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Where is the O2sensor bank 1 at with a code of P0420. AND do I need to replace both sensors upstream and down. Or just the one that is showing up on the obd scanner.

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P0420 means that the computer has determined that the catalytic converter is performing below threshhold of efficiency. The computer determines this by comparing the signals of the upstream O2 sensor with the downstream O2 sensor.
The oxygen content at the upstream sensor varies up and down as the computer makes constant small adjustments to the air/fuel ratio for the engine. The oxygen content at the downstream sensor should show a consistently low level of oxygen it the catalytic converter is working efficiently. When the signal from the downstream sensor 'mimics' the upstream sensor, this triggers the P0420 code.
So replacing the sensors is not going to resolve the issue. They are both working or the computer could not determine that the catalyic converter is working below its target efficiency.
Make sure the engine is tuned properly, that you don't have any leaking injectors, have the light reset, and drive normally. If the light comes on again, you probably need a new catalytic converter.

Posted on Jan 02, 2017

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Bank one is front side of cat. It should also tell u if it's cat 1 or cat 2. Depending on make an modle an yr. Catalyst 1 bank 2 is left cat back sensor. Catalyst 2 bank 2 is right cat back sensor. U do not have to replace upstream also. My o2 sensor Catalyst 2 bank 2 went bad. Had engine code for burning rich bank 2. Replaced tha down stream sensor an fixed problem runs better an better gas. This was in 97 gmc suburban. Idk what vehicle ur askin about. An I'm not to familiar with much about cars jus trucks an suvs.

Posted on Jan 02, 2017

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Posted on Jan 02, 2017

vitaforall
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SOURCE: 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.

Posted on Jan 06, 2009

  • 87 Answers

SOURCE: I have a P0420 code catalyst efficiency below

it is a bad converter not o 2 sensor i would change the cat and both o 2 sensors

Posted on Mar 09, 2009

pdbaker6
  • 70 Answers

SOURCE: obd code P0135 on a lexus ls400

usually your first sensor is located on the exhaust manifold

Posted on Jun 22, 2009

  • 753 Answers

SOURCE: 3 codes present on my 2002 Envoy. p0172, p0420, and p0340,

Track the p0340 first camshaft timing is very important and could possibly cayse your other codes,Call your local GMC dealer I think I remember a bulletin about this code.

Posted on Aug 23, 2009

SOURCE: Getting PO141 trouble code when scanning! Car '03 accord, 2.4 ltr

i spoke to a honda tech , and he confirmed code p0141 on the 4cylinder model is the second sensor.

Posted on Aug 28, 2009

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Should i replace the oxygen sensor bank 1? Is it downstream or upstream?codep0420 2006 quest


you need to test both can be either one or it can be a different sensor the following link can assist in breaking down what sensors to check
http://www.obd-codes.com/p0420

Jul 14, 2016 | Cars & Trucks

2 Answers

What means catalyst Efficiency below normal


      Got it scanned and it's P0420: Catalyst efficiency below thresholdbank 1. They said it could be a bad catalytic converter or oxygen sensor. I borrowed a scanner and tried to measure the oxygen sensor readings over time.Sep 8, 2011

      civic - Check Engine code P0420 Catalyst efficiency below ...

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    www.obd-codes.com/p0420
    P0420 OBD-II Trouble Code. Technical Description. Catalyst System Efficiency Below Threshold (Bank 1). What does that mean? This diagnostic trouble code ...

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1 Answer

Where is the bank 1 sensor 1 air flow sensor located on a 2000 toyota avalon?


Sensor diagram for a 2000 toyota avalon and list of Pcodes dbd372cc-f8f3-49ef-b0c2-2adab46c4182.jpg 8fc069a5-bedc-447d-a1ef-4335798a0a0f.jpg

P0100 Mass or Volume Air Flow Circuit Malfunction
P0101 Mass or Volume Air Flow Circuit Range/Performance Problem
P0102 Mass or Volume Air Flow Circuit Low Input
P0103 Mass or Volume Air Flow Circuit High Input
P0104 Mass or Volume Air Flow Circuit Intermittent
P0105 Manifold Absolute Pressure/Barometric Pressure Circuit Malfunction
P0106 Manifold Absolute Pressure/Barometric Pressure Circuit Range/Performance Problem
P0107 Manifold Absolute Pressure/Barometric Pressure Circuit Low Input
P0108 Manifold Absolute Pressure/Barometric Pressure Circuit High Input
P0109 Manifold Absolute Pressure/Barometric Pressure Circuit Intermittent
P0110 Intake Air Temperature Circuit Malfunction
P0111 Intake Air Temperature Circuit Range/Performance Problem
P0112 Intake Air Temperature Circuit Low Input
P0113 Intake Air Temperature Circuit High Input
P0114 Intake Air Temperature Circuit Intermittent
P0115 Engine Coolant Temperature Circuit Malfunction
P0116 Engine Coolant Temperature Circuit Range/Performance Problem
P0117 Engine Coolant Temperature Circuit Low Input
P0118 Engine Coolant Temperature Circuit High Input
P0119 Engine Coolant Temperature Circuit Intermittent
P0120 Throttle/Pedal Position Sensor/Switch "A" Circuit Malfunction
P0121 Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance Problem
P0122 Throttle/Pedal Position Sensor/Switch "A" Circuit Low Input
P0123 Throttle/Pedal Position Sensor/Switch "A" Circuit High Input
P0124 Throttle/Pedal Position Sensor/Switch "A" Circuit Intermittent
P0125 Insufficient Coolant Temperature For Closed Loop Fuel Control
P0126 Insufficient Coolant Temperature For Stable Operation
P0130 O2Circuit Malfunction (Bank #1 Sensor #1)
P0131 O2Sensor Circuit Low Voltage (Bank #1 Sensor #1)
P0132 O2Sensor Circuit High Voltage (Bank #1 Sensor #1)
P0133 O2Sensor Circuit Slow Response (Bank #1 Sensor #1)
P0134 O2Sensor Circuit No Activity Detected (Bank #1 Sensor #1)
P0135 O2Sensor Heater Circuit Malfunction (Bank #1 Sensor #1)
P0136 O2Sensor Circuit Malfunction (Bank #1 Sensor #2)
P0137 O2Sensor Circuit Low Voltage (Bank #1 Sensor #2)
P0138 O2Sensor Circuit High Voltage (Bank #1 Sensor #2)
P0139 O2Sensor Circuit Slow Response (Bank #1 Sensor #2)
P0140 O2Sensor Circuit No Activity Detected (Bank #1 Sensor #2)
P0141 O2Sensor Heater Circuit Malfunction (Bank #1 Sensor #2)
P0142 O2Sensor Circuit Malfunction (Bank #1 Sensor #3)
P0143 O2Sensor Circuit Low Voltage (Bank #1 Sensor #3)
P0144 O2Sensor Circuit High Voltage (Bank #1 Sensor #3)
P0145 O2Sensor Circuit Slow Response (Bank #1 Sensor #3)
P0146 O2Sensor Circuit No Activity Detected (Bank #1 Sensor #3)
P0147 O2Sensor Heater Circuit Malfunction (Bank #1 Sensor #3)
P0150 O2Sensor Circuit Malfunction (Bank #2 Sensor #1)
P0151 O2Sensor Circuit Low Voltage (Bank #2 Sensor #1)
P0152 O2Sensor Circuit High Voltage (Bank #2 Sensor #1)
P0153 O2Sensor Circuit Slow Response (Bank #2 Sensor #1)
P0154 O2Sensor Circuit No Activity Detected (Bank #2 Sensor #1)
P0155 O2Sensor Heater Circuit Malfunction (Bank #2 Sensor #1)
P0156 O2Sensor Circuit Malfunction (Bank #2 Sensor #2)
P0157 O2Sensor Circuit Low Voltage (Bank #2 Sensor #2)
P0158 O2Sensor Circuit High Voltage (Bank #2 Sensor #2)
P0159 O2Sensor Circuit Slow Response (Bank #2 Sensor #2)
P0160 O2Sensor Circuit No Activity Detected (Bank #2 Sensor #2)
P0161 O2Sensor Heater Circuit Malfunction (Bank #2 Sensor #2)
P0162 O2Sensor Circuit Malfunction (Bank #2 Sensor #3)
P0163 O2Sensor Circuit Low Voltage (Bank #2 Sensor #3)
P0164 O2Sensor Circuit High Voltage (Bank #2 Sensor #3)
P0165 O2Sensor Circuit Slow Response (Bank #2 Sensor #3)
P0166 O2Sensor Circuit No Activity Detected (Bank #2 Sensor #3)
P0167 O2Sensor Heater Circuit Malfunction (Bank #2 Sensor #3)
P0170 Fuel Trim Malfunction (Bank #1)
P0171 System Too Lean (Bank #1)
P0172 System Too Rich (Bank #1)
P0173 Fuel Trim Malfunction (Bank #2)
P0174 System Too Lean (Bank #2)
P0175 System Too Rich (Bank #2)
P0176 Fuel Composition Sensor Circuit Malfunction
P0177 Fuel Composition Sensor Circuit Range/Performance
P0178 Fuel Composition Sensor Circuit Low Input
P0179 Fuel Composition Sensor Circuit High Input
P0180 Fuel Temperature Sensor "A" Circuit Malfunction
P0181 Fuel Temperature Sensor "A" Circuit Range/Performance
P0182 Fuel Temperature Sensor "A" Circuit Low Input
P0183 Fuel Temperature Sensor "A" Circuit High Input
P0184 Fuel Temperature Sensor "A" Circuit Intermittent
P0185 Fuel Temperature Sensor "B" Circuit Malfunction
P0186 Fuel Temperature Sensor "B" Circuit Range/Performance
P0187 Fuel Temperature Sensor "B" Circuit Low Input
P0188 Fuel Temperature Sensor "B" Circuit High Input
P0189 Fuel Temperature Sensor "B" Circuit Intermittent
P0190 Fuel Rail Pressure Sensor Circuit Malfunction
P0191 Fuel Rail Pressure Sensor Circuit Range/Performance
P0192 Fuel Rail Pressure Sensor Circuit Low Input
P0193 Fuel Rail Pressure Sensor Circuit High Input
P0194 Fuel Rail Pressure Sensor Circuit Intermittent
P0195 Engine Oil Temperature Sensor Malfunction
P0196 Engine Oil Temperature Sensor Range/Performance
P0197 Engine Oil Temperature Sensor Low
P0198 Engine Oil Temperature Sensor High
P0199 Engine Oil Temperature Sensor Intermittent
P0200 Injector Circuit Malfunction
P0201 Injector Circuit Malfunction - Cylinder #1
P0202 Injector Circuit Malfunction - Cylinder #2
P0203 Injector Circuit Malfunction - Cylinder #3
P0204 Injector Circuit Malfunction - Cylinder #4
P0205 Injector Circuit Malfunction - Cylinder #5
P0206 Injector Circuit Malfunction - Cylinder #6
P0207 Injector Circuit Malfunction - Cylinder #7
P0208 Injector Circuit Malfunction - Cylinder #8
P0209 Injector Circuit Malfunction - Cylinder #9
P0210 Injector Circuit Malfunction - Cylinder #10
P0211 Injector Circuit Malfunction - Cylinder #11
P0212 Injector Circuit Malfunction - Cylinder #12
P0213 Cold Start Injector #1 Malfunction
P0214 Cold Start Injector #2 Malfunction
P0215 Engine Shutoff Solenoid Malfunction
P0216 Injection Timing Control Circuit Malfunction
P0217 Engine Over Temperature Condition
P0218 Transmission Over Temperature Condition
P0219 Engine Over Speed Condition
P0220 Throttle/Pedal Position Sensor/Switch "B" Circuit Malfunction
P0221 Throttle/Pedal Position Sensor/Switch "B" Circuit Range/Performance Problem
P0222 Throttle/Pedal Position Sensor/Switch "B" Circuit Low Input
P0223 Throttle/Pedal Position Sensor/Switch "B" Circuit High Input
P0224 Throttle/Pedal Position Sensor/Switch "B" Circuit Intermittent
P0225 Throttle/Pedal Position Sensor/Switch "C" Circuit Malfunction
P0226 Throttle/Pedal Position Sensor/Switch "C" Circuit Range/Performance Problem
P0227 Throttle/Pedal Position Sensor/Switch "C" Circuit Low Input
P0228 Throttle/Pedal Position Sensor/Switch "C" Circuit High Input
P0229 Throttle/Pedal Position Sensor/Switch "C" Circuit Intermittent
P0230 Fuel Pump Primary Circuit Malfunction
P0231 Fuel Pump Secondary Circuit Low
P0232 Fuel Pump Secondary Circuit High
P0233 Fuel Pump Secondary Circuit Intermittent
P0234 Engine Over Boost Condition
P0261 Cylinder #1 Injector Circuit Low
P0262 Cylinder #1 Injector Circuit High
P0263 Cylinder #1 Contribution/Balance Fault
P0264 Cylinder #2 Injector Circuit Low
P0265 Cylinder #2 Injector Circuit High
P0266 Cylinder #2 Contribution/Balance Fault
P0267 Cylinder #3 Injector Circuit Low
P0268 Cylinder #3 Injector Circuit High
P0269 Cylinder #3 Contribution/Balance Fault
P0270 Cylinder #4 Injector Circuit Low
P0271 Cylinder #4 Injector Circuit High
P0272 Cylinder #4 Contribution/Balance Fault
P0273 Cylinder #5 Injector Circuit Low
P0274 Cylinder #5 Injector Circuit High
P0275 Cylinder #5 Contribution/Balance Fault
P0276 Cylinder #6 Injector Circuit Low
P0277 Cylinder #6 Injector Circuit High
P0278 Cylinder #6 Contribution/Balance Fault
P0279 Cylinder #7 Injector Circuit Low
P0280 Cylinder #7 Injector Circuit High
P0281 Cylinder #7 Contribution/Balance Fault
P0282 Cylinder #8 Injector Circuit Low
P0283 Cylinder #8 Injector Circuit High
P0284 Cylinder #8 Contribution/Balance Fault
P0285 Cylinder #9 Injector Circuit Low
P0286 Cylinder #9 Injector Circuit High
P0287 Cylinder #9 Contribution/Balance Fault
P0288 Cylinder #10 Injector Circuit Low
P0289 Cylinder #10 Injector Circuit High
P0290 Cylinder #10 Contribution/Balance Fault
P0291 Cylinder #11 Injector Circuit Low
P0292 Cylinder #11 Injector Circuit High
P0293 Cylinder #11 Contribution/Balance Fault
P0294 Cylinder #12 Injector Circuit Low
P0295 Cylinder #12 Injector Circuit High
P0296 Cylinder #12 Contribution/Balance Fault
P0300 Random/Multiple Cylinder Misfire Detected
P0301 Cylinder #1 - Misfire Detected
P0302 Cylinder #2 - Misfire Detected
P0303 Cylinder #3 - Misfire Detected
P0304 Cylinder #4 - Misfire Detected
P0305 Cylinder #5 - Misfire Detected
P0306 Cylinder #6 - Misfire Detected
P0307 Cylinder #7 - Misfire Detected
P0308 Cylinder #8 - Misfire Detected
P0320 Ignition/Distributor Engine Speed Input Circuit Malfunction
P0321 Ignition/Distributor Engine Speed Input Circuit Range/Performance
P0322 Ignition/Distributor Engine Speed Input Circuit No Signal
P0323 Ignition/Distributor Engine Speed Input Circuit Intermittent
P0325 Knock Sensor #1 - Circuit Malfunction (Bank #1 or Single Sensor)
P0326 nock Sensor #1 - Circuit Range/Performance (Bank #1 or Single Sensor)
P0327 Knock Sensor #1 - Circuit Low Input (Bank #1 or Single Sensor)
P0328 Knock Sensor #1 - Circuit High Input (Bank #1 or Single Sensor)
P0329 Knock Sensor #1 - Circuit Input Intermittent (Bank #1 or Single Sensor)
P0330 Knock Sensor #2 - Circuit Malfunction (Bank #2)
P0331 Knock Sensor #2 - Circuit Range/Performance (Bank #2)
P0332 Knock Sensor #2 - Circuit Low Input (Bank #2)
P0333 Knock Sensor #2 - Circuit High Input (Bank #2)
P0334 Knock Sensor #2 - Circuit Input Intermittent (Bank #2)
P0335 Crankshaft Position Sensor "A" Circuit Malfunction
P0336 Crankshaft Position Sensor "A" Circuit Range/Performance
P0337 Crankshaft Position Sensor "A" Circuit Low Input
P0338 Crankshaft Position Sensor "A" Circuit High Input
P0339 Crankshaft Position Sensor "A" Circuit Intermittent
P0340 Camshaft Position Sensor Circuit Malfunction
P0341 Camshaft Position Sensor Circuit Range/Performance
P0342 Camshaft Position Sensor Circuit Low Input
P0343 Camshaft Position Sensor Circuit High Input
P0344 Camshaft Position Sensor Circuit Intermittent
P0350 Ignition Coil Primary/Secondary Circuit Malfunction
P0351 Ignition Coil "A" Primary/Secondary Circuit Malfunction
P0352 Ignition Coil "B" Primary/Secondary Circuit Malfunction
P0353 Ignition Coil "C" Primary/Secondary Circuit Malfunction
P0354 Ignition Coil "D" Primary/Secondary Circuit Malfunction
P0355 Ignition Coil "E" Primary/Secondary Circuit Malfunction
P0356 Ignition Coil "F" Primary/Secondary Circuit Malfunction
P0357 Ignition Coil "G" Primary/Secondary Circuit Malfunction
P0358 Ignition Coil "H" Primary/Secondary Circuit Malfunction
P0359 Ignition Coil "I" Primary/Secondary Circuit Malfunction
P0360 Ignition Coil "J" Primary/Secondary Circuit Malfunction
P0361 Ignition Coil "K" Primary/Secondary Circuit Malfunction
P0362 Ignition Coil "L" Primary/Secondary Circuit Malfunction
P0370 Timing Reference High Resolution Signal "A" Malfunction
P0371 Timing Reference High Resolution Signal "A" Too Many Pulses
P0372 Timing Reference High Resolution Signal "A" Too Few Pulses
P0373 Timing Reference High Resolution Signal "A" Intermittent/Erratic Pulses
P0374 Timing Reference High Resolution Signal "A" No Pulses
P0375 Timing Reference High Resolution Signal "B" Malfunction
P0376 Timing Reference High Resolution Signal "B" Too Many Pulses
P0377 Timing Reference High Resolution Signal "B" Too Few Pulses
P0378 Timing Reference High Resolution Signal "B" Intermittent/Erratic Pulses
P0379 Timing Reference High Resolution Signal "B" No Pulses
P0380 Glow Plug/Heater Circuit "A" Malfunction
P0381 Glow Plug/Heater Indicator Circuit Malfunction
P0382 Glow Plug/Heater Circuit "B" Malfunction
P0385 Crankshaft Position Sensor "B" Circuit Malfunction
P0386 Crankshaft Position Sensor "B" Circuit Range/Performance
P0387 Crankshaft Position Sensor "B" Circuit Low Input
P0388 Crankshaft Position Sensor "B" Circuit High Input
P0389 Crankshaft Position Sensor "B" Circuit Intermittent
P0400 Exhaust Gas Recirculation Flow Malfunction
P0401 Exhaust Gas Recirculation Flow Insufficient Detected
P0402 Exhaust Gas Recirculation Flow Excessive Detected
P0403 Exhaust Gas Recirculation Circuit Malfunction
P0404 Exhaust Gas Recirculation Circuit Range/Performance
P0405 Exhaust Gas Recirculation Sensor "A" Circuit Low
P0406 Exhaust Gas Recirculation Sensor "A" Circuit High
P0407 Exhaust Gas Recirculation Sensor "B" Circuit Low
P0408 Exhaust Gas Recirculation Sensor "B" Circuit High
P0410 Secondary Air Injection System Malfunction
P0411 Secondary Air Injection System Incorrect Flow Detected
P0412 Secondary Air Injection System Switching Valve "A" Circuit Malfunction
P0413 Secondary Air Injection System Switching Valve "A" Circuit Open
P0414 Secondary Air Injection System Switching Valve "A" Circuit Shorted
P0415 Secondary Air Injection System Switching Valve "B" Circuit Malfunction
P0416 Secondary Air Injection System Switching Valve "B" Circuit Open
P0417 Secondary Air Injection System Switching Valve "B" Circuit Shorted
P0418 Secondary Air Injection System Relay "A" Circuit Malfunction
P0419 Secondary Air Injection System Relay "B" Circuit Malfunction
P0420 Catalyst System Efficiency Below Threshold (Bank #1)
P0421 Warm Up Catalyst Efficiency Below Threshold (Bank #1)
P0422 Main Catalyst Efficiency Below Threshold (Bank #1)
P0423 Heated Catalyst Efficiency Below Threshold (Bank #1)
P0424 Heated Catalyst Temperature Below Threshold (Bank #1)
P0430 Catalyst System Efficiency Below Threshold (Bank #2)
P0431 Warm Up Catalyst Efficiency Below Threshold (Bank #2)
P0432 Main Catalyst Efficiency Below Threshold (Bank #2)
P0433 Heated Catalyst Efficiency Below Threshold (Bank #2)
P0434 Heated Catalyst Temperature Below Threshold (Bank #2)
P0440 Evaporative Emission Control System Malfunction
P0441 Evaporative Emission Control System Incorrect Purge Flow
P0442 Evaporative Emission Control System Leak Detected (Small Leak)
P0443 Evaporative Emission Control System Purge Control Valve Circuit Malfunction
P0444 Evaporative Emission Control System Purge Control Valve Circuit Open
P0445 Evaporative Emission Control System Purge Control Valve Circuit Shorted
P0446 Evaporative Emission Control System Vent Control Circuit Malfunction P0441 and/or P0446

Apr 02, 2014 | 2000 Toyota Avalon

2 Answers

Trouble code po420 2007 solstice


P0420 - Catalyst System Efficiency Below Threshold Bank 1xicon.jpghttp://engine-codes.com/p0420.htmlForum CodePossible 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.

Jul 06, 2012 | 2007 Pontiac Solstice Convertible

2 Answers

I got a code P1150 only 2000 Sienna LE, which I guess means Bank 2 Sensor 1. I am looking at Denso replacement part. It has upstream left (234-9007) and upstream right (234-9009). Is bank 2 sensor 1,...


Ravi, I also have the same issue and confused between upstream left and right location.


I have problem with bank 2 sensor 1 and want to purchase a part. There are two part numbers 234-9007 for upstream left and 234-9009 for right.

So not sure the one on radiator (bank 2 sensor 1) side is upstream left or upstream right.

If you already know can you please reply?

Apr 10, 2012 | Toyota Sienna Cars & Trucks

3 Answers

My check engine light came the code is p0420


Technical Description

Catalyst System Efficiency Below Threshold (Bank 1)
What does that mean?

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.
Symptoms

You will likely not notice any drivability problems, although there may be symptoms.
Causes

A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings

Possible Solutions

Some suggested steps for troubleshooting a P0420 error code include:

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.

Thanks for using FixYa - a 4 THUMBS rating is appreciated for answering your FREE question

Sep 07, 2010 | 1996 Chevrolet Blazer

2 Answers

2002 Ford Windstar Error Code P1131 And P1151


those two codes are for the o2 sensors. both are the upstream sensors on the front and rear banks. so they are desinagted bank 1 sensor 1 and bank 2 sensor 1. them most common cause for this is faulty o2sensors , bad gas and of a poor running engine. so if your car runs good (no misfire) and gas is ok then replace the o2sensor witch is the very most common cause.

Jan 28, 2010 | 2000 Ford Windstar

1 Answer

I OWN A 2002 DODGE INTREPID AND IT COMES UP WITH THESE CODES P0700,P0056,P0135,P0141,P0155,P0161 CAN YOU TELL ME WHAT THEY MEAN?


po700 is automatic transmission fault detected. poo56 is didnt see .po135 is upstream heated o2sensor heater circuit fault bank 1. po155 upstream heated o2 sensor heater circuit fault bank2.po 161 is downstream heated o2 sensor heater circuit fault bank 2.

May 15, 2009 | 2002 Dodge Intrepid

1 Answer

Need info on codes PCM.P0134 and P0420


Both codes are for the oxygen sensors.
P0134 oxygen sensor on bank #1, sensor #1 is bad.
P0420 oxygen sensor on bank #1, the sensor down by the catalytic converter, is also bad.

Mar 26, 2009 | 2003 Honda CR-V

1 Answer

Code P0420


P0420 Catalyst System Efficiency Below Threshold (Bank 1)

There is one 02 sensor in front of the catalytic converter (called upstream), and one behind it (downstream). When the engine is warmed up and running normally the upstream oxygen sensor reading fluctuates and the downstream one is fairly steady. In the case where both readings are fairly steady, a P0420 check engine light code is set.

Possible Causes:
Oxygen (O2) sensor not working correctly
Damaged or leaking exhuast (pipe, manifold, catalytic converter)
Damaged catalytic converter

Mar 24, 2009 | Chrysler Concorde Cars & Trucks

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