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Discussion Starter #1
Hey Guys-
Got some codes from my SES light yesterday. I think I need to replace my O2 sensors, but after talking to Silvapain, it seems wierd that all four would go at the same time.

Here's the scenario: Driving to brother's baseball game, take back road shortcut and have to go through a couple mud puddles. No problems. Go to the game, and on the way home, stop for Rita's crappy italian ice. After starting the car back up, my SES light comes on. Check codes yesterday afternoon, and get 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)
P0161 O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)

Does it seem wierd that all four went at the same time? I had Autozone clear the codes, but my SES light came on again this morning. Could mud have gotten into the O2 sensors and fried them? Can they be cleaned before I replace them?

JR
 

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I doubt the mud puddles are to blame, and I doubt there's anything wrong with the O2 sensors. If I had a wiring diagram with me right now I could tell you for sure, but it looks like since it's the heater circuit that's giving the problem in all of them, there is probably some sort of wiring / fuse / connector issue somewhere that's cutting off power to all 4 of them. Man I wish I had that diagram, but I bet the heater circuit starts as a single line and then splits to the 4 sensors, if this is true the problem would obviously be at or before where they split.
 

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Discussion Starter #3
I don't know about the mud puddle not having anything to do with this. It seems as though that was the only incident that would have caused a problem. Also, since the heater cicuit is part of the O2 sensor, and is wired into it, wouldn't that mean that the O2 sensors have gone bad? I don't know anything about this emissions crap...

JR
 

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The heater circuit may be part of the O2 sensor, but it is controlled by the computer and has to get its power from somewhere. Also the presence of these codes indicates that the O2 sensors are operating properly, just not being heated. Modern O2 sensors are heated only because that gets the computer into closed loop mode quicker, since the sensors can only operate correctly after they warm up. The chances that all 4 sensors failed at the same time are extremely low. More likely, all 4 sensors are simply not getting their heating power for some reason.
 

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Discussion Starter #5
So where should I go to start troubleshooting this? I'm at school and have almost no tools out here, save for a small rachet set.

JR
 

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The heater circuits are powered by the EEC. The wiring diagram I have doesn't indicate that there is a fuse or relay anywhere. The signal return also ties into the IAT sensor, so that's why I asked you if your IAT was plugged in.

I would check the engine bay fuse panel just to make sure there aren't any blown fuses. ALso make sure the connection at the EEC is solid and the pins are all clean. A wire might have been damaged, you might have to continuity check the wires to and from the heaters on the O2 sensors. I will scan my wiring diagram here in a second.
 

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Discussion Starter #7
At the risk of sounding like an idiot...where is the EEC? I'm also sure that the IAT is plugged in. I haven't touched it, and nothing that I've done would have disturbed it.

JR
 

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Discussion Starter #9
Is that information just for the Vulcan, or is it interchangable with the 'tec, as I have the 'tec.

JR
 

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Look at the diagram. On the right you have 4 separate wires going to the heating element of each sensor. They are labeled "heater ctrl" on the right side of the page as part of the pcm. These are the grounds for the circuit. If you trace through the heating element, you see that they are all spliced together and go into the red wire #31 on the left side. This is the power source for the heating elements, and your problem is likely somewhere in this wire before it is spliced into 4. Most likely the circuit is open, due to loose connection, worn wire, corrosion, etc. The problem could be right at the splice too. I have seen this happen where moisture gets into the splice and corrodes the wire. So I suppose this could be related to your mud-bogging.

So locate one of your O2 sensors, follow the solid red wire back to the splice, and look for problems.
 

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Discussion Starter #12
This sucks. Hopefully my gf's dad will be available next saturday when I'll be able to look at this problem. Until then, I'm going to have to deal with the SES light.

Thanks for your help, guys! Also, if anyone else has some input, it would be welcomed!

JR
 

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Discussion Starter #13
After speaking to a couple motorheads at work, I've decided that I'm going to try to replace the upstream O2 sensors. They said that at 80K, the O2 sensors should be replaced anyway, but that the downstream ones aren't really worth replacing at this point. When I asked about the ODBII giving the codes, they said that it was probably a malfunction in one of them, and not in all, and that the OBDII was probably just being too sensitive. So I'll order the upstream O2 sensors this week, and replaced them next weekend. I'm also going to do a write-up on how to replace them for the 'tec.

Thanks for your help.

JR
 

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they are wrong. O2 sensors don't go bad that way, and when they do they don't throw heater codes. but if you like throwing money away be my guest.
 

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Correct. When HO2S sensors go bad they start to go lean. They don't throw heater codes and they don't affect the other bank.


If you look at the wiring diagram, the returns are all parallel, so one circuit cannot affect the others.

But I DO agree that it won't hurt to replace the HO2S sensors. I just don't think that it will fix your problem.
 

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Originally posted by silvapain@Aug 6 2004, 01:21 PM
Correct. When HO2S sensors go bad they start to go lean. They don't throw heater codes and they don't affect the other bank.


If you look at the wiring diagram, the returns are all parallel, so one circuit cannot affect the others.

But I DO agree that it won't hurt to replace the HO2S sensors. I just don't think that it will fix your problem.
The returns are parallel, but the positive is a single line spliced into 4, which would mean if you had a problem there, all 4 O2 sensor heaters would go dead, and the parallel returns at the PCM would all see zero current and throw codes. I am 99% sure this is where your problem lies.

Also, if you are experiencing bad fuel mileage, and have tried other things to improve it (plugs, air filter, clean maf, injector cleaner, etc.), then it might not be a bad idea to replace O2 sensors. Otherwise though they are usually fine to 100,000 miles or more.
 

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Discussion Starter #18
OK...my plan is to replace the upstream sensors just to replace them. It's probably worth it at 80K anyway. I'm not getting poor mileage...typically an average of 23-25 mpg, which is about what I've been getting since I bought the Sable. I am going to check the wires though. I'm afraid that something might have been hanging down and gotten caught on a branch in the mud puddle then gotten ripped off. So I'm looking at this wiring diagram, and I see that the heat circuit for each O2 sensor has two wires, one of which is red. All the red wires come together to splice into one. We know that. That wire seems to be the ground, right? If the other wires, which are all multi-colored and come from the Heater Control (which I assume to be the EEC), the red must be the ground. That's what I'm going to be looking for. I don't think it could be a problem with all four positive wires coming from the EEC...I'll let you guys know what the problem was.

JR
 

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Originally posted by silvapain@Aug 6 2004, 07:28 PM
Actually, the postivie heater line to the HO2S sensors are all separate.  Look at the wiring diagram I posted.  The EEC sends out four separate heater feeds.
The 4 separate lines going to the EEC are the GROUNDS. The single red wire that splices into 4 is the positive wire, hence the red wire color. When things like these are controlled by the EEC, it is almost always switched by completing the ground, as in this case. This is done so that the EEC doesn't have to be used as a source of power for sensors, solenoids, etc.
 

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Discussion Starter #20
I did think it was kind of wierd that the ground wire would be red, but I didn't think that a ground would be sent to the EEC. In that case, I revise my earlier post, and will rather check the POSITIVE red leads.

JR
 
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