My 2000 Corolla's check was on, and sent to the dealer, here was the
Access ECU, Locate DTC P0420 for catalyst below efficiency
Diagnose catalytic oncverter internally worn
new catalytic converter and oxygen sensor installed $1530.78 plus tax
Front motor mount worn $219.55
Here are my questions?
1. is "P0420" the diagnose code for the problem?
2. Do catalytic converter and oxygen sensor have to be replaced
together? They were replaced around 33000 miles during warranty, now
the car has 139000 miles on it, what is average lifetime for those
3. what is "Front motor mount worn", does it have to be replaced?
My car just passed PA inspection two weeks ago, and I like to continue
to drive for antoher year before next inspection, then get rid of it.
Is it safe to drive my car without any fix?
Thanks a lot.
When the check engine light comes on, the car's computer usually stores a
trouble code. Code P0420 means that the catalyst sytem's efficiency for
bank 1 is below the proper threshold. The Corolla has an in-line 4 cylinder
engine so there is no bank 2 (unlike an engbine with a "V" or horizontally
opposed configuration). Basically it means that the system thinks that the
catalytic converter is not working efficiently. The catalyst in a catlytic
conver does not wear out but it can become coated with contaminants over
time so that the catalyst can't work on the gasses passing over it.
The catlytic converter and oxygen sensor do not necessarily have to be
replaced together. An O2 sensor that is marginal could give the same
trouble code so the shop is probably covering all possibilities as to the
source of the trouble code.
If good quality gas is used, a catlytic converter should theoretically last
the life of the car. An O2 sensor's life can be anywhere from 60,000 miles
to the life of the car.
I believe that cheap gas can shorten the life of the O2 sensors and catlytic
converter, which is why I try to stick to name brand gas. It helps to get
the exhaust system good an hot every so often by taking it out on the
highway in 3rd gear for a few miles.
The engine is attached to the chassis in 3 places with a rubber block. The
rubber block allows the engine to flex a little and dampens the engine
vibrations that are transmitted to the passenger compartment. The rubber in
the mount sometimes becomes hardened or cracked. This is not a common
problem in Corollas and I would not worry about it unless you get strange
noises when accelerating or shifting from acceleration to braking.
correct the return address punctuation to reply
Thanks a lot, Ray.
What is "sytem's efficiency for bank 1"? I was asked by an exhuast
repair shop for upstream or downstream O2 sensor, which one they were
asking about? I may have them replaced by an exhaust repair shop like
Midas instead of dealer. The other thing is that I am not that handy, I
can do some simple maintainance work, like oil change, front brake
replacement, but how difficult to replace them by myself using after
The O2 Sensors are parts that you can replace yourself, so to answer your
question, yes, you can take the car to a muffler shop instead of to the
The O2 Sensors are generally screwed in place in much the same manner as a
spark plug. There is a special socket wrench (cost is under $10.00) that can
accomodate the wire. The special wrench looks much the same as a spark plug
socket, but has a slot cut in the side for the wire. Simply disconnect the
wire at the connector, and unscrew the old sensor and put the new one in.
I get that you might not be much of a mechanic, but my point is to express
how basic and simple this job is. It's like taking a spark plug out and
putting in a new one. There can be issues of corrosion and heat damage that
can make the job a pain in the ass, but if it goes right, it's really very
A catyltic converter ("cat") cleans up the exhaust gases. If it is not
doing its job because the catalyst is contaminated or coated, the second or
"downstream" O2 sensor will detect this and the computer will turn on the
check engine light.
The Corolla has a 4 cylinder engine, with all 4 cylinders lined up in a row,
referred to as a "bank." This layout is known as an in-line engine. Other
engines have cylinders arranged in a "V" or "H" configuration. Think of a
V-6 or V-8 engine as two 3 or 4 cylinder in-line engines joined at the
bottom in a "V" shape. These engines have 2 rows, or banks of cylinders.
I was asked by an exhuast
Your car has two O2 sensors. Sensor #1 (sometimes referred to as the
"upstream" sensor) measures the oxygen in the exhaust as it exits the
engine. The car's electronic control unit ("ECU" or computer) adjusts the
amount of fuel injected into the engine based on what O2 sensor #1 sniffs in
After the exhaust gas passes through the cat, O2 sensor #2 (sometimes
referred to as the "downstream" sensor) takes another sniff and sends a
signal to the ECU. If the exhaust gas is not clean enough, the ECU assumes
that the cat is not working properly and turns on the check engine light.
It is possible that sensor #2 is not working properly and thinks it is
smelling too much pollutants in the exhaust.
One possibility is that whatever contaminated the catalyst could also
contaminate the O2 sensor, which is why you would need to replace both at
the same time.
Personally, I wouldn't bother with the O2 sensors unless you get another
check engine light after the cat is replaced and the ECU points to one or
both of the sensors.
If you can change the brakes on your own car, you can change the O2 sensors.
Sensor #1 is probably located in the exhaust manifold, visible when you open
the hood. It will be screwed into the manifold with a wire connector coming
out of it and is about the diameter of your finger. Sensor #2 looks just
like Sensor #1 and is located in the exhaust pipe after the cat.
correct the return address punctuation to reply
What if "sensor #2 is not working properly and thinks it is smelling
too much pollutants in the exhaust."? Is there a way to check #2 O2
sensor good or bad first before having CAT replaced? CAT replacement is
so expensive, I hope that I can identify the condition of #2 O2 sensor.
To check O2 sensor operation, you will need a volt/ohm meter or
Start the engine and let it warm up to operating temperature, turn
Run the engine to at least 2,500 RPM to heat up the O2 sensor.
You should get a reading that swings from less than 400 millivolts DC to
greater than 550 millivolts DC at least 8 times in 10 seconds. If the lower
voltage reading is above 400 mv or the higher voltage reading is not at
least 550 mv then the O2 sensor is bad. If it doesn't swing back and forth
8 times in 10 seconds then the O2 sensor is bad.
correct the return address punctuation to reply
This is a good procedure for the O2 sensor before the catalytic converter,
but won't work for the sensor after the catalytic converter, if the
converter is working. The output from the sensor after the converter varies
much less since, if the converter is working, there should be little or no
unburned hydrocarbons left.
You should know by now that the last couple of years, Toyota has NOT used a
conventional "O2" sensor before the catalyst. After the catalyst, same ol
O2 but the input is only used for catalyst performance tracking. The
current technology employs an exhaust sensor that operates on a different
principle and is called an Air/Fuel ratio sensor. They are NOT
That is most likely what is going on. The sensor is failing -- or has
failed -- and is sending a false report. There's a chance that the CAT is
toast, but if I was doing the job on my own car, I'd replace the sensor
before I did anything.
I'd actually reset the Check light, then wait to see if it comes on again.
If it does, AND it has the same code P0420, then I'd replace the sensor,
reset the code, and wait again.
Your car is compliant to On Board Diagnostics, Level 2 (OBD II), and you can
do a search on the Web to learn more.
AutoZone (an auto parts store) will let you use the coed reader for free.
The reader will reset the codes. There are readers on eBay that cost in the
range of about $60 to about $150. There are four models from the same maker
that have varying features and abilities, my suggestion is that the tool
costing in the mid range is the one tha tmost of us ShadeTree mechanics will
need. If you have an AutoZone store nearby, and don't want to buy another
tool that won't get much use, then go to the corner and use theirs for free.
When you search the 'net for "OBD II" yo will find more than you ever wanted
to know. Do the same search on eBay, and you'll uncover lots of sources for
the tool. AutoZone has them for sale, or you can use theirs for free. If you
want to use it in the parking lot, then you just leave your driver license
as a security device. If you want to take the tool home, then they will ring
it up on a credit card, then give a Full Refund when you bring the tool
back. I've used the tool both ways, in the parking lot and at home.
I'm in California, and they are expressly prohibited from checking my car
for me, but they can let me use the tool to check it myself. If they will
check the car for you, then even better because this takes away at least one
level of difficulty.
Your car does have two O2 sensors, one in front of the catalytic converter,
close to the engine (possibly in the exhaust manifold, or just after), and
one after the catalytic converter. The one before the converter is used by
the engine computer to adjust the fuel mixture. The one after the catalytic
converter is used to make sure the converter is working.
Personally, I'd try replacing the O2 sensor after the converter before I
bought a catalytic converter. You really should not need both. If the
converter failed, the O2 sensor after the converter is probably OK, since it
warned you that the converter had failed. If the converter is still OK, then
the sensor after the converter must be bad since it identified the converter
as bad when it wasn't. No reason for both to fail at the same time.
You said you recently passed your states inspection. Did they actually
measure exhaust emission during their test? If so and you passed, I'd be
inclined to think the catalytic converter was OK.
If I replace #2 O2 sensor before replacing CAT, is it possible that the
new O2 sensor get damaged by sniffing too much the "dirty stuff"
because of a bad CAT?
Believe or not, the exact same dealer did the state inspection on the
exact the same car, it passed PA inspection.
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