short in o2 sensor signal circuit - p0138

[nugentc]

I didn't know whether to post this here because it was electrical or to Maintenance Bay.

I have a 2006 Pontiac Vibe with 132,000 miles. I recently got CEL codes p0136 and p0138 so I changed the rear oxygen sensor. CEL was still on afterward and I didn't know I needed to manually clear the codes, so I went to have them read--still p0136, 0138, but then p2195 in addition. Then I learned I had to clear the codes myself.

After I did this, within a day, CEL came back on and p0138 is the only current code. I have checked the 3 fuses for EFI under the hood but don't know what else to check. Apparently this code error is related to a short to battery voltage in the 02 sensor circuit.

Any ideas about how to find and fix my problem?

[M1MECHANIC]

when you reset the code you disconnected the neg. battery terminal for 30 sec., then reattached it correct? If so you may need to do it again and make sure you put the neg terminal on in a quick motion. If you do it to slow and the terminal is really loose you can get a slight surge the will cause it to fault out on the same fault again. You want the terminal to come off with a little resistance so when you put it back on there is no room or slight arching as you put it back on. Hope this helps.

[kumquat]

Looks like your first order of business is to check the actual voltage on the heater circuit at the sensor.

Pin 3 looking into the female connector is ground.The one above that (black) is the feed circuit. Top left (pink/black) and bottom left (white) are heater control.

[nugentc]

M1MECHANIC, this is interesting. Yes, I disconnected the battery terminal to reset the code. It was loose and I did notice some arcing. I'll try it again with it not so loose.

kumquat, I'm without my multimeter, but the people at Autozone supposedly read the voltage from the code reader itself. Here were the readings I copied down:

O2S12: .055
O2S11: ranged from 3.2 to 3.5 and perhaps a little higher at times

The O2S12 readings seems off, right? Isn't it low?

[kumquat]

M1MECHANIC, this is interesting. Yes, I disconnected the battery terminal to reset the code. It was loose and I did notice some arcing. I'll try it again with it not so loose.

kumquat, I'm without my multimeter, but the people at Autozone supposedly read the voltage from the code reader itself. Here were the readings I copied down:

O2S12: .055
O2S11: ranged from 3.2 to 3.5 and perhaps a little higher at times

The O2S12 readings seems off, right? Isn't it low?

It says the DTC is set when the average HO2S 2 voltage is more than 590 mV for more than 30 seconds.

The voltage on the connector should be 55 mV (0.055 V)on a cold sensor with the ignition on and engine off. That seems like it's what you're getting. What about with the engine running?

[nugentc]

I thought he turned the engine on after he plugged in the code reader, but I could be wrong. I'd have to go back again tonight and have him read it again both ways. Sure wish I had my multimeter.

[nugentc]

M1MECHANIC, I tried your strategy of clearing the code and reattaching the battery terminal with more resistance. The CEL came back on this morning after driving a while. This weekend I can go back to Autozone and see if the guy will read the voltage again with engine cold and engine running. Otherwise, are there other things I can check? Something I read said it could be an exhaust leak. Since p0138 is Sensor 2, would a leak have to be before it but after Sensor 1, or could it be before Sensor 1, like at the intake manifold?

Thanks the ideas.

[nugentc]

I just found this and thought since at one time I had p0138 and p2195 together, it might apply:

http://ww.w.autoelectricpro.com/purchas ... 109156.pdf" onclick="window.open(this.href);return false;

When you scroll down in the document it says, "If both DTC P0138 and P2195 are set, replace the HO
2S Sensor 1"

What do you think?

[kumquat]

M1MECHANIC, I tried your strategy of clearing the code and reattaching the battery terminal with more resistance. The CEL came back on this morning after driving a while. This weekend I can go back to Autozone and see if the guy will read the voltage again with engine cold and engine running. Otherwise, are there other things I can check? Something I read said it could be an exhaust leak. Since p0138 is Sensor 2, would a leak have to be before it but after Sensor 1, or could it be before Sensor 1, like at the intake manifold?

Thanks the ideas.

Looking at the service manual flow chart, the culprits are either the PCM, sensor, or a wiring fault. So you really need to see what the voltage is doing with the car on and off.

There is however a TSB about p0138 and/or P0607. Looks like A/C evaporator drainage can infiltrate some wires by the footwell and possibly cause one or both. To check it out, remove the driver's right side footwell cover. There's a connector (looks like a gray plug with red, yellow, and other wires going into it) down there just where the carpet meets the console plastic. Check it for corrosion and/or moisture. Check the rest of the area too.

[nugentc]

Thanks, kumquat.

When I changed the rear 02 sensor, I didn't notice any moisture or corrosion around the connector, but I will check again.

Okay, so when I go back to have the voltage read, what will I learn in the two scenarios? I'm pretty sure the car was running when I got the numbers I posted above. If it was, what does that mean? If it wasn't, you said those looked good. So when it's running, what numbers are good/bad, and what does that mean for the next step? I want to be able to take care of any parts right there while I'm having the reading done.

Thanks again!

[nugentc]

I just wanted to post an update and some follow-up for anyone else struggling with the same issue. I checked the evaporator drain tube and it's actually not located anywhere near the o2 sensor connector in my Vibe. I might have read somewhere else that the TSB related to that is for AWD. I also checked for exhaust leaks and vacuum hose leaks. I went to have the codes read again and was getting the p0138 AND p2195 again.

There were many online forums (e.g., http://www.customtacos.com/forum/showth ... p?t=155334" onclick="window.open(this.href);return false;) and several other sources (e.g., http://www.justanswer.com/toyota/7iuv4- ... p2195.html" onclick="window.open(this.href);return false; and http://ww.w.autoelectricpro.com/purchas ... 109156.pdf" onclick="window.open(this.href);return false;) indicating that this combination of codes is due to a faulty O2 sensor 1.

So I changed that out on Saturday, have driven it quite a bit since then, and the light has not returned. Like another poster on genvibe, one of the bolts on the heat shield sheared off due to rust when I was trying to get to it to change it, but the other three seem to be holding it on well enough. Those bottom two were rusted on there pretty bad.

I hope this is helpful to someone else!

[Salsa Guy]

Thanks for the follow up. Good Info