Matthew So

Hi all,

I have been looking for info about generic O2 sensor for post-95 993. I saw that Bosch 15738 was mentioned as the generic replacement but does it work for both the pre/post CAT? I know they are different in color in OEM form (black/gray) so not sure if Bosch 15738 can be used in all 4 location. Thanks!

Regards,
Matthew

71-3.0-911

I used them post cat and ran them with no problems for years. Then I used another generic Bosch set that were listed as pre-cat and after 100 or so miles started getting O2 sensor errors. So, I replaced them all with specific OEM replacements and not an issue since.

So, I think post cat, you can get away with it. All 4, my experience says it's suspect.

-Scott

pp000830

Hi Matthew,
A BOSCH branded oxygen sensor purchased online or through an import parts distributor is identical to the Porsche branded part being made on the same production line.
The only thing it is missing is the Higher dealer markup, It can be purchase from pelicanparts.com or it may be less expensive at Rockauto.com.
I would not buy one of their universal replacement ones with the raw wire pigtail. I would get the one made for our cars with the correct wiring harness plug.
May I ask what prompts you to replace the sensor?
.
At the bottom of this page is instructions to make it easy to replace a sensor with the back of the car on jack stands:
https://993servicerepair.blogspot.co...anagement.html
.
Here is a page that discusses lifting a 993 for servicing:
https://993servicerepair.blogspot.co...-your-993.html

Replacing an oxygen sensor is one of the easier DIY projects. Be aware the before Catalytic converter and after ones have different part numbers and the wiring harness sockets in the engine compartment are color-coded gray or black so the sensor plug is inserted in the matching color socket.
Andy

geolab

I am sorry, this is not true at all. I personally think this it is totally made up, you cannot say things like that !


You are giving your opinion advice, without answering the OP's question , hello ?
Andy, what is happening ?

geolab

Hello Matthew
ALL o2 sensors are the same on the 993, what differs is the lenght of the electric connection cables, thus they differentiated the electric connection plugs and color of plugs, and part numbers

Bosch 15738 is the generic replacement AND IT DOES work for both the pre/upstream and post/downstream , and surely can be used

Bill Verburg

The thing to be aware of is that reference air for the O sensor is drawn through the electric pigtail sheath, I would make sure that what ever O sensor you use allows for that

Matthew So

Hi all, thanks for the advises.
The reason I am thinking of changing my O2 sensors is because I am getting more frequent P0300 code and it always comes with P0304,P0305 and P0306.
It happens when the car is warmed up. It could happen anytime after I drove the car for 30, 50 or even more miles. It does not happen when the car is cold.
Starting up is never an issue, and there is no loss of power. Acceleration is perfectly fine too.

Since the codes all comes at the same time when I have CEL, it leads me to think that it has something to do with components that are affecting my right hand side of the engine only.
I have checked my records, and it shows that my ignition wires, distributor cap and rotor were replaced 20k ago. I can check to see if there's any leak/arc at dark but I doubt these components are the reason for the misfire.
I personally replaced alternator, fan and A/C belts using Porsche OEM parts less than 2k ago. I did update the pulley plate but then I also checked with tension gauge and it seems to be within spec.
The only three things I can think of that would be the reasons are:
1) O2 sensors
2) Distributor belt
3) Dual Coil pack

I checked my record and see that there is no record of O2 replacement since 2017, so this will be the 1st thing I will do. At the mean time I will try to check and see if my distributor belts are running ok.
I tend to think the dual coil pack should be the most reliable components out of all the one I mentioned above, but feel free to correct me if that's not the case

For now I am ruling out vacuum leak and Dual Mass Flywheel because the misfire code is always P0300 follows by P0304, P0305 and P0306 every times I have CEL. But then again if my assumption is incorrect please feel free to correct me.
BTW, the previous owner did not replace any spark plug when he replaced the ignition wires ( ) so I plan to also update my plugs while trying to figure out the root cause of misfire issue. I was told it's a 9 hours job....oh well...

Regards,
Matthew

pp000830

Hi geolab,,
I have to respectfully disagree.
I have purchased both Porsche branded and BOSCH branded, they are identical even to the point of both having the Porsche part number etched onto the sensor barrel. BOSCH makes both.
I do not recommend using the sensor with the raw wires because of reliability issues associated with splicing the pigtail.
It is true I did not explore this reasoning in my original posting.
As you note they are not interchangeable due to wire lengths, I was unaware that they have identical electronic properties.
Andy

pp000830

Hi Matthew,
I would add to this by verifying that the ignition wires are routed correctly to the proper cylinders.
Testing both the direct drive and the belt-driven distributors is discussed on this page.
https://993servicerepair.blogspot.co...ling-dual.html
It might make sense to do this test when the engine is hot and the codes are present in case the root cause is heat related, for example, an ignition coil that cuts out when warm.
Also, don't discount something very simple like a slightly loose distributor cap. I have had this experience triggering misfire codes.
Andy

71-3.0-911

This is not my experience. The actual sensor that is in the exhaust stream is different. The Porsche branded specific ones have a more bulb shaped sensor tip where the generics are more cylindrical with some holes in the tip.

My car may be more sensitive but running 4 of the generic sensors caused multiple O2 sensor codes, with regularity. Once I replaced all 4 with OEM specific sensors, this all went away.

Again, correlation is not causation. YMMV.

-Scott

Matthew So

Thanks for your input Scott. At least post-cat is ok with generic Bosch one, right?
Unfortunately I cannot find any seller online with a picture of O2 sensor that looks like what you described as the OEM version (cylinder with many holes). Bosch 13662 does show up as alternative for Bosch 13721 but the connector is very different.
Anyone else have any story with generic O2 sensor vs OEM?
Thanks!

Matthew

71-3.0-911

Bosch universal and specific. Specific has closed end where universal has small holes in the tip. If you look closely you can see them. Sensing element is clearly different.

Matthew So

I also notice the different between the universal one and Bosch 13721. It is the OEM Porsche one that Scott mention is very different, that's why I mentioned 13662.
So 71-3.0-911 have you tried using Bosch 13721 and 13723 (pre/post CAT) and do you find them to be trouble-free?

Matthew

71-3.0-911

Honestly, there may be some mash up of universal ones that work. In my car, it simply didn't. If you want a guarantee and to not have to mess with it again, I'd spring for the OEM specific ones from Bosch.

SwayBar

Just buy the slighty more expensive OEM O2 sensors - it's not like it's a $5,000 part.

8 years ago my OBD codes stated specifically both left-side sensors were bad. I replaced them with the slightly more expensive OEM ones. Their wires were the exact length as the original ones - and I've never had a problem since.

I've learned a while back, in the long run, one saves both time and money buying OEM parts vs the cheaper-priced ones.

Of course there are exceptions where a part is not marked as OEM, but is the OEM manufacturer in a different box - for example, the ignition switch. You can do that successfully, but takes additional footwork to recognize. But when in doubt, buy the marked OEM one.