Skatefrench

2001 Honda Civic HX ULEV (with California Carb sticker).

Last week CEL came on- Code P1166- Primary HO2S (No. 1) Heater System Electrical. I checked, and Lean Burn would not engage- which makes sense if there's a problem with the primary O2 sensor.

I reset the codes, and the light came right back on. I pulled the plug for the primary sensor and tested resistance of the heater circuit- there was no continuity- so I assume that sensor is bad.

With this vehicle model, there are a lot of problems with the wrong aftermarket O2 sensor being spec'd by parts stores- they spec a normal O2 sensor, while this car actually uses a Lambda sensor- wideband O2 sensor if I understand correctly.

So I did hours of research online, looking for the correct part- and finally came up with Denso 234-9005. Almost everywhere I've looked shows this as the correct sensor, including forums with personal experiences.

I also called the Honda dealership and got the Honda part#- 36531PLE305. This part cross-references to 234-9005 on multiple sites (including Denso's website).

I purchased the Denso part off Ebay for about $90, got it, installed it, and that's where the fun begins.

I reset the CEL, and the light has not come back on- which to me indicates that the heater circuit problem is fixed.

Now the problem:

The car runs terrible. At idle it wants to die, and it sputters along at highway speeds. These are the symptoms currently:

At idle, primary O2 sensor voltage periodically drops from 1 to about 0 and the car stutters and wants to die. I can pump the gas pedal and eventually get it to pull out of it.

At idle, short term fuel trims are both 46.9 I believe (which I'm assuming is maxed out). Long term fuel trim is slowly increasing to match Short term.

If I unplug the primary O2 sensor, both fuel trims drop to zero, and the car runs normal.

At slow speeds (25ish), O2 sensor reads about .6, and on a downhill stretch in 3rd gear, leanburn seemed to engage (it was at a time when it didn't feel like it should have, I've driven with lean burn for about a year now, and this was weird). Punching the gas didn't seem to kick it out of Leanburn as it would normally.

At highway speeds, O2 sensor is pegged at 1 the whole time- leanburn will not engage normally.

Leanburn somehow engaged while I was at highway speeds, and it felt like I lost almost all power- car immediately started slowing down and I had to punch the pedal to the floor probably 8 or 9 times over about 30 seconds to get it to drop out of lean burn- pretty sketchy on the highway.

At idle, if I punch the gas, the graph of the O2 sensor drops down to close to zero, then climbs back up to 1- is this how it should function?


My only 3 thoughts are-

- Could it be the wrong O2 sensor despite all the sites that seem to think it's correct?

- Could this O2 sensor be faulty? I've heard bad stories about EBay parts- it came in a box, inside a bag that had been opened, although the sensor did appear new. I do smell some sort of burning electronics smell under the hood- which i'm assuming is coming from the O2 sensor. I read that sometimes resistors in the sensors go bad? Could that be the case?

- Is it possible that the sensor signal wires are reversed? Doesn't seem likely, but it does seem like whatever the O2 sensor is telling the car is wrong, maybe even backwards of what it should be telling the car?


-OR is there some other underlying problem that's causing this problem??

Please help- I can't tell you how frustrating this has been.

ezone

From the sounds of it, I'd suspect the new sensor is bad..... or maybe has been contaminated.

GentleBen

I realize that this is an old thread and hopefully you found the solution to your problem. Posting the following in hopes that it may help someone. I know how frustrating these unknowns can be.

We too have a 2001 Civic HX ULEV. When the CEL came on with a P1166 code I had no clue what it could be. As you said it was Primary HO2S (No. 1) Heater System Electrical. By researching, the first thing to check was the resistance on the Air/Fuel Sensor located in the exhaust manifold just above the catalytic converter and conveniently in sight and easily in reach as soon as you open in hood. Using a multimeter to test the heater circuit in the AFR sensor yielded a reading of zero, zilch, nada. So that tells me that this sensor may work fine when it reaches operating temperature of over 600 degrees F (which it was) it was not going to pass state emission inspection.

Time to order a new one. The challenge was getting the correct one for this car.
Majestic Honda indicated that 36531-PLE-305 was the correct sensor. And yes, it is the more (much more) wide band one.The bad news was that the price was $311.08 +shipping. Surely there must be a less expensive alternative.

Ah yes. Denso Products.com had this same sensor (#Den 234-9005) for $135.79.
Amazon listed this same Denso sensor for $99.99!
All three sites said that this was the right sensor. So I took the plunge and ordered the Amazon sensor, knowing that others have ordered sensors that were supposedly the 'right' one only to find out that they weren't.

The sensor arrived in Denso labeled box and sealed plastic bag. It looked identical to the one that was in the HX except there were no numbers on the sensor itself. Hummm? Not a good sign?
Removal of the old sensor was easy. Shot some PB Baster on it and waited a few minutes knowing that some have had problems getting these off. Used a 7/8" sensor socket with 3/8'' drive. There was not enough room to add a 3/8' to 1/2'

GentleBen

...inch adapter for the 1/2" ratchet wrench. Slipped a short piece of pipe on the 3/8" ratchet and off it came with no struggle, no problem. Installed the new sensor with some antiseize on the threads.

Started the car and right away there was no CEL light! It was running normally and smoothly (as before) and still is. Also just passed inspection.

GentleBen

The car is still running well with no Check Engine Light.
If you get a CEL with the 1166 code or other O2 Sensor code I would use a multimeter to check the heater circuit for resistance.
In this case it was the two black wires (on the Air/Fuel Sensor itself). If there is no resistance the heater circuit is shot and the sensor will have to be replaced before inspection.

You can go to the stealership and pay mega bucks or...
use due diligence and find the right O2 sensor or Air/Fuel sensor and this is a relatively easy repair and need not be excessively expensive.

onetwoothreee

I had a similar experience after the CEL came on in my 2004 Civic Dx. The auto parts store ran a diagnostic (which they do for free) and the car produced code P0135 for bank 1, sensor 1 heater circuit malfunction. I rented an O2 sensor socket set (deposit + full refund after return) and bought a cheap O2 sensor online that didn't work. The CEL was back on the same day, and it ran even worse than before. The Denso 234-9005 is the correct sensor for this car. I got a Denso sensor packaged in a Denso box with instructions and anti-seize shipped to me for about $100 on Amazon and it works.

GentleBen

It pays to do a little research and get the correct one.

Glad that you were able to successfully replace your sensor.