2001 Civic HX Lean Burn and AFR Sensor Problems - Fuel Economy, Hypermiling, EcoModding News and Forum

skatefrench · 08-15-2016, 09:51 PM

Hey! I'm not sure if this is the right board for this. I think this problem is somewhere between eco-problems and just general car problems.

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

I'm using a bluetooth OBDII device to monitor lean burn on my phone with Torque app, and can verify that this vehicle does use lean-burn mode (I read some other threads a while back where it was debated weather the CA cars had lean burn enabled or not).

Here are the details:

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. 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.

Mod- sorry if this is in the wrong spot.

Ecky · 08-15-2016, 10:18 PM

I'm leaning toward the O2 sensor being faulty. I picked up a cheap downstream O2 sensor for my Insight when RockAuto was having clearance on them, just to have a spare, and when I tried it I immediately got a CEL, because it disagreed with the upstream sensor. Of course, the only way to know for certain is to swap in a known-working sensor.

skatefrench · 08-15-2016, 10:30 PM

Ecky, thanks for your thoughts. That's what I'm thinking, too. I guess the fact is there are 2 different circuits in the sensor- the heater and the sensor, and it perhaps this fixed the heater circuit problem, but introduced a new problem with the sensor itself.

Autozone has the same sensor for $156- I paid $90 for the ebay one, so I hate to pay more, but it's so frustrating I'm getting to the point where I don't really care that much, I just want it fixed. Thanks for you help!

Joggernot · 08-16-2016, 07:45 AM

Quote:

Originally Posted by skatefrench

...Autozone has the same sensor for $156- I paid $90 for the ebay one, so I hate to pay more, but it's so frustrating I'm getting to the point where I don't really care that much, I just want it fixed. Thanks for you help!

At Autozone you can take it back and get another one to try. You can also take it back, get your refund, and buy a different brand in the store. I've done that for sparkplugs that just didn't work in my car.

skatefrench · 08-17-2016, 12:41 AM

Hey that's good info, thanks! I'm not sure if they'd be as quick to take a return on a $150 O2 sensor vs a $10 spark plug, but it might be worth a try. I already ordered the same sensor (234-9005) off amazon for $98. Both ebay and Amazon list the sensor as the correct one for my car, so it should be an easy return if it doesn't work, cause either it's incorrect fitment, or its faulty. Already started the return on the ebay part. Hope that goes smoothly.

skatefrench · 08-18-2016, 11:55 PM

Hey, just want to give an update. Thanks to those that offered input. I received the new AFR sensor today via Amazon. The part number is the same as the first one I ordered- Denso 234-9005. I installed this one and the car runs perfectly now. Lean burn works as expected and all is well with the world.

SO. To anyone who is looking for answers:

2001 Honda Civic HX w/ ULEV and CARB sticker, the correct upstream AFR sensor is Denso Part 234-9005. It is a 4 wire sensor, and can be purchased from Ebay or Amazon for under $100. I checked with the dealer, and their price is $450.

The original Honda part number is 36531PLE305. The stamp on that part says DU2 Denso 192400-1030. This part cross-references to the Denso part 234-9005.

Hope that can help anyone looking for O2 sensor info on this car.

California98Civic · 08-19-2016, 02:23 AM

Nice write up. Great final reference info. Glad you were able to fix it. Really satisfying to fix it yourself, eh?

darcane · 08-19-2016, 01:28 PM

Quote:

Originally Posted by skatefrench

Hey, just want to give an update. Thanks to those that offered input. I received the new AFR sensor today via Amazon. The part number is the same as the first one I ordered- Denso 234-9005. I installed this one and the car runs perfectly now. Lean burn works as expected and all is well with the world.

SO. To anyone who is looking for answers:

2001 Honda Civic HX w/ ULEV and CARB sticker, the correct upstream AFR sensor is Denso Part 234-9005. It is a 4 wire sensor, and can be purchased from Ebay or Amazon for under $100. I checked with the dealer, and their price is $450.

The original Honda part number is 36531PLE305. The stamp on that part says DU2 Denso 192400-1030. This part cross-references to the Denso part 234-9005.

Hope that can help anyone looking for O2 sensor info on this car.

For reference:

I have exactly the same car (Californian 2001 Civic HX - 5spd). in 2013 I purchased a Bosch 13680 Oxygen Sensor to replace to original. I've had no problems with that O2 sensor on mine. Currently available on Amazon for $88:
https://www.amazon.com/gp/product/B000BZEIKC/ref=oh_aui_detailpage_o01_s00