Skip the auto shop - Our mechanics make house calls

Q: p0420

asked by on

i have a p420 , i know that the p420 has to do with the catalytic converter..but by replacing the catalytic converter will erase code p420 or there are other problems that might be causing a p420, i use to have a p133 and p420..but when the ozone sensor was replaced i dont get that anymore..just the p420..i just want to make sure its a new catalytic converter i need b4 i have it replaced..thanks

My car has 182000 miles.
My car has an automatic transmission.

A: A vehicle with 182,000 miles is likely due ...

A vehicle with 182,000 miles is likely due for a catalytic converter. Most of the time it does mean you need a new catalytic converter. But there are a couple of other things that are prudent to take a look at. Number one, using a shop level scanner, look at the downstream O2 sensor operation. With the car running, you need to snap the throttle. In other words, quickly floor it and let off. This will inject as much fuel into the motor as possible. The O2 sensor should register this change, but not excessively. The upstream O2 oscillates between one volt and zero volts quickly, if the downstream O2 is doing the same, the catalytic converter is not doing anything. To summarize, the downstream O2 should react to a snapped throttle, but it should not spike like the upstream O2 does.

The other possibility is the PCM may need to be flashed. This will change the programming to adapt to the condition of an older vehicle. Before this is considered, you will want to perform the first procedure I outlined first. Of Course, this requires a shop level scanner, and ideally a five gas analyzer to monitor what is coming out the tail pipe. If the downstream O2 and the tail pipe emissions are within specifications, then it is time to consider flashing the PCM.

Flashing the PCM should only be done by an experienced technician. There is potential to leave your PCM dead. So it is not something even an seasoned technician should attempt without guidance from someone who has done it before. In addition, you will want to check with Toyota to see if there is a PCM update available that makes the appropriate changes addressing catalytic converter operation.

I recommend contacting customer service to see if there is a technician in your area with the experience necessary to take on this project.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: What does the trip information display do?

Your car is equipped with a screen that displays a wide range of different information pertinent to your trip called the trip information display. The information here ranges from the outside temperature to the average fuel mileage and more. To...

Q: Idles great, but won't accelerate

This may be caused by any number of things, but may be most commonly associated with a clogged catalytic converter. As you may already know, the catalytic converter converts toxic exhaust gases into less harmful pollutants that are suitable to...

Q: Code P0420 shows on the dash of my 2005 Acura MDX

Acura did have a tech bulletin released in September 2011 regarding fault P0420 and a possible software update that may rectify this situation. You can try contacting your local Acura dealer service department or Acura Customer service to see if...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.