Removed cats and reinstalled O2's now code 28 (1 Viewer)

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So like my post title indicates, I recently bought another FJ62 and in getting it baselined, changing all the fluids, plugs, brakes, knuckles etc.. I brought it up to my local exhaust shop who has a great rep.
I instructed them to remove the old cats which had holes and to re mount the old O2 sensors, one of which had a hole at the mounting location. They did the job... then to realize the muffler has a huge hole where it couldnt be see... but anyways..
Driving home I notice the check engine light on(this is how every exhaust repair thread starts that i have read). Shut it off at home and try to see if turning off and on makes the light go out. It didnt. I then pulled the EFI fuse for a couple minutes or so. Light is still on. Then today I got a few minutes and read the codes. I have 28 and 51.
I do believe 28 is the #2 O2 sensor. Question to you fine folks is..(because after reading almost every O2 sensor thread I have no clear answer.) since the OEM sensors are NLA(I called to double check) what is everyone using as a replacement. Did you have to splice them in, and were they also 4 wire or what? Can someone please supply me with a part # of what to go get. I'm not afraid of splicing one in so long as I know which wires to connect(worried about going from 4 wires to 2 or 1)
Should I do anything before jumping to replace them. Maybe a good wire jiggling is in order... haha just kidding but not really. There were no codes present before the exhaust was repaired. well maybe 51 but was not indicated by the check engine light.
Please, any part #'s or tips would be appreciated. Some of the O2 sensor threads are really old and some of those O2 sensors I looked up dont seem to exist any more.
 

60Works

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You can buy O2 sensors direct from Denso which have the correct plug.
 

cruisermatt

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Check the O2 sensor wiring where it goes up the back of the motor. The wiring for one goes near the exhaust manifold and can get burned up. Otherwise try throwing a pair of new sensors in.
 
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Thanks guys. I'll give the plugs another look. The one easily seen from the engine bay down by the drivers rocker panel is looking good. I was able to feel the plug for the inboard side and it didnt feel burned, but hard to tell. I will check again then replace if needed.
 
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Code 51 does not look related to the exhuast snafu.
1955332


I'm going to go with O2 sensor wires were not installed correctly or exhaust shop pulled the wires out of connector giving you a short. This short would give you code 28/21.

1955333

1955334
 
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You removed the cats or replaced the cats?
Because you only said “remove”

If there is no cat between the first and second sensor then the sensors think the cat isn’t doing it’s job, hence a CEL.
 
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No "downstream" sensor on an 80's vehicle to monitor cat performance. There are two upstream sensors on the 62 - Bank 1 and Bank 2. They don't know if there are cats there or not.
 
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Thanks for clarifying that, Prairie Swamp for mr Red. I did my homework on removing the cats(I was never good at homework though)
I have a couple FSM's so will grab one and try the continuity test. However, im not good at electrical testing, so will have to grab one of the electrical engineers at work to lend a hand.
Randy, as always, you Da Man. Always quick to lend your knowledge and I appreciate that! You were definitely one of the pros I was hoping would chime in.
All else fails, will bite the bullet and spend the $80 on new O2's
 
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Per Matt and Randy's suggestion - have your buddy help you check the wiring from the ECU to the O2 sensor connector (HT1 and HT2). If you are getting a code for "short circuit" you can unplug the O2 sensors completely, clear codes and see if it comes back. If the "short circuit" code comes back with the sensors unplugged it's likely in the wiring. Possibly where Matt describes. Yanking on wires during exhaust work may have also caused a short.
 
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Thanks. I will do as you recommend. In checking out the wires and connectors, all looked okay and there was enough slack that they should not have had to yank on the O2 sensors to get them back in place at all. I cannot say that the wires are clean on top of the transmission, but I could see the connector and that looked good from the sensor to the connector. Could be a burn or pinched wires up further for all I know. The curb side sensor wires can be seen easily from the engine bay all the way down to the plug and beyond. Those look fine and still have the plastic/rubber sleeve/wire loom.
If I understand what you are saying, the truck should not throw a code without the sensors plugged in at all(ie. removed completely) from the harness. If it does throw a code, there is a short before the 4 pin plug that the sensors plug into.
Would it make sense that if the light goes out without the sensors, I could just leave them out altogether or unplugged indefinitely(would need to plug bung holes if removed)
Is there a down side to this?
 
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Without O2 sensors it will run like crap. The ECU will go into a programmed air fuel mixture mode instead of giving the correct air to fuel mixture. You want to fix this, not ignore it.
 
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Your absolutely right I want to fix this. Issues like this drive me crazy until remedied. Thanks for all your input. I'll be sure to post the final results. To be quite honest, I am hoping the repair is to just replace the sensors. New sensors, peace of mind.
 

cruisermatt

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Actually I couldn't tell a noticeable difference in engine behavior with burned up O2 sensor wiring, I did have the same CEL light though, in my case it would only come during long highway trips though. My suggestion on burned up wiring near the exhaust manifold was one from experience by the way.
 
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Okay, time to put this one to bed! I bought new sensors and installed them(Denso 234-4056) , which was easier than I had expected. The hardest part is getting the sensors unplugged up there. Luckily the bungs are new and easy to remove the old sensors.
Next I removed the EFI fuse for a couple minutes, put it back in and started the wagon. Check engine light came on at ignition and then right out as planned when she fired up.... Then I immediately smiled with relief.
You got to love a straight forward part replacement to solve an issue.
Thanks again to all my imaginary friends(as my wife would say). Your better than real friends!!!
Now on to other fixes, upgrades and repairs
 

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