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Downstream O2 sensors do need replacing from time to time. In general they usually last twice as long as the upstream. We've also been forced to replace downstream sensors at times....when readiness monitors wouldn't set and everything else was 100%.

I completely agree that you need good trouble codes to go forward intelligently.
 

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BTW - Bosch O2 sensors have a date code stamped in the black plastic connector...at least mine did.
Describe this code please. I just looked at the O2 Sensors I removed from my 2002 (at 137,8000 miles) and there is a large U and a 1 stamped on it. What does that translate to? Thanks.
 

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On one side (near the top) of the black elec connector of a Bosch O2 aftermarket sensor (While Bosch is OE for BMW O2 sensors, not sure date code appears on OE sensors) the date code is shown. It is the typical round plastic stamp with the year stamped in the center and month noted on the perimeter. It is quite small - smaller than the diameter of a AAA battery. I use a magnifying glass to read it. You could also take a picture with your phone and blow it up. I will try to add a photo later.


906528
 

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And you don’t need to replace the downstream ones


That is not automatically true. There are lots of reasons to replace, or need to replace the post-CAT sensors, but he needs to give the codes before the call can be made that he needs them or not. You're partly right, the odds of needing the downstream sensors is low, but the odds are not non-existent.
 

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That is not automatically true. There are lots of reasons to replace, or need to replace the post-CAT sensors, but he needs to give the codes before the call can be made that he needs them or not. You're partly right, the odds of needing the downstream sensors is low, but the odds are not non-existent.
I can defer to sound advice like that!
 

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On one side (near the top) of the black elec connector of a Bosch O2 aftermarket sensor (While Bosch is OE for BMW O2 sensors, not sure date code appears on OE sensors) the date code is shown. It is the typical round plastic stamp with the year stamped in the center and month noted on the perimeter. It is quite small - smaller than the diameter of a AAA battery. I use a magnifying glass to read it. You could also take a picture with your phone and blow it up. I will try to add a photo later.


View attachment 906528
That's just the date code for the connector mold production. OE Bosch sensors do have a date code but it is a laser mark on the sensor body and not in a standard format. I vaguely recall it was a Julian date code but I haven't worked for Bosch for about 10 years. I was O2 sensor development both in SC and Rutesheim DE.
 

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That's just the date code for the connector mold production. OE Bosch sensors do have a date code but it is a laser mark on the sensor body and not in a standard format. I vaguely recall it was a Julian date code but I haven't worked for Bosch for about 10 years. I was O2 sensor development both in SC and Rutesheim DE.
That's a fair point, and worth noting, but given production volumes, how likely is the connector date to be more than a year off from the sensor date? The fact that you can check the connector date (and approximate O2 sensor date) in 10 seconds without removing the O2 sensor is worth something.

A few days ago, I did find a chart showing Bosch dates codes printed on the sensor here:

I checked the sensor pictured above and it appeared to have a late 2016 date code (658), but this number was in front of several other numbers and it wasn't clear (to me anyway) that this was a date code.
 

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That's a fair point, and worth noting, but given production volumes, how likely is the connector date to be more than a year off from the sensor date? The fact that you can check the connector date (and approximate O2 sensor date) in 10 seconds without removing the O2 sensor is worth something.

A few days ago, I did find a chart showing Bosch dates codes printed on the sensor here:

I checked the sensor pictured above and it appeared to have a late 2016 date code (658), but this number was in front of several other numbers and it wasn't clear (to me anyway) that this was a date code.
If you have a picture of it, I might remember it when I see it.
 
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