Check Engine Light on and I got the Code, HELP

[MorganG]

So I started a thread about being hard to start on occasion that can be found here (
http://www.explorerforum.com/forums/showthread.php?p=1517745#post1517745 ) and I will post the text at the bottom of this post.
The updates to the problem are as follows:

1. Vehicle check engine started to stay on all the time, where it used to only come on if the car wouldn't start and then once it started it would turn off.

2. used an OBDII and got this code

P0155
02 Sensor Heater Circuit Malfunction (Bank 2 sensor 1)

3. My friend did call back after she picked up her car and I posted on here to ask the tech if he checked the ECT and he said he did and knew that it was not the problem. But the thing is he can't find the problem and the car wasn't mis behaving (naturally of course) when she took it in so how can he feel comfortable saying I don't know what's wrong with your car but I know it isn't that.

4. I cleared the check engine light and the next day it came back on. The car is starting to run sluggish and is getting worse gas mileage,

I still think it could be the ECT, anyone have some words of wisdom?

orig. post

Hey guys, I am new here, just trying to help a friend out,

She has a 2000 2dr Auto Explorer with the 4.0 I am assuming. She has taken it the shop 2x and they have not been able to reproduce the problem and can't really offer her much other than bring it back next time it does it.

The problem is occasionally she will go to start the car (cold start) and it will crank but not start. If she gives it gas, full throttle, it may on occasion start but idling really rough and she cuts it off. Most of the time the car starts fine. They have checked her fuel system but as far as I know nothing on the car has been replaced. The check engine light comes on during the malfunction, but after she lets the car sit (half a day) it starts up with no problems and no check engine light.

As far I can tell from what she has told me there is not really a rhyme or reason to when this happens (aside from it being a cold start), its only on occasion, about 2-3 a week. Seems to happen on the weekends, when she actually wants to go somewhere and not work

I was just hoping maybe the masses would know, have seen this as a common problem, have had it happen themselves etc., any thoughts would be appreciated

 

[410Fortune]

the heater circuit for the 02 sensor in question is likely bad, this usually is inside the 02 sensor but not always.
I would check the wiring going to the 02 sensor and if it looks fine replace the 02 sensor
Heater circuit malfunction means the computer is trying to pre heat the 02 sensor and its not able to get the signal through. 8 times out of 10 this points to a bad 02 sensor.

How many miles on this truck?

 

[MorganG]

73,000 miles

Ok so now for me to embarass myself

Aren't there a couple O2 sensors?
Can you point out to me where I would find this one?

 

[Runnin'OnEmpty]

Bank 2, sensor 1 is the one on the drivers side downpipe. It's accessed from under the vehicle, and not too hard to reach.

Welcome to the board, and please post back if this solves the starting problem.

 

[MorganG]

thanks for the replies gents, I am going to swap this out this weekend, might pop back in if I have any questions come up before then, thanks - MG

 

[MorganG]

Thank so much guys, installed the new 02 sensor on saturday, so far looks good. Engine starting and running smoother and the check engine light has not come back on yet. Not ablt to see if the gas mileage has improved yet since its only been a little bit but she did put atleast 90 miles on it so far and she is thrilled about how it is running now.

I don't know if this was the normal to do but I did and it worked, but after I installed the O2 sensor it still had the check engine light on so, I unplugged the battery for 10 minutes so the computer would be cleared, did that and when I started it again light was gone.

Thanks again - Morgan

 

[Corny1]

I have had the same problem with P0155 i replaced the sensor and code went but 1 day later came back?? , had the wiring checked found some small problems fixed them but light still comes on!! Driving me insane