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Catalyst monitor whereisitlocatedon1998dodge15005.2liter

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The computer uses the O2 sensors to monitor the performance of the cat.

Posted on Jul 13, 2013


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Where is the downstream oxygen sensor located on a 2000 nissan altima 4cylinder?

It is located after the catalytic converter. It is really called a catalyst efficiency monitor. If you have a fault code P0420 that translates to a catalyst failing, then the sensor is likely not the problem, instead the catalyst is worn out and in need of replacing, they have a lifespan of about 100,000 miles.

Sep 21, 2016 | Nissan Cars & Trucks

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Code P0157

OBD II P0157 due to Oxygen Sensor Circuit Low Voltage (Bank 2, Sensor 2)
This code refers to a fault in the post-catalyst o2 sensor on Bank 2. First, a basic run-down of the catalyst: The Catalytic Converter is used to help control tailpipe emissions, to "clean up" the exhaust, if you will. The PCM (Powertrain Control Module) uses the signal from the heated oxygen sensor to the rear of the catalyst to monitor the catalyst's efficiency by comparing it to the o2 sensors in front of the catalyst.

Read more at:

P0157 O2 Sensor Circuit Low Voltage

Mar 11, 2016 | 2007 Honda Odyssey

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Po422code coming up

Hi there:

DTC P0422 Main Catalyst Efficiency Below Threshold (Bank 1)
A vehicles' catalytic converter (catalyst) helps improve tailpipe emissions by oxygenating the exhaust gasses. It helps convert hydrocarbons (HC), Carbon Monoxide (CO), and oxides of Nitrogen (NOx) into water vapor (H20), Carbon Dioxide (CO2), and Nitrogen (N).

The PCM (Powertrain control module) monitors the catalyst efficiency by means of a post-catalyst Oxygen sensor. This sensor is used primarily for this purpose. It should switch much slower than the front oxygen sensors. If at any point the PCM detects that the post-catalyst o2 sensor is switching too rapidly (indicating no change between the inlet and outlet of the catalytic converter) it interprets this as a catalyst that isn't functioning properly.

Bank 2 is the side of the engine that has cylinder #1.

Symptoms of a P0422 DTC may include:
Increased tailpipe emissions
MIL (Malfunction Indicator Lamp) illumination

Potential causes of a P0422 code include:
Bad or non-functional catalyst
Engine operating out of optimal air:fuel ratio

Possible Solutions: Catalytic converters contain precious metals like platinum, palladium, rhodium among others. Basically, the cheaper the cat, the less precious metals used. It should be noted that there are some automobile makes that are very finicky when it comes to catalytic converters and the logic that the PCM uses to monitor them. Just because the parts guy says it will work doesn't mean that it will. The reason is that the engineering of the vehicle was done with a high quality catalyst in mind and it can't be replaced with a low cost catalyst. There are also different kinds of catalysts. Some makes will allow for a cheaper catalyst while others simply will not. Toyotas & Subarus are the most notorious for this. Subarus require CARB certified catalysts to keep the check engine light off and won't tolerate an aftermarket catalyst, no matter how expensive.

So basically if you have a recurrence of this code after replacing the catalyst with an aftermarket catalyst, this may be your problem. If you have this code and haven't replaced the cat, there's basically two likely causes: The catalyst is no good, or the engine is running out of optimal air:fuel ratio. A tune up or engine repair may correct it. Otherwise you'll need to replace the catalyst.

Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Aug 02, 2012 | 2001 Hyundai Elantra

1 Answer

Catulyst monitor and evap system monitor and oxygen sensor not ready also P0501 code

Diagnostic Test Code (DTC) P0501 "Vehicle Speed Sensor Range/Performance"
The Wheel Speed Sensor (WSS) generates a waveform with a frequency according to the speed of the vehicle. The signal generated by the WSS informs the ECM not only if the vehicle speed is low or high but also is stopped the vehicle or not. The ECM uses this signal to control the fuel injection, ignition timing, transmission/transaxle shift scheduling and torque converter clutch scheduling. Also the WSS signal is used to detect rough road driving condition.

Whenever Your OBD readiness monitors cannot complete it is because there is a problem that is affecting fuel mixture, ignition timing, or any other fault that can affect the level of tailpipe emissions. Once these faults are repaired, then the codes must be ereased so that the monitors can run and "re-test" the system to check for the same, or any other faults. The goal is for all the monitors to run and change to "complete" without any fault codes present.

In your case, the wheel speed sensor fault needs to be diagnosed and repaired so that the monitors will complete. Also note that one incomplete monitor can prevent other monitors from running. In your case, the catalyst monitor cannot run because the O2 sensor monitor is not complete. The catalyst monitor can only run AFTER the O2 sensors have received a "clean bill of health" from the O2 sensor monitor. The wheel speed sensor problem is keeping the O2 sensors from being tested.....So the wheel speed sensor problem is pretty much causing the whole thing.

Here's the kicker...If the vehicle has been driven in this condition for a period of time, there may be damage to the catalytic converters. The computer does not know this yet because the catalyst monitor cannot run. So it is possible that you can fix the wheel speed sensor thing, the O2 sensor monitors will complete, then when the catalyst monitor runs it could set a "catalyst efficiency" code. Then you will have to replace your catalytic converter to fix that. I'm not saying that this WILL happen on your vehicle, I am just saying that it CAN happen so you will not be confused IF it DOES happen. I see this all the time, and I have had customers accuse me of doing something to their car so I could sell them a high-dollar catalytic converter. This is simply not the case...I had no way of knowing that the converter had a problem because when I first received the car, the catalyst monitor was incomplete and there was not catalyst code present at the time.

So the only way to do this is to correct ALL fault codes one at a time until all monitors are complete and no fault codes are present.

Sep 17, 2011 | 2004 Hyundai Elantra

1 Answer

Where is bank 2 sensor one on a 2004 cadillac SRX

Two sensors per bank are used, one before the catalyst and one after. This is done for a catalyst efficiency monitor that is a part of the diagnostic system of the engine controls. The one before the catalyst measures the exhaust emissions right out of the engine, and sends the signal to the ECM about the state of the mixture as previously talked about. The second sensor reports the difference in the emissions after the exhaust gases have gone through the catalyst. This sensor reports to the ECM the amount of emissions reduction the catalyst is performing.

Generally, O2 sensor is on driver side 2nd one back...


Hope this helps.

Sep 04, 2011 | 2004 Cadillac SRX

1 Answer

I am looking for a diagram of where the oxygen sensor is

Some models have two sensors, one before the catalyst and one after. This is done for a catalyst efficiency monitor that is a part of the OBD-II engine controls. The one before the catalyst measures the exhaust emissions right out of the engine, and sends the signal to the PCM about the state of the mixture as previously talked about. The second sensor reports the difference in the emissions after the exhaust gases have gone through the catalyst. This sensor reports to the PCM the amount of emissions reduction the catalyst is performing.


Fig. 4: Typical oxygen sensor locations-3.0L OHC (4 valve) engine (click over pic for zoom)

Hope helps.

Apr 06, 2011 | 1996 Ford Taurus

1 Answer

Vsc and check engine light is on . Had it read and code p0420 came up. Autozone said it could be an air leak in exhaust, AF sensor error, fuel system fault or faulty catalytic converter. Is there a cheap...

DTC P0420: Catalyst System Efficiency Below Threashold (Bank 1)

The ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor its efficiency. The first sensor, and Air Fuel ratio (A/F) sensor, sends pre-catalyst A/F ratio information to the ECM. The second sensor, a heated oxygen sensor (O2S), sends post-catalyst information to the ECM. The ECM compares these two signals to judge the efficiency of the catalyst and the catalyst's ability to store oxygen. During normal operation, the TWC stores and releases oxygen as needed. The capacity to store oxygen results in a low variation in the post-TWC exhaust stream as shown below.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor slowly switches between RICH and LEAN. If the catalyst is deteriorated, the waveform will alternate frequently between RICH and LEAN. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the catalyst output becomes more variable. When running the monitor, the ECM compares sensor 1 signals (A/F sensor) over a specific amount of time to determine catalyst efficiency. The ECM begins by calculating the signal length for both sensors (for the rear oxygen sensor, the ECM uses the output voltage signal length). If the oxygen sensor output voltage signal length is greater than the threshold (threshold is calculated based on the A/F sensor signal length), the ECM concludes that the catalyst is malfunctioning. The ECM will turn on the MIL and a DTC will be set.
Hope this helps :)

Oct 19, 2009 | 2005 Toyota Highlander

1 Answer

Monitor Reset

The following conditions must occur to complete a Trip and test all OBD II monitors and components including the Catalyst Efficiency Monitor:
-- The misfire, comprehensive component, and adaptive fuel monitors are checked continuously from engine warm-up and can complete any time.
-- The exhaust gas recirculation (EGR) monitor test requires a series of idles and accelerations.
-- The heated oxygen sensor (HO2S) monitor requires a steady speed drive for approximately 1 minute at 30 to 40 mph.
-- The catalyst efficiency monitor requires a steady speed drive for 1 minute and 20 seconds beyond the HO2S monitor test at 40 to 65 mph.
If you cut engine off before test are completed then you must wait for a 6 hour cool down before monitors will run again.

Feb 06, 2009 | 1996 Nissan Quest

1 Answer

Engine Management Light

If you have an exhaust leak before or after the catalytic convertor, then the response of the of the sensor could be slowed.

An excerpt from Wikipedia:
Location of the probe in a system
The probe is typically screwed into a tapped hole in the exhaust, located after the branch manifold of the exhaust system combines, and before the catalytic converter. New vehicles are required to have a sensor before and after the exhaust catalyst to meet U.S. regulations requiring that all emissions components be monitored for failure. Pre and post-catalyst signals are monitored to determine catalyst efficiency. Additionally, some catalyst systems require brief cycles of lean (oxygen-containing) gas to load the catalyst and promote additional oxidation reduction of undesirable exhaust components.
It's a good article about the two-sensor system and oxygen sensors in general and is available here:

Jul 17, 2008 | 2002 Hyundai Accent

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