Philip54

The engine light is on and I scanned both the P0134 P0420 codes. Under P0134 the scanner reads: 'O2 sensor circuit no activity detected Bank 1 Sensor 1.
Is most likely a sensor issue or a catalytic converter issue?
Thanks

Wankenstein

https://www.obd-codes.com/p0420
https://www.autocodes.com/p0134_honda.html

Check for manifold and other exhaust leaks.
Any idle or performance issue?

ezone

Fix the O2 sensor code first.
Then drive it and see if the cat code returns, and deal with it then.

Philip54

Thanks for your reply. No idle or performance issue. The car actually runs pretty well.

Philip54

Thanks for your reply. Both my sensors and catalytic converters are relatively low time and I am trying to avoid purchasing unnecessary parts. This is why I am trying to troubleshoot the reason for the engine light and replace only the component that has failed.

ezone

Doesn't matter.
It's set fault codes now.
Find and fix code P0134 first. (It may or may not be a failed O2 sensor, but it's usually a failed O2 sensor)

Philip54

Thanks. We'll try the sensor first.

ezone

If you are going to replace it, get a DENSO or NTK sensor.
Whichever brand the factory installed....I think it was denso but not positive.

ezone

For 02 Si with K20 engine....It's an A/F sensor, not a regular oxygen sensor. OEM was indeed Denso.

HONDA part # 36531-PND-A11

DENSO website, look up your own part#: http://densoautoparts.com/find-my-part.aspx

Denso # 234-9004 ....now search for that at your local parts stores or online?

Philip54

Thanks for the additional information. That really helps. I kind of remember that on that engine there is not a regular oxygen sensor.

Philip54

I replaced the A/F sensor with a new Denso sensor. The engine light stayed off for about 1,500 miles, but now it is back on. Is there any way that the new Denso sensor can be tested out of the car? Also, assuming that the sensor is good, what should be the next step to troubleshoot the engine light on (the error is still the same: P042).

Thanks

ezone

So the AF sensor code is not present now. Only the cat code is returning?
Probably needs a cat.
If it doesn't have to pass an emissions test anytime soon, I might erase the cat code and then see how long (miles) it takes to reset it.

PS, in your first post you listed both codes were found......That means it already had set the cat code before it set the sensor code.

Philip54

Yes, only one code this time. I also think that a new cat may be needed. But the strange thing is that the people that replaced the AF sensor said that the sensor was shot (it was not providing heat, perhaps the wires that provide the heat were broken). That is why I would be interested in removing the sensor and test it, if that is possible).
Also, is there any risk of damaging the engine driving the car with the light on for a while?
Thanks

ezone

No.
Google search P0134, read the DEFINITION of that code..... that tells you how the sensor failed.

You want to pull out the brand new working AF sensor? NO!!!!
It's working fine according to the computer. DFWI

I hope you meant checking the old bad failed AF sensor.
Forget it. You can't check for P0134 off the car.
If you had a P0135 code you could check heater circuit resistance off the car, that's about all you can check.

Philip54

Thanks for your reply and clarifications. I erased the engine light and I'll drive the car for a while to see if it comes back. Then I'll make a decision about the cat.