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Downstream O2 question

 
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Old 27 Feb 2017, 02:47 pm
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Default Downstream O2 question

New to the PT here. I got the trouble code 140 and 139 so crawled under the car with my o2 sensor wrench to investigate and the downstream sensor isn't plugged in at all. The pig tail on the sensor is there and looks to be the round type like the upstream one, it's just not plugged into the cars harness to the pcm.My question to the forum is where is the harness plug most likely to be at? Would it be in the same group the upstream sensor is? Or is it in another place entirely? I've searched the car for an hour or so and the factory manual and still am lost. Also I'm pretty sure this car has an aftermarket cat b/c the sensor is in the side of the cat instead of after. Any clues would be appreciated and thanks in advance.
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Old 27 Feb 2017, 02:58 pm
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Default Re: Downstream O2 question

I believe the rear oxygen sensor wires come down from the driver's side down right behind the steering sector. I'm at work so I can't take a photo.
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Old 27 Feb 2017, 03:15 pm
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Default Re: Downstream O2 question

Quote:
Originally Posted by Jthawk71 View Post
New to the PT here. I got the trouble code 140 and 139 so crawled under the car with my o2 sensor wrench to investigate and the downstream sensor isn't plugged in at all. The pig tail on the sensor is there and looks to be the round type like the upstream one, it's just not plugged into the cars harness to the pcm.My question to the forum is where is the harness plug most likely to be at? Would it be in the same group the upstream sensor is? Or is it in another place entirely? I've searched the car for an hour or so and the factory manual and still am lost. Also I'm pretty sure this car has an aftermarket cat b/c the sensor is in the side of the cat instead of after. Any clues would be appreciated and thanks in advance.
Welcome to the forum.

What year is your PT Cruiser?

I would suggest looking at the chassis next to the location of the 02 sensor. The harness plug might be tied down where you can't see it until you are on top of it.
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Last edited by ptcruisersteve; 27 Feb 2017 at 03:18 pm.
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Old 27 Feb 2017, 03:21 pm
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Default Re: Downstream O2 question

Oops sorry it's an n/a 02 touring
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Old 27 Feb 2017, 06:08 pm
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Default Re: Downstream O2 question

I found it coiled up under the air cleaner for some reason. I reconnected it and now the asd fuse keeps blowing.
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Old 27 Feb 2017, 09:15 pm
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Default Re: Downstream O2 question

You might have a short to ground causing the alternator to output more and tends to blow the ASD fuse. The O2 sensor heater circuit that is on the ASD fuse might be the short causing the generator (alternator) to work harder to compensate for the short increasing the voltage to a very high voltage and when the current is too high it blows the ASD fuse. Check your 02 sensor.

I would also check the wiring harness coming from the camshaft and crankshaft sensors going to the PCM. The 2001 & 2002 is popular for the wire harness clip holding up the harness to break and start rubbing on the axle or frame eventually shorting wires out.
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Last edited by ptcruisersteve; 28 Feb 2017 at 12:01 am.
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Old 01 Mar 2017, 01:35 am
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Default Re: Downstream O2 question

Thanks I'll check those things too, I ordered a new o2 sensor. When I plugged it in it wasn't showing any voltage change like the other one does on my scanner so I figure it's bad and that's why the po had it unplugged.If it was just idling it wouldn't blow the asd fuse but once I put in gear and gave it a little gas it would blow the fuse. I did a search on this forum and I'm not the first guy with this exact problem. I'm going to keep a handful of fuses in the glovebox from now on. Thanks everyone for the help. This is a very helpful forum.
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Old 01 Mar 2017, 02:48 am
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Default Re: Downstream O2 question

Let us know if the new 02 sensor fixes your issue.
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