Question about 2001 Toyota Sienna

1 Answer

Engine code P0420

If I order a replacment part and install it myself. Does the new ECM need to be flashed??

Posted by on


1 Answer

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 20 achievements.


    An expert that got 10 achievements.


    An expert that got 5 achievements.

  • Toyota Master
  • 20,706 Answers

What a great loaded question, 3L V6 and Camry based car.

CE, LE, or XLE?

in USA?

what new PCM.? what parts changed, list all parts.

the FSM covers this. read it. (extensive it is)

you said new ECM(pcm), well is that from Toyota? or whom.?????

i sure cant guess your PCM source, there are many.

used, new TOY,rebuilt and aftermarket new.

the factory PCM on most cars are slicked, and must be flashed

to your options. and model, in fact this is a top goal of all car makers

1 ECU and fits 100 cars. a dream that is working.....

on a 2001 , well let see.

on line

Federal car or Calif car. 2 ECMs. in usa. (it dont mention flashing)

ouch $700 part.

are you sure its bad, most are, did you know about 85% sent in

are good
, owners out $700 .?

got the IMMO option, if yes, it will never run.

immoblizer. RTM read the FSM manual;. its all there.

point 2, and best of all ,why not join a real forum

and get help from folks that deal with all this.

The IMMO rules on most toyotas are the strictist of all cars.

never ever lose the master key or use it for daily use.

now back to the Blue box. P0420

the ECM is not bad for this..

it means the CAT is weak. (or dead)

THE PCM monitors the CAT with a rear 02 sensor

this sensor loose like line, drawn by a drunk man. tiny jiggles

about 0.5v.

if the cat is bad this sensor B1S2 or B2S2, (do you have 2 sensor 2\'s)

if this O2 jumps widely, this means the cat is bad, its not working


HUGE NASTY SMOG exiting the engine, Engine runs like crap

we fix the engine first. then drive 100mile, in closed loop and bake t

the old cat dry. reset the PCM and see of 420s stop

if not, a new 02 , and or cat.

that is how 420s work. fix 420s DEAD LAST , always.

in shops the just slam in parts, labor is too expensive

but a DIY guy can fix the engine then bake the cat.

it does work , done it many a time.

even with cat full of oil, from a blown engine.

smoked white 20 miles ,then woke up and passed all smog.

tell more, get more.

Posted on Jan 03, 2014


1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of.(from cars to computers, handyman, and even drones)
click here to download the app (for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

2 Answers

What does trouble code p0420

p420 code has to do with your exhaust system,catylic converters,..sensors...could be a simple fix or not...

Sep 19, 2014 | 2003 Chrysler Town & Country

1 Answer

P0420 code


Apr 29, 2014 | 2005 Hyundai Elantra

1 Answer

P0420 code evap system

This is not an evap code. Read on:
P0420 - Catalyst System Efficiency Below Threshold Bank 1

Possible causes- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM)
Tech notes The most common cause it the three way catalyst converter Bank 1. Changing just the O2 sensor usually don't repair the problem. If the P0420 code is combined with other codes, try fixing the other codes first.

Nov 02, 2012 | Cars & Trucks

1 Answer

I have 1999 gmc new Sierra Z71 1500 4wd 4.8 8cil shows code P0420 what can I do to fixed

P0420 - Catalyst System Efficiency Below Threshold (it not cleaning the exhaust up)
Possible causes- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM)

Oct 11, 2012 | Cars & Trucks

2 Answers

How do I correct my 2000 Toyota Camry CE P0420 code?

Replace the catalytic converter with a factory replacement. Do not use an aftermarket generic replacement.

May 22, 2012 | Cars & Trucks

1 Answer

1998 buick century code p0420

code p 0420 refers to cat converter system bank 1---efficiency below threshold====causes ---cat converter---wiring---HO2S (heated oxygen sensor, the one in the exhaust manifold before the cat converter)
code p 0300 is random misfires
I would suggest changing the HO2S as it reports to the ECM on exhaust content so that the ECM can adjust the air/fuel ratio
so it is logical that if that unit is not reporting correctly, the cat converter may be having trouble burning off the gasses correctly
The oxygen sensor(O2S) reads the results of the cat converter operation and helps fine tune the ECM settings

Mar 10, 2017 | 1998 Buick Century

1 Answer


P0420, this code comes ON when the O2 sensors reading go out of the range set by the factory. In some other models, the factory increased the range of the O2 sensor with a new program for the Engine Control Module (ECM), because the O2 sensors are still consider to be in normal operation. If the code comes back, I recommend reprogramming the ECM first. dealer has to program ecm try changeing your cars thermostat it also may shut off light before going to dealer

Dec 22, 2010 | Toyota Corolla Cars & Trucks

1 Answer

I have a 2001 chevy S-10 2.2 liter. What does Code P0420 mean??

here are a number of things that could be causing this p0420 catalyst efficiency code. The most common thing is the catalytic converter itself is no longer functioning properly.
The other likely thing is the rear O2 (oxygen) sensor is no longer working properly. Other things could include exhaust leaks, damaged exhaust pipes, damaged O2 sensor wiring/connectors, plugged catalytic converter, etc.
The easiest thing to do first is a visual check of things. Visually inspect the exhaust system for leaks, check the catalytic converter for dents, holes, severe discoloration, and check for a rattle inside. If any of those syptoms are there, the converter likely needs replacement.
Then, visually inspect the downstream O2 sensor (behind the converter). Check for broken wires, obvious faults, etc. If all that checks out, you'll want to check the operation of the O2 sensor. To do that, you'll need access to a scan tool or oscilliscope. Check that the waveform is pretty steady. If the reading fluctuates then the sensor is likely bad and will need to be replaced.
Try this, turn the ignition key to the on position, (engine not running) and pull the fuse to your ECM for 30 seconds and then re-install it. Once re-installed, start the engine and let idle for 1 min and then go for a test drive.
If the engine stalls, let it. The ECM is relearning the sensors and engine, just restart it and after 1 min when the RPM drops. God for a test drive and see if the service engine light comes back on and re-scan for the DTC codes and address the issues indicated by the DTC code.
Thank you for using fixya and good luck.

Apr 18, 2010 | 2003 Chevrolet S-10

3 Answers

I had my car inspected and received P0420 code? what does it mean?

P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1) Repair information for the OBD-II trouble code P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

Feb 18, 2010 | 2000 Toyota Celica

2 Answers

Trouble shooting P0420 code, bank 1, OBD II for 2000'?

misfiring can cause a P0420 code.
I would recommend a set of honda plug wires and plugs if the P0420 code returns.
I have used bolt in aftermarket bolt in catalytic converters but don't remember the brand name they fit ok and i have had 1 or 2 return with a P0420 code out of about 20. I have never replaced the oxygen sensor on a civic like yours.
I always fix the misfire problems, reset the computer, and have the customer drive it and see if the code p0420 returns. 50% don't have the P420 code return. drive it and see what happens and go from there.

Jan 06, 2009 | 2000 Honda Civic

Not finding what you are looking for?
2001 Toyota Sienna Logo

331 people viewed this question

Ask a Question

Usually answered in minutes!

Top Toyota Experts


Level 3 Expert

76846 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22246 Answers

Jeffrey Turcotte
Jeffrey Turcotte

Level 3 Expert

8547 Answers

Are you a Toyota Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides