Question about 2004 Toyota Corolla

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Check Engine Light was on for Downstream O2 sensor, I decided to clean the fuel injectors because i haven't done that in 30,000 miles. Check engine light goes off. Is it possible that the CEL for the O2 sensor was on because an injector was stuck on or stuck closed, even though no injectors appeared to be damages, or stuck open/close?

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Downstream O2 is after the cat. A severe rich mix could set code. If one of the injectors was leaking due to dirt , it should have caused a miss in that cylinder. I hope that cleaning has solved your problem.

Posted on Jul 18, 2009


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Engine Code O2 Sensor Circuit, HV Bank 1, Sensor 2

You did not say what your car was ,however most newer cars use 2 oxygen sensors per bank, if it is a 4 cyl replace downstream o2 sensor,if 6 or 8 cyl bank 1 sensor 2 is downstream sensor on bank that has cyl 1 on it.upstream sensor is in front of catalytic converter downstream is after the cat

Mar 17, 2015 | Cars & Trucks

2 Answers

I have a 2010 Buick Lacrosse that had the P0420 code. Replaced the Bank One Cat and the code and the check engine light came on again with the same code.

Did they use an original equipment cat from the dealer or an aftermarket one? Aftermarket cats can cause more problems than they fix. There very few that I will personally install.

are they monitoring downstream O2 sensor data to see if the O2 sensor may be biased high? If the cat is doing its job the downstream O2 sensors will read a lower voltage. Tricking the vehicle into running rich or lean will cause this voltage to change ( unplugging a coil will cause the Downstream O2 to read high as the cat tries to burn off the extra fuel. Unplugging a fuel injector will cause the downstream O2 sensor to read low as extra air is being pushed thought the cats). Making sure the downstream O2 sensors are capable of switching should be part of the diagnostics.

Are you sure they replace the right cat? There are 5 different engine options for this car. If you let me know what engine you have I can let you know what bank is bank 1.

Feb 20, 2015 | 2010 Buick LaCrosse CXL

2 Answers


Mine had the same problem at 30,000 miles, it was in fact the O2 sensor. I had it replaced and haven't had the CEL since. I've noticed that RSX's have this problem quite often, so don't be too surprised.
Let me know if this helps.

May 10, 2011 | 2006 Acura RSX

1 Answer

I have a 2006 Freestar with a 3.9 Engine . When it is cold it has a miss when i step on it. But it gets better when it starts to warm up. Almost seems like a spark plug miss

Spark Plugs ---change at 70,000 miles
O2 Sensors--change at 100,000 miles (front 2 only)
Gas Filter--every 3 years/30,000 miles
Air Filter ---every 3 years/blow off once every year
MAF Sensor---Clean once a year or more often

Ignition Coils--- most definitely will go bad,at
least 1 a year. (Any Check Lights or Codes ? )

When cold, it isn't in closed-loop, and runs on
Long Term Fuel Trim--not on O2 Sensors ,until

Let it warm up at least 4 minutes in cold weather,
go light on the gas for first 2 miles

Feb 22, 2011 | 2006 Ford Freestar

1 Answer

My 1999 honda odyssey have a light on in the check engine, i went to the mechanic & plug it to the small computer, the computer said no response to code P0138B BANK 1 SENSOR 2 HIGHT VOLT, the mechanic...

There is are upstream and downstream O2 sensors. 1 or 2 (upstream) before the catalytic converter which sends signals for closed loop fuel control and OBD II monitoring, and 1 (downstream) after the catalytic converter, which is used to monitor the catalytic converter operation. The PCM monitors the signal from each O2 sensor.

Nov 02, 2010 | 2006 Honda Odyssey

2 Answers

Have a 1999 Chevy Tahoe, It is throwing 3 codes....PO172, PO420 and PO300 what can cause theese?

* p0172 bank 1 rich. If you have access to a scan tool, I would check the fuel trim and see if engine is running rich all the time. In Chevy, if both banks are too lean or too rich, usually the cause is the Mass Air Flow sensor being dirty.
* P0420 The PCM copares switch rates between the front O2 sensors and the downstream catalyst moniters. The catylist moniters are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called. By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust. If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, and sets a P0420, bank 1 it is. To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely. If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you proabably need a catalytic converter. Most likely related to the P0172 code above.
* P0300 multi misfire probable cause. Fuel injectors always seem to get the blame for this one since the there is only a lean condition to one side of the engine.
The fuel injectors on these trucks really have one problem, the poppet nozzles at the end. They can stick either open or closed. If they are stuck closed, then servicing the system will clear up the problem (I recommend that they use the 'top engine cleaner' over anything else). However, if they are stuck OPEN, then no amount of cleaning or servicing will fix the problem unless the nozzles are replaced.
Here is a TSB link to the GM's upgrade from the SCPI to MPI system for your truck.
Here is also a link to the conversion being done on a 4.3 V6 vortec with the same issues your having.
Good luck and try using fuel injector cleaner first to address the issue, Lucas fuel injector cleaner is great for the price for how much you get for it. Just follow the instructions on the bottle and you should be good for a month of injector cleaner when you fill up the gas tank.
Thank you for using Fixya

Mar 16, 2010 | 1999 Chevrolet Tahoe

2 Answers

When should the transmission fluid be flushed? When should the Fuel injection be serviced?

every 30,000 on the transmisson and use lucas fuel stablizer cleaner ot work on the injectors and do a top engine clean after 100,000 to prevent engine detonation (Knock).

Sep 28, 2009 | 2001 Ford Focus

1 Answer

Engine has miss-fire

First check spark plugs/wires/distributor cap (tune up). Also would be good idea to use fuel injector cleane and change fuel filter and O2 sensor.
Hope that helps
Good Luck

Mar 22, 2009 | 2003 Audi TT

1 Answer

Engine code on a neon

it sounds like you have a fuel issue. you should check for proper fuel pressure. its should be 48 PSI.

if its not, it could be a clogged fuel filter, a malfunctioning fuel pressure regulator, clogged fuel pump strainer, or even a bent, kinked fuel line.

if the fuel pressure is correct, its most likely a faulty fuel injector.

by the way, you car doesn't have a mass airflow sensor, it has a MAP sensor

Oct 22, 2008 | 1996 Plymouth Neon

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