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Double D
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148 Posts
Discussion Starter · #1 ·
Hey guys, my SEL illuminated a few weeks ago. Used my Peake tool to see what kind of codes were present and came up blank!? Have checked for vacuum leaks, none that I could find, albeit not the end all. I have new spark plugs, new coil packs, cleanded MAF, checked vacuum hoses for any possisble issues...ETC. I replaced the pre oxygen sensors about a year ago,threw a code, but I did not replace post sensors. They only had one in stock at the time, and so I replaced pre with intent to replace post at at later date. Have not read anywhere if doing so will throw SEL, without registering a code. I am aware that Peake does not have the capability to read ALL codes...Unfortunately, I have to smog for registration by mid month and if I can't get it fixed, the Stealership is my only option. Read the post about trouble shooting smog pump, check valve, et. al..will also give it a try and just maybe...Thanks in advance!
 

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The post-cat sensors can set a cat efficiency code, if they are defective. The code will also be set when the cat is actually malfunctioning.

Look in the Peake manual for the cat efficiency code. BMW code 233 (cyl 1-3) and 234 (cyl 4-6).
 

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Double D
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148 Posts
Discussion Starter · #3 ·
edjack, when I connect the Peake, it does not show a code! The car runs smooth, has power, doesn't hesitate when I take off from a stand still, can't hear anything odd in the engine bay...it's very frustrating!! I will say this though, I forgot to mention, the SEL did turn off for about three days before showing its ugly self again! Still NO code though! And I believe it's an automatic FAIL if the SEL is illuminated?? Do you think it would be cost effective to have the smog place look into it vs the Stealership?? I would think not, but since that's what they do, then just maybe??? What a headache!
 

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If it is your O2 sensor malfunctioning, the Peake should be able read that. The Peake cannot read tranny codes and the like. It should read engine codes, in particular, anything to do with emissions. Hence, it is not likely the cause of your SEL is your O2 sensor. Even though the Peake is not reading your specific code, have you tried using the Peake to reset ane clear the OBC? Worth a try.
 

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Even though I think the Peake should be able to read post-cat O2 sensor error code, it may help going to AutoZone / AAP and check it with their scanner to be sure.

The post-cat O2 sensor is not part of the closed-loop control and will not affect the fuel&ignition system. If you live in a place that does not bother about emissions, you can might as well cut the wires to that sensor.

Can you still pass the emissions check in Cali with a exhaust gas sniffer if the post-cat sensors are bad?
 

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Double D
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148 Posts
Discussion Starter · #9 ·
I've reset the OBC using the Peake to no avail! At this point, it leaves me no other option, Stealership it is. Haven't found an Indy to my satisfaction in the surrounding area. Took my vehicle to different Indy shops within said parameters when I first purchased. But the cost drove me to work on it myself! As we are all aware, saves a heap of wooden nickels as a DIY'er! Guess I will have to pay the man so I can hopefully fix it myself. Thanks again to all!
 

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Slip slidin around town
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1,359 Posts
I had a p0420 on my 540, said bank one. I swapped the left and right pre cat sensors to see if the code switched banks, it didnt. I replaced the pass side post o2 and the code left for a few days. Now its back, p0420, bank 1. its irritating!!
 

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Freude am Fahren
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6,378 Posts
My understanding is that the post cat O2 sensor does not play any role in engine function and does not need to be replaced. Hence, it should play no role in passing or failing inspection.
It tests function of the catalytic converters, so the code they will throw is a cat inefficiency code***8212;you'll fail. Expensively.
nline6 said:
I had a p0420 on my 540, said bank one. I swapped the left and right pre cat sensors to see if the code switched banks, it didnt. I replaced the pass side post o2 and the code left for a few days. Now its back, p0420, bank 1. its irritating!!
Replace the cat and report back.
 

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I've reset the OBC using the Peake to no avail! At this point, it leaves me no other option, Stealership it is. Haven't found an Indy to my satisfaction in the surrounding area. Took my vehicle to different Indy shops within said parameters when I first purchased. But the cost drove me to work on it myself! As we are all aware, saves a heap of wooden nickels as a DIY'er! Guess I will have to pay the man so I can hopefully fix it myself. Thanks again to all!
Or you can consider installing an O2 simulator for the rear O2 sensor like I did. That will get rid of that pesky warning light!
 

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Seek to understand,^Value
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25,199 Posts
it may help going to AutoZone / AAP and check it with their scanner to be sure
Just for a more complete and comprehensive answer ... the OP apparently is in California which is one of two states where it's illegal for Autozone (and the like) to allow use of their scanners!
- Where it's illegal for auto parts stores to lend you an OBDII scanner for free (California, Hawaii) (1) (2)

The OP 'can' get a free scan in California, just not from auto-parts stores:
- In California, what establishment do you use to read OBDII codes for free?
 

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Seek to understand,^Value
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25,199 Posts
Haven't found an Indy to my satisfaction in the surrounding area.
Maybe this reference from the bestlinks will help find a good indy nearby?

- BMWfans phantom diagrams (1) & realoem nominal prices by part number (1) & EACTuning prices by part number (1) labor rates by zip code (1) (2) (3) where to find a good mechanic (1) (2) joining BMWCCA (1) (2) & finding a reputable BMW indy in your area (1) (2) & the most often recommended parts suppliers (1)
 

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Double D
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148 Posts
Discussion Starter · #16 ·
I called up a smog place yesterday and got a quote of $90 to have them run a diagnostic check on my vehicle. After talking to the Tech he mentioned that it may be the transmission speed sensor?? Can't exactly recall how he expalined it, but somehow it is tied into the emissions loop, or another and that will illuminate the SEL. Anyone heard of the likes? Thanks!
 
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