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  #1  
Old 07-11-2021, 10:50 PM
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Oxygen sensor heater readiness monitor is incomplete

2001 3.0i, closing in on 200k miles.

Car runs great other than ...

The "oxygen sensor heater" readiness monitor is not completing (according to my Foxwell), so the car can not be smogged.

I have NO CODES, either OBD or BMW. All other readiness monitors show as ready (7) or not applicable (2). All but this one incomplete monitor reset within a day or two of the last code reset, but this last one refuses to complete, even after a couple of hundred miles over several days.

I've read up a lot on this on the tubes and the most believable answer seems to be that I do actually have an issue with one of my O2 sensors. Not enough of a problem to set a code, but enough to not let the test complete. Weird.

https://www.nyvip.org/PublicSite/OBD...r-monitor.html

https://www.bimmerfest.com/threads/s....576621/page-2

https://www.bimmerfest.com/threads/b....926859/page-2

I replaced the upstream O2 sensors with new Bosch 13477 at 170k miles when I first got the car and hoped for an improvement in mpg that did not follow. The downstream sensors (Bosch 15109) are original.

Questions:

Agree with the plan to replace the downstream O2 sensors?

Can that readiness issue be caused by upstream, downstream, or either type?

Any testing or live data analysis I can do to learn anything before making the repair?

I've seen a ton of discussion about the federal test procedure drive cycle, but no explanation for why my driving very quickly reset all monitors but this one, so am doubting at this point that further driving will guarantee completion. ???

========
Background on how I got here:

Service Engine Soon light came on, right before my bi-annual CA smog check. OBD2 P0444 code / BMW "44: DME: Activation, solenoid valve; tank ventilation" code, both pointing to a gas cap or evap purge valve.

The original purge valve ( 13-90-1-433-603 - Fuel Tank Breather Valve) tested electrically and mechanically (~28 Ohms, solenoid clicking strongly when actively tested with Foxwell, air flow confirmed to be open/blocked when doing that testing) perfectly. But I eventually ran out of other possibilities and found enough reports saying that the purge valve might bench test perfectly and still throw the code, and also that non-Genuine-BMW replacements could be similarly bad.

So I replaced with a BMW valve, reset the code, and it has been perfect other than this monitor readiness issue. No code has come back.

And now if I find similar result with the O2 sensors (test fine, but won't let readiness complete), I will not be surprised.
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Old 07-11-2021, 11:07 PM
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I had a lot of problems with o2 heaters until I replaced with OEM.

That said when I had a problem with o2 heaters I figured out of had to reset the heater calibration and to do that; two starts with both o2 (post or pre) unplugged. Then reset codes and plug back in. I've used it a few times on different cars.
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Old 07-12-2021, 03:21 PM
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Quote:
Originally Posted by andrewwynn View Post
I had a lot of problems with o2 heaters until I replaced with OEM.
I believe Bosch is the OE supplier for these. These are the current Bosch Part numbers:
Bosch 13477 pre-cat
Bosch 15109 post-cat
Bosch 15738 universal (for both pre and post-cat)

I put Bosch 13477 in the upstream locations 30k miles ago. Assuming those are still good. Downstream ones are original at almost 200k miles.

Any concerns if I replace with Bosch rather than Genuine BMW?

I called Bosch to confirm about universal vs. the application specific ones, and the sensors themselves are identical for the 3 types listed above. The only difference is in the connectors. I pointed out that the three types have 3 different photos on the website, and was told that they are the same, and the different photos are just due to evolution in how they actually make them. Specs are the same, and at any given time, the same sensors are going out with those 3 different connector types.

Quote:
Originally Posted by andrewwynn View Post
That said when I had a problem with o2 heaters I figured out of had to reset the heater calibration and to do that; two starts with both o2 (post or pre) unplugged. Then reset codes and plug back in. I've used it a few times on different cars.
I will definitely give that a try.
Unplug all four?
Two starts - is that literally start, off, start, off? Or does it need a couple of trips / drive cycles?

Also, BTW, none of the O2 sensors have been touched since 2018, so it's not like anything was messed with while I figured out the purge valve replacement.

Once I get access to the connectors, I'll do some resistance checks to see if the heaters are clearly bad. I just wish if they were bad I'd get an actual code rather than this failed readiness thing. Any other easy test ideas?

UPDATE - resistance checks on the 2x original upstream ones I removed in 2015 (saved them since they were still apparently good), and the 4x in place now gave between 2.3 and 2.7 Ohms across all 6. Was really hoping to find something out of order here.

I pulled all 4 connectors and did a little test drive. When I got back, stopped, started, idled, and then in less than a minute the SES light came on.

Foxwell then confirmed 4x codes for the Heater Control Circuit on each sensor (P0056 [3D][B2S2] , P0036 [4F][B1S2], P0050 [37][B2S1] , P0030 [19][B1S1]). E.g., first one, P0056 is the OBD2 code, 3D is the BMW code, bank 2, sensor 2.

Then re-connected things, and will see what happens.

OBD2 readiness monitors still showed 2 N/A, 7 OK, and 1 INC.

I did not reset codes, hoping they will reset themselves and any calibration will be triggered.

Let me know if I should have done anything differently, or should do something else now other than wait.
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Last edited by oldskewel; 07-12-2021 at 05:16 PM.
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Old 07-12-2021, 06:02 PM
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Oxygen sensor heater readiness monitor is incomplete

I reset codes after the heater calibration. The heaters are so low of resistance they are almost like the wire so the computer figures out the actual resistance by measuring the current.

A minor change in the resistance say at a connector or in the heater or inside the DME will cause a heater error.

The only cure I've found was outlined above.

I use Bosch on all my O2. I have zero problem using oe or oem part for any part of the car. For non mission critical parts I will use knock off. Especially wheel afford sensors which are so easy to change and are not likely to stand you. I would maybe bring a spare on a long trip.

I only idled the car and off. Did that twice. Then I cleared the codes it would prob take five hot/cold drive cycles to clear the O2 codes on their own. You can reset your emission monitors faster I would reset.

Use the obd main menu to read monitor status.
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Last edited by andrewwynn; 07-12-2021 at 06:55 PM.
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