Hello All,

This is my first post. Hopefully you guys will be helpful. I drive 2001 Honda Accord coupe EX. 2.3L 4 Cylinder. So I got the check engine light on few months ago and went to autozone and found out the error code P0420. I did not want to spend the money on fixing the car at that point. the light use to stay on for few hundred miles and then go away for short duration and come back again.

Fast forward few months the light stays on all the time. I have to do the Texas annual vehicle inspection in a month so decided to fix the car. Went to Auto zone again and this time I got three error codes P0420, P0135 and P1739 :O. I also notice that the car mileage had drop down recently (which I didn't notice during the first inspection). I read some online forum and feel that the O2 sensor 1 (bank 1) is bad. I am not sure about the catalytic converter.

I have fixed some minor issues with car (changing the power window regulator, door lock actuator) but nothing major. I am not sure if I should try to fix it myself or bit the bullet and take it to a shop. I do want to do some diagnosis myself before taking the car to a shop.

Any advice or help will be great. Description of the error code is given below

P0135
A/F Sensor 1 heater system Malfunction

Probable cause
Open or short circuit condition
Poor electrical connection
Faulty A/F Sensor 1

P0420
Catalyst system efficiency below threshold bank 1

Probable cause
A/F ratio concern
Air leak near Ho2s (heated oxygen sensor) Bank 1
Ignition system concern
fault catalytic converter

P1739
Automatic transaxle concern (nothing else mentioned)

Thanks a lot

 

P0135 (O2 sensor preheater) should be easy. You can find that sensor up front, screwed into the exhaust manifold. Unplug the wire, & find the 2 same-color (black?) wires and measure continuity between those 2 pins in the plug. You're measuring the sensor side, not the car side of the plug. Should be 10 to 40 ohms. A burned-out heater usually reads open-circuit.

Replacing that sensor is easy, just unscrew it & screw the new on in it's place. Place like AutoZone will sell/rent/borrow a socket just for that, which allows the wire to pass alongside the socket.

Make sure you know whether you have a ULEV engine or not. That front O2 sensor is different and not all parts stores know that. The exhaust manifold looks different for the 2 engines, I'll post a couple pictures.

The P0420 might just be related, so wait & see if that one goes away with a new sensor.

I don't know much about automatic transmissions, so hope someone else chimes in there.

 

Here's the exhaust manifold for the normal engine (F23A1)
Sensor is #6

 

Here's the exhaust manifold for the ULEV engine (F23A4).
Sensor is #9.
If you have this engine, make sure the parts store knows about it, and make sure they list it as a different part # for the sensor.

 

Hopefully, a new forward O2 sensor or A/F sensor will resolve all your problems.

P0420 can be a troublesome code to resolve. Figuring out whether other problems besides the converter are causing takes time and patience. You may be able to reset the ECU and get by long enough to get your new emissions sticker check.

If code P0420 returns, inspect carefully for exhaust leaks and shake the converter (cold) vigorously and listen for rattling. Exhaust leaks need repair but any loose parts in the converter indicate the matrix has broken up and mean a new converter is necessary. There are some bolt-on replacements available, but check OEM price first to see if it's reaonable.

good luck

 

Thanks Jim and Texas Honda. I will replace the sensor and hopefully that should take care of first two error codes. Any idea on what might be causing P1739.

 

Like I said, don't know autos very much. But one standard response is...

How is the transmission fluid? Clean/dirty/smelly? Honda automatics do not like to be "power-flushed". Drain & fill only. And use Honda ATF, not Dexron or generic stuff.

 

P1739 is for the 3 clutch pressure switch.

How much testing are you ready for.....If you have a volt meter, measure the voltage on the wire with the key on - What is the reading?

 

Which wire are you talking about?

 

The one to the 3rd clutch switch? I'm jumping way ahead of the true testing procedure but why not

EDIT: or maybe you are wanting a pic of the location of the switch? Here.