Oxygen sensor questions

[Dave Sherman]

My girlfriend's 2005 Ford Escape with 140,000 miles just decided to throw a check engine light, and since she just spent $900 to have her exhaust replaced, she was a little concerned the shop damaged something. Muffler shop said the computer had to "get used to the new exhaust" and the light should go away on its own, which sounded mighty fishy.

Finally got a chance to look at it, and my scan tool showed p0054 and p0141 codes, which pointed to a problem with the downstream oxygen sensor heater circuit. When I looked underneath, I saw the cat is up near the exhaust manifold, and the muffler shop didn't touch the cat or either oxygen sensor. Wiring wasn't damaged. They just bolted up a new exhaust after the cat and downstream sensor. Since it was 140,000 miles and the sensor was original, I chalked it up to coincidence that the sensor decided to quit then, and she got her mileage out of it.

Cleared the codes, and at least the scanner is showing sensor data from the downstream sensor. Question: What do the fluctuating voltage readings mean? Second, the MIL light is off, and at least after a couple of drives she's saying it's still off. I would think if there was still a problem it would have lit up by now. Lastly, I went with a Bosch sensor from Autozone. It looked slightly different from the original, but the PCM seems happy with it so far and had no trouble installing it. I've heard conflicting reports on Bosch sensors, are they unreliable?

 

[eljefino]

The fluctuating voltage means the sensor's working. The "real math" is how fast the voltage moves compared to the front one, which shows the cat working or not.

If they welded they could have screwed something up with a dirty ground clamp, sending current through your o2 wiring that shouldn't have gone that way. It's probably not worth the fight with them, though. You might be able to get your buying the part at cost and them putting it in for free, for example.

 

[hansj3]

The voltage fluctuates from the ecu changing the Afr. High is lean, low is rich. If I remember right. If you were to graph it out it would look like an elliptical wave, its normal

 

[JTK]

All this means is the heating element on this particular O2 sensor is no longer working. You have to replace the O2 sensor. I've had this happen on vehicles much newer/fewer miles. I'm not sure which brand of sensors this particular vehicle prefers, but I'd research that before buying a replacement.

 

[Bottom_Feeder]

Originally Posted By: Dave Sherman
Lastly, I went with a Bosch sensor from Autozone. It looked slightly different from the original, but the PCM seems happy with it so far and had no trouble installing it. I've heard conflicting reports on Bosch sensors, are they unreliable?

"Bosch O2 sensors are garbage" is one of those things you read online all the time yet nobody seems to have any bad first-hand experience with them. I would not anticipate any trouble unless you have specific information. Even then, for example, my Subaru was supposed to be picky about O2 sensors but had no problems at all with the Bosch ones I installed.

Are Bosch sensors quality parts? Yes.

Are some cars picky about the brand of O2 sensors used in them and may not like Bosch? Yes.

 

[Dave Sherman]

I doesn't look like they had to weld anything, the new pipe is just bolted to the outlet of the cat, and the two sections of the exhaust are just slid together and clamped.

I already replaced the sensor myself since it didn't look like they caused it. It was only $43, and other than banging my wrist into the frame (ouch) when the old sensor let go, not too hard to replace. Just hoping that code doesn't come back and that she can pass the e-check when it's time.

 

[eljefino]

The o2 sensor heater readiness monitor runs within the first minute of the first time you turn the car on. I bet you're golden.

 

[zzyzzx]

I have over 140K miles on a Bosch O2 sensor in my Escort, and as far as I can tell, it seems to be working just fine.

 

[Trav]

Using an air chisel anywhere on the exhaust can shake an old heater element in an O2 loose. It happens and there isn't much you can do about it.
The heater circuit failed not the O2 sensing circuit itself but it needed to be replaced to keep the CEL away. Bosch sensors are good quality, no problem with them.

 

[artbuc]

Originally Posted By: Bottom_Feeder

"Bosch O2 sensors are garbage" is one of those things you read online all the time yet nobody seems to have any bad first-hand experience with them.


You have not read enough Toyota/Lexus forums. Many first hand experiences of problems with Bosch AF and O2 sensors. But, as you also posted, it may be due to incompatibility vs inherent quality. However, IMO, if Bosch makes a sensor for T/L vehicles that do not work, that IS a quality issue.

 

[slacktide_bitog]

Bosch o2 sensors aren't garbage when they're OEM. For some reason, aftermarket Bosch is far inferior to Bosch's OE parts.

 

[HerrStig]

I just stuck a Bosch "front" sensor in a Camry. It was a good buy, but we'll see if it quickly develops "lazy sensor" syndrome.

 

[Vikas]

Bosch also repackages O2 sensor. So if your Bosch sensor says "Made in Japan", it will be either Denso or NTK and that will work great on a Honda/Toyota.

 

[ltslimjim]

^This. The older "Honda Genuine" 5-wire on my previous Honda was over $600 from the dealer. When Bosch got the deal, they started re-selling them for $350 or so. lol

Then, I found NTK/Denso 5-wire replacements for $150 or so on Amazon. Thankfully, I got a SMP re-labeled OE sensor Made in Japan for cheap before SMP realized they were selling them too cheap.

I paid $55 or so.

So, each app is really anyone's guess until you get some reliable information.