guess I could be wrong.
• I have not disconnected the battery, removed the heat shields in front of the CAT to look for leaks (I don’t hear any), disconnected the battery or done more than a cursory spray w/carb cleaner on the throttle body (but it didn’t really look dirty). What would folks think I should look at next?
An aftermark one is not terrible, but unfortunitly most of them go to Eastern which is garbage.
Why hasnt the rear O2 sensor been replaced, they are cheap enough, and should have been replaced with the cat.
Use a vacume gauge, this will tell you if there is a problem with the cat (clogging which is how they fail).
A exhaust leak anywhere before the cat will cause the code.
Would it come on during deceleration cruising, or on deceleration (lifting your foot off the gas). These are important clues.
How does the car sound when starting cold as opposed to being started warm. Have someone else listen as you may be used to it.
Just chaining parts really is not an answer nor a clue. You need to take readings on how they are performing using a volt meter. You may be needlessly replacing parts.
Thanks for the response Nipper.
Sorry, the rear O2 sensor was changed with the cat.
I will pickup a vacuum gauge. Probably makes sense to have so I can rule out leaks anyway. Do you know what a normal reading is for this car (2002, 2.5L, AT)?
The parts that were replaced were done because it they were needed for a general tune-up. I was guessing that I needed a new front O2 sensor since it was original and the car has 151,000.
I will plan on pulling the heat shields off the y pipe and checking for an exhaust leak.
I will also pay attention to when the light comes on again.
The car does sound loud (I think piston slap) when starting, but it quiets down after warming up. I don't hear exhaust sound. Is there something else I should be listening for?
I got my 01 OBW over 3 yrs ago. I got it cheap from a private sale b/c the dealer told the folks the 0420 code it showed at one time meant it needed a cat replacement. (It also had the crackly paint job problem.)
The CEL light went off and on intermittently for the first year or so I had it. I haven't seen a CEL light for a year now. I have not done any work on the car (related to CEL codes) and it has been running great.
I bought a 2002 2.5 Outback with 240k on it with all kinds of things wrong with it. One was the P0420 code. The dealer had looked at it and recommended a new catalytic converter. First I cleaned all the air intake lines/hoses and replaced the PCV, then replaced the front O2 sensor, and finally bought a used cat with 85k on it. That did it.
Final solution, new cat (well used with 85k).
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