1997 Accord LX 2.2L changed oxygen O2 sensors P0135, P0141

[CheeseHead1]

Howdy folks,

I changed both oxygen sensors yesterday on my 1997 Accord and wanted to share my experiences.

Check Engine Light was on and I was getting codes:
P0135 - O2 Sensor Heater Malfunction Bank 1 Sensor 1
P0141 - O2 Sensor Heater Malfunction Bank 1 Sensor 2

Also, after clearing the codes, if I started the vehicle the codes would come on instantly. So it wasn't some kind of flaky electrical issue, it was consistent.

I did some reading in the forums and was wondering if the O2 sensors really had a problem, or whether it could be something else (maybe a fuse). I researched and it looked like Fuse 6 controls these two circuits, but it also controls the main computer (car was running great) and also the cruise control (which was working fine).

Given the age of the vehicle, I figured both sensors had probably gone bad.

The Haynes and Chilton both described diagnostic procedures on the O2 sensors. Again, given the age of the vehicle, I decided to skip this and just change at least one of the sensors.

I had read some comments on this forum or others that recommended getting the Denso part over the Bosch. Auto Zone and Advance Auto Parts both carried the Bosch but not the Denso.

I also wanted a true replacement part, not a "universal replacement" that would require me to cut wiring. I wanted to keep the wiring intact.

I was pleased to find the Denso parts at Napa, but be careful. I replaced the front successfully, only to find out what they had sold me for the front part had the wrong connector on it. The replacement part should have a female connector, but the one they sold me had a male connector. Of course I didn't identify this issue until I already had the new part installed!

Correct NAPA part numbers for Denso:
Front: 234-4620
Rear: 234-4601

*** Wrong part number from Napa for front: 234-4095 ***

The Denso parts from Napa were expensive. Even with a AAA discount it was $83 for front and $72 for rear. Napa was kind enough to let me return the incorrect part for store credit.

It looks like Parts Geek stocks them at partsgeek dot com. You have to pay for shipping, but it looks like you could save some money this way. It looks like their web site lists the correct parts. I haven't ordered from them, but saw them recommended by another poster.

Both parts were easy to identify on the vehicle. The front sensor, open the hood and look down, the O2 sensor is sticking out of the heat shield that covers the front exhaust manifold (a big aluminum plate that says "Hot" on it and shows a picture of a hand).

The rear sensor is visible from underneath, follow the exhaust system, the expansion bubble is the catalytic converter and it is sticking out of the rear end of the cat.

Removing/replacing the front was relatively easy. My Haynes manual recommended removing the old sensor while the exhaust system was warm, to make it easier to remove (the metal contracts slightly when cold). I used a special tool for O2 sensors, it is a deep socket but has a long slit cut along one side to allow the socket to fit over the wire. I believe the tool is a 7/8" socket, but don't quote me on that.

Before starting anything I sprayed both the old sensors good with PB Blaster, in the hopes that it would make removal easier.

I removed the front connector, there is a little tab you push down near the rear of the connector. You will hear a snap sound as it releases. Then still holding down the tab, wiggle the connector down until it becomes free. There is a metal bracket near the connector, it holds the male part of the connector (the part on the wiring harness you are not changing). So you can leave that bolt and bracket in place, it gives you something to pull against as you try to free the female end. It is a snug fit and did require some wiggling to get it to release (each time, I replaced and removed it several times).

Then I used the special socket with a 1/2" breaker bar and an adapter (it is a 3/8" drive socket) and the old O2 sensor turned fairly easily.

The new sensor should come with some anti-seize, it was a copper color and I would guess it is heat-resistant anti-seize. The mechanic strongly recommended the use of the anti-seize, otherwise he said the new sensor would be impossible to remove later. Make sure you only get the anti-seize on the threads, but not on the sensor itself.

Installing the front sensor was straightforward. Insert it and turn by hand until it is snug.

Neither Haynes or Chilton manual included a torque setting for the O2 sensor, at least I couldn't find it. An online manual at the shop said to use 33 foot-pounds so I did.

Then plug in the front connector and you should be all set.

I cleared the code and test-started the engine. The CEL came on immediately but when I checked the codes I was only getting the rear code P0141. Success in front!

The rear was more of a pain. Two main issues. First, the connector was hard to reach and hard to separate, that slowed me down quite a bit. Second, the O2 sensor was harder to release than the front. Minor third issue, the replacement wire was the same length but not the exact same part, so didn't fit in the support tabs/loops as well.

The connector is mounted on the front firewall. Follow the wire from the sensor to an aluminum cover, then toward the front of the vehicle. It is mounted up on the firewall kind of by the passenger feet. It is a tight spot and hard to get a good grip up in there. We could squeeze the tab and felt it release, but pulling in it, it did not want to come free.

Trying to figure this out, I took a good look at the front connector and replacement part. The connector looked the same, also a female connector on the rear sensor. There was a metal bracket holding the connector to the vehicle, I assumed this mean the male connector should be held in place and I should be able to free up the female end.

After more failed attempts to release it, I looked at the old part more closely. It looked like maybe I could use a screwdriver to break the release tab on the female connector. I tested my theory on the front sensor I had already removed, and it looked like it would work. So I went ahead and used a screwdriver to break the tab on the stuck connector, the female side (sensor side). Still wouldn't release.

I had thought about using some type of lubricant to try to free up the connector, but was hesitant to get it all slippery, that would make it even harder to get a grip on to remove. Finally I figured I needed to try some type of lubricant. I looked at PB Blaster and WD 40, but wanted something that I knew would not damage the plastic connector. I had some slicone spray that said it was OK for plastic, so I doused the connector liberally with silicone spray and let it sit for 15 minutes or so. (Probably you should have the battery disconnected before spraying.)

Then I also looked carefully at the front connector, to see where I could get a purchase on the female end of the connector, and wouldn't break anything on the male (wiring harness end) of the connector. I didn't mind breaking the old one if necessary, but wanted to be able to plug in the replacement. There was a little rectangle right at the bottom of the connector where the wires went in - I concluded that should be a safe part to grab with pliers and pull. I had a long handled "tongue and groove" pliers, and was able to grab that little rectangle and pull. Sure enough, the connector came apart! And thankfully, I didn't break anything.

Getting the wiring free was straightforward. There were a couple of little plastic tabs to push up out of the aluminum protecting plate. One had to be pried apart with screwdrivers, it had two sets of locking teeth.

The final challenge - freeing up the sensor itself. First I tried the special socket with a breaker bar. The old part was in so tight, it would not budge. The socket was spreading the opening and was slipping around the sensor a little. Now at this point I had sprayed PB Blaster on the area good about five times over 2 days. It didn't seem to have much effect.

A mechanic suggested cutting off the wiring from the end of the connector, seeing as how I was replacing it anyway. Then I could use a normal deep socket (which would be stronger). While cutting the wires, the outside end of the sensor came off as well. That was fine with me, now I had easy access to the rest of the sensor that still needed to be removed.

Now using a deep socket and breaker bar, the part came loose. It took a lot of pressure, be careful not to slip or injure yourself. Also I had the luxury of working on a lift. I'm sure it was easier working on a lift, but I think it would be doable with the front of the car lifted up on jack stands as well.

Installing the new sensor was straightforward. Again I used the anti-seize and torqued to 33 foot-pounds.

One minor challenge, the old wiring was thicker at 2-3 points where it attached to the support clips/bracket. But the new replacement wire was uniformly thin. You should be able to manufacture your own expansion cushion by using a piece of vaccuum hose, cut the size you need and cut a slit down the side to work it over the new wire. I didn't have any vaccuum hose available, so improvised and cut the old thick pieces out of the original wire, then used those to wrap/cushion the new wire in the connector points.

Another comment, the old wire had a protective sheath that ran all the way to the top of the sensor, but the replacement had about 3" of wiring showing at the top of the sensor. I was going to wrap it with electrical tape, but the shop mechanic said it should be fine with the four wires exposed for that length. Let's hope so!

Cleared the codes and started vehicle to test. No check engine light! Mission accomplished!

[jgilstrap]

Excellent article. I replaced both sensors last weekend. Advance Auto had both of the recommended Denso sensors for approximately $135, but that was with a $30 discount. Had the same problem with the wrong part for the front sensor (up stream) and had to make an addition trip to Advance Auto. The new sensor under the car (down stream) had a different O2 end than the Bosch that was installed. Advance Auto said it was just a different manufacturer and it would work. Both sensors work well.