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P0138 Code

Drawnnite

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Have been having this code come up a fair bit lately.
I know it is the Drivers Side, Rear Oxy Sensor High Reading.
Engine is a 6.0L L98. Has a Catback on it.

It only seems to pop up when cruising along, Its random when it does.
Sometimes its cleared by a scantool and stays away for a bit. Other times it will come back reasonably quickly (So no consistency)

Replaced the O2 sensor initially. Still came up
Have swapped O2 sensors side to side, and it still only picks up on the RHS. Still came up.
Replaced Cats incase it was a cat starting to fail.

Am wondering where the Earth for it (purple wire?) runs, and if that runs into the Controllers in the LHS Footwell area.
Did connect up a wire for a new headunit and curious if maybe we teed into the earth or similar by mistake.
And have read that it could be a coolant temp sensor? (some other thread on here for a VE had something about that)

Wondering if anyone has any further advice in solving the problem beyond what I have tried so far.
Or if there is something else that will trigger it.
Or anything else that would be ideal to check out.
 

mechanic

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O2 sensors earth through the ECU.
Follow the diagnostic flow chart first before you go replacing everything. Could just be a high resistance electrical connector.
 

Drawnnite

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Yeah thats what i've been thinking as another likely culprit. (Electrical background).

Just seems odd as it came out the blue, and was not long after the headunit change.
Might have to go scope out a wiring diagram and see if that was the Earth wire by mistake.
 

Drawnnite

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So, should have some time on the weekend to go over it.

Plan is to remove 1 of the wiring connections from the headunit as i have a feeling that may be related (ment to be speed sensor but i havent noticed it change with speed). It goes down to the passenger footwell, which is why i am suspicious.
Otherwise....
Any recommended points of high resistance? Trying to figure out other than the plug that connects the o2 up to the wiring loom if there may be another spot or 2.
May also try find a few extension looms to connect the left and the right up to see if it follows the side or if it could be another errant issue.
 

Drawnnite

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So, can add to the fault findings.
Drove it and was going well, then the Code came up. Happened while cruising at 80 in 6th (not using cruise).

Took it to the local mech and we put a proper scan tool on it (GScan)
Is the P0138 code, but in the other format of "P2A01" if memory serves right.
Cleared it and then went in to diagnostics mode and monitored the values.
All of the other 3 O2s (Both fronts and Passenger rear) were varying from say 0 up to about 800mV and could see them changing.
Rear Drivers would not go below 740mV and would go up to about 800mV at max.
It has new Cats on both sides, so it rules out the Cats i guess.

Hopefully someone may have some other suggestions on what to look for or any other wiring suggestions to look at.
Going to clean out the plug with contact cleaner, inspect it and when reinstalling it will put some self amalgamating tape on it.

Any other suggestions would be handy.
 

Drawnnite

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Well got under it and took off the rear O2s (both sides)
Seemed the Right was still a bit black in colour which would explain sitting higher in the mV.
Maybe it was the old cats causing it.

Gave all the elec connections a clean.
Gave the O2s a clean aswell.
And swapped the one from the left onto the Right and vice versa as we knew the one that was on the LHS at the start of the day was playing nicely and had been clean, so will show up if its sooting up or not.
 

Drawnnite

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Well I am semi digging this up again to chase some more info.

Been lazy and haven't gotten the rear extensions yet to do the crossover to see if its wiring.
Am fairly certain its not (although its still on the to do list).

Have changed Plugs and Leads.
And it came up again (although could have been a coincidence?)

Still want to get it to the local mechs and plug in the G-Scan as it has the live readings. see if its still sitting high at the 700mV at idle (not going up and down)
But what else would anyone recommend?
Wondering if it could be an injector or coil pack on the RHS it the O2 sensor is still staying black which indicates fuel not being burnt?
 

Drawnnite

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So finally got the o2 loom extensions from Performance Exhaust and will do the left to right change over and hopefully get it on the mechs GScan to see the mV readings.
If it swaps to show the "left" reading solid 700mV we know its not the wiring but engine related

Probably also going to order some some Coil Packs and swap them out on the RHS.
Have noticed that there is a bit of a faint miss which also makes the idle a bit more rough then normal. (has been like this a while).

Any other suggestions appreciated.
 

Drawnnite

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So hopefully someone sees this and gets an idea to send through and assist.
(does seem to become a 1 person monologue at times)

Coil packs from side to side (all left are now on right and vice versa) still has the P0138 error.
Rear right o2 sensor is getting black so i assume fuel isnt being burnt.
Could it be the Injectors? And if so any recommendations on how best to change lefts to right?

Over the next few days will be using the loom extensions to "swap" the left to right circuits.
Would be handy to have access to the gscan to see the live readings.

Any other suggestions would be helpful.

EDIT: Has been suggested inlet manifold gaskets, so will do them aswell.
 
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Jolls

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I think you need a scan tool to read the live data. If you change one thing at a time and you should be see the corresponding result in the data stream. I forked out the beer tokens for a knock off Tech 2 and it has been worth its weight.

Find the DTC description and diagnostics attached in case you don't have it. I can only suggest following the diagnostics check list with something that can read the live data.

I trust this helps
 

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