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Discussion Starter #1
just got an OBD Fusion app, and of course had to use it. Shows on the CRV that sensor 1 and sensor 2 have different voltage reading, both around 2- 9 I think. My F150 rating are sensor 1 anywhere from .9 to .69, sensor 2 stay about 69-72. What readings should I be seeing if all is okay?
 

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O2 sensors and Air Fuel Ratio sensors work differently, so its important to know what you have. In this case, they should be O2 sensor on that generation CRV. Sensor 1 should bounce between somewhere around half a volt and 1 volt. Bank 2 should stay fairly steady on the lower end of that range if the sensor and CAT are working correctly. If there is a rich condition the voltage will be higher, and lower voltages indicate a lean condition.
 

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very simply DONT WORRY ABOUT IT. Every single vehicle will read differently and those tools are not accurate enough to tell you there is a problem unless check engine light is on.

This is why the invention of this being put to market is such a bad idea. People go nuts over them having not a single clue what their looking at.

That voltage reading means absolutely nothing without a proper scan tool because it does NOT just stay at set values, it oscillates.

If there is a problem, the check engine light will come on.

Sent from my SM-G950U using Tapatalk
 

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Discussion Starter #4
very simply DONT WORRY ABOUT IT. Every single vehicle will read differently and those tools are not accurate enough to tell you there is a problem unless check engine light is on.

This is why the invention of this being put to market is such a bad idea. People go nuts over them having not a single clue what their looking at.

That voltage reading means absolutely nothing without a proper scan tool because it does NOT just stay at set values, it oscillates.

If there is a problem, the check engine light will come on.

Sent from my SM-G950U using Tapatalk
There is a code saying the exhaust system is diminished (not exact terminology) so wanted to see a bit more. May be something I cannot even have fixed easily.
 

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What was the code?
 

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Discussion Starter #6
PO420 "catalytic system efficiency below threshold". 18 year old car I would expect diminished!
 

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Very possible. Especially if it has been running rich for some reason. But the sensor could cause the code if it isn’t reading properly. What do the numbers do on sensor 2 while running at operating temperature? If it cycles to match or nearly match sensor 1, it’s probably your CAT. If it just sits kinda high and sensor 1 is cycling within the range previously noted, I might suspect the sensor failing.
 

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Discussion Starter #8
Both sensors showed low voltage all the time, I ran some catalytic converter cleaner and both now show from low up to .60 area, with fluctuate. I'll look closer, but seems the number 2 is lower than number 1-- was using the vehicle while using the app so had to watch the road more!
 

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The rear one should be lower with little fluctuation. Voltage should climb if you stab the throttle in neutral, then drop back down if everything is working right. Also keep in mind when looking at those sensors that they don’t work until they heat up. So initially on a cold start they probably won’t do anything.
 

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Discussion Starter #10
I went out and with a cold motor started it up; with the cold engine the sensors shows no 1 .88-.27, No 2 about .94 steady. when the engine warmed up to. 180 degrees sensor one shows anywhere from .12 to .82 going and down; sensor 2 stayed around .8-.9 most off the time, when I accelerated to 2000 rpm it went to about .80, As I ran the engine I noticed that no 2 was lower most ion the time than no 1, a few times higher.

Still have the PO420 engine code popping up.
 

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Sounds like sensor 1 is working like it should. Usually when the converter is shot, sensor 2 will almost mirror sensor 1. I suspect that rear sensor may be failing. With it up to operating temp, pop a vacuum line off and watch the sensors. See if the voltage changes on sensor 2. If it still stays higher, I would suspect it’s failing even more.
 

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The pre-O2 sensor different than the post-O2, or at at least the ECU is looking for different readings to make sure the cat is doing it's job. When it's not, it sets the P0420 code for Catalyst Efficiency below Threshold. When the cat fails, the post-O2 sensor readings will mimic the pre-O2, setting the code.

It COULD be an O2 sensor, but most likely it's a failed convertor.
 

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The pre-O2 sensor different than the post-O2, or at at least the ECU is looking for different readings to make sure the cat is doing it's job. When it's not, it sets the P0420 code for Catalyst Efficiency below Threshold. When the cat fails, the post-O2 sensor readings will mimic the pre-O2, setting the code.

It COULD be an O2 sensor, but most likely it's a failed convertor.
What he has relayed is that the sensor value is staying constantly high, and not oscillating. Which is why I don’t immediately suspect the catalyst.
 

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Before we get too carried away with parts and since you like playing with your new scan tool, let’s look at a couple other things to rule out any other issues that may cause this. Find the long and short term fuel trim numbers and start it up. It will take a minute for the system to go into “closed loop” operation, at which point the computer will start to update the fuel trim numbers. The short term will bounce around a little and long term stay steady and update less frequently. Watch those numbers and take note of what they are at idle. Keep watching them and take it for a spin. Take note of the numbers again and let us know what you find. There is a possibility for other things going on that may not be bad enough to set codes, but could be affecting fuel trim enough to skew that O2 sensor.
 

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Discussion Starter #16
Just wondering, would be of any advantage to try to use a salvage cat converter? One from a car with damage to other than engine etc. Might save some money at the time but may be buying more trouble.
 

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Would be a gamble. But I wouldn’t change anything just yet. If there is something going on with it that could damage the catalyst that isn’t addressed, you will be in the same boat again. And I’m not saying yours isn’t damaged. But it should be fully checked out before swapping parts based on codes alone.
 

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You cant get actual oscillation data movement ON A CHEAP OBDII BLUETOOTH ADAPTER.

If you have a 0420 code TAKE IT TO A DANG SHOP.

Being that there is nothing of any substance for answering this is because no DIY person that doesnt have proper shop equipment (and a multi $1000s scanner/data link) is ever going to figure out.

Instead people throw parts at the problem till it is eventually fixed.
 

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I’m sorry, but you don’t need a $1,000 scan tool to diagnose a problem. Knowledge about what you are looking at and the will to try goes a long way. People ask questions because they want information so they can try to solve their problems effectively. So instead of telling someone they can’t fix their vehicle without thousands of dollars worth of diagnostic equipment and a shop full of tools, give them the information they ask for.
 

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Discussion Starter #20
tThe mechanic checked the cat, not with a scope, but listening and noticed a rattle. He is certain the insides are loose , and something is blocking the escape of exhaust, putting back pressure on the engine, thus affecting the shifting. I would try to change it myself, but a previous owner had one changed not with original design-- flanges on either end. Since it needs welding, back to the shop I go. Not just replacing parts to find what is wrong, he doesn't think the sensors area faulty but need too change the rear one if it won't come loose from the cat. He also noticed something I should have, a radiator leak, trying spray Flex Seal as a temporary fix right now. That I think I can change. Thanks to all for insights and recommendations.

As an aside, I saw an online video where a mechanic cleaned a converter with spray Sea Foam by ins-trad of putting it in the gas tank as usual, he removed the upstream O2 sensor, sprayed some in the opening, replaced the sensor and ran the engine a while. He did not say or show how much he sprayed in, looked like no more that five squirts. Doesn't seem enough, but maybe so.
 
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