Hello,

First of all I would like to thank everyone on the forum who has taken the time to post. In the last couple days I've been continually amazed at how many different topics are covered...and how many of these apply to my Explorer. On to my problem:

I have a 1997 Sport 4.0L SOHC V6 with 142k miles that has had a lot of work done on it recently (new transfer case to fix that chainsaw sound a bunch of other people have talked about on here, a new alternator, a new battery, new front and rear brakes, and a new stop light switch). Lingering problems include the high mount brake lamp not working (which I can live with since I can still pass inspection without it, and I am not going to pay $$$$ to fix it at the dealer since I can't do it myself), and my CEL staying on...

About five months ago the CEL came on, I read the codes and came up with the following:

P0135 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
P0141 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
P0155 O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
P0156 O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)

Since I was still a little broke from replacing the transfer case for $1100, I decided to wait before fixing this problem since my car still fine, even if it did idle a little wierd and conk out once or twice if it wasn't warmed up. Well, I finally replaced the four O2 sensors about a month ago and the CEL went away, however, within a week the CEL came back on. You guessed it, the same four codes are back, and my car failed inspection as a result. Dang.

My engine still idles a little wierd, but for the most part that problem seems to have gone away even though the CEL is still on. I am getting a little over 17mpg still, so that is a little low, but not terrible. I talked with my friend a mechanic and he told me it is the Idle Air Control Valve, so now I've ordered a new IAC valve from www.rockauto.com (great deal by the way) and I'm waiting for that to come in so I can replace it. I've read the excellent IAC replacement guide on here (amazing really), but since I don't have the tools to replace the IAC at home, I am going to take it in to my buddy and work on it with him at his shop.

That's where my question comes up: Does anyone have any experience with a problem like this, or does anyone have a recommended course of action for me to take? Why would my O2 sensors still come up with errors after I replaced them? Would replacing the IAC sensor help to clear up this issue and my idling problems?

THANKS in advance for anyone able to help out with this one. I hope I've been clear enough explaining the problem, but if there are any murky areas, I'll do my best to clear them up.

THANKS!

Tripp

 

Have you checked fuse 11 (15 amp mini fuse)under the hood in the power distribution box? It's spliced to all four O2 sensors

 

Check for a heatshield around the drivers side upstream HEGO sensor to have fallen off, worn through the wire and caused the heater circuit to short out and blow the fuse for the heater.

 

I will check on both of those this afternoon and let you know what I find out. Thanks for the quick response, I really appreciate it!

Tripp

 

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What is the HEGO sensor (is that the O2 sensor?), and what would the heatshield look like? Should I be looking for a frayed wire coming from the driver's side upstream O2 sensor?

Thanks,

Tripp

 

HEGO-heated exhaust gas oxygen. Check for a metal shield that may have detached from the exhaust y-pipe, and be hanging off the left side upstream oxygen sensor, and possibly worn through the wiring. If it's happened, you can't miss it.

 

Yes. HEGO is O2

 

Thanks for the clarification, I was pretty sure that's what it stood for, but I wanted to make sure of it. I'm not too experienced when it comes to working on cars, but I try to learn with every opportunity I come across.

 

Hey guys,

So I replaced the IAC valve, and checked the fuses in the power distribution box and still no luck. The fuses work fine, and the new IAC valve didn't do anything to fix the problem. I had the O2 sensors checked yesterday at the shop I go to, and they weren't operating at all (00000 readout on the diagnostic test). What would cause four brand new O2 sensors to burn out so quickly? I just put them in less than a month ago. Could it be that they were bad to begin with? I'm really at a loss of words here, and I have no idea why this problem persists, so once again any ideas/solutions would be greatly appreciated!

Thanks again folks,

Tripp

 

Has anyone checked for voltage at fuse 11? Did you crawl under & check the wiring as Canadaguy mentioned?

This makes no sense to me, but the wring diagram shows the O-2 circuit is spliced to the transmission controls. If you have an auto trans is it shifting normally?

Edit
Maybe one of the other guys will know what the difference is between PO-135/136 O-2 heater circuit fault and PO-155/156 O-2 circuit fault is and that might be a clue to this.

 

As 87XLT stated, that's the fuse that's common for all the O2 sensors heater circuits. I'll bet the fuse 11 input is dead. If the fuse is good, the trouble must be an open in the wiring upstream from the #11 fuse holder. Or it could be the #11 fuse holder itself.....

 

Thanks for the continued responses guys, I really appreciate the dialogue on my problem. I used one of those simple tools where you ground the wire coming out of it and then touch the tool to the fuses and if the light pops on the fuse is good (sorry for not knowing what this would be called...I didn't really grow up with cars, but I'm learning fast). So when I did that I got a light, but in terms of voltage...no idea. I crawled under the car too and found my shiney, new O2 sensor and checked the wire as well...looked good to me, there were no frays or visible damage.

Interesting you should mention the automatic transmission. I've noticed that there is a little 'hiccup' or stutter every now and then when it shifts both up and down. It doesn't make any noise, but the car hesitates just a touch.

I will check that driver's side upstream O2 sensor again this morning to see if there is anything I missed, so I will post on that once I clarify the issue. Thanks again for the responses guys, I really want to figure out this problem and finally get my car running well again...it's been way too long now.

 

When you used the test light to check the fuse, did you check for power on both sides of the fuse? You should check both the engine compartment and passenger comparment fuse panels, although I believe the fuse you are looking for should be under the hood.

 

Yepp, I checked both sides of the fuse, as well as all the fuses in the passenger comparment between the steering wheel and the door. All of them were working fine, but yeah, you're right, the fuse that concerns me is under the hood.