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Tuesday, September 22, 2020

Doug's Domain

Doug Vetter, ATP/CFI

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August 4, 2004

Oil Service, discussions about tranny / diff fluid flushes, possible catalytic converter problem, and Big Brother at BMW

Just another oil service this month. What can I say...I drive the hell out of this thing. The machine also rolled over 100000 miles a week or so ago. All things considered, the car is performing well (and no surprise...it seems at times like I've replaced everything that can be replaced...knock on wood).

I've noticed a slight rubbing / pulsing vibration when turning to the right occasionally, particularly in the morning. I watched my mechanic give the front end a good inspection while the car was up on the lift for the oil service and he said everything is in good shape. I asked whether it could be bearings, and his general thought was "no" simply because these cars don't have problems with bearings as long as the dust seals don't fail. That leaves the most likely case of tires, but they looked good to both of us. They're wearing evenly.

We spoke briefly about flushing the tranny and differential fluid. Turns out the tranny uses common ATF fluid, which is pretty cheap, while the diff uses a more costly synthetic fluid. He said that when he drains tranny fluid it's usually dirty, while the diff fluid looks clear, so my general take on this is unless you're towing something (with a BMW? Yea, I know), you probably should replace the ATF fluid at every other inspection II (every 60K miles) or just do it at 120K miles as BMW recommends on some of their tranny's, and do the diff fluid every 120K miles, if that.

The tranny has a filter, but it's never changed. Automatic transmissions also have a lot of critical seals and valves that can go bad. Unfortunately, when that happens, you're looking at a new tranny. They used to quote labor to repair transmissions in the field but they simply don't do that anymore. And, with the cost of labor and related warranty support issues, who can blame them. It's very likely cheaper and easier just to replace it. Note that I didn't say cheap...I said cheapER. I was late to the appointment and in a rush that day, so I didn't want to wait for the fluids. I told him that we'd do that and a quick test drive of that front end vibration (if it persisted) at the next appointment.

Being the cool guy he is, my mechanic offered to pull the codes from the OBD (no charge) just to make sure everything was running okay, and I watched him as he did it. Turns out that the emissions control subsystem reported two occurrences (the most recent occurring roughly 15 hours ago) of "low catalytic converter efficiency" on cylinders 1-3. I'm not sure exactly how the computer determines this, but I imagine it compares the output of the oxygen sensors on either side of the cats and flags an error if they disagree. This means either one of the cats is on its way out, or maybe one of the oxygen sensors is going bad -- I don't know which.

This should only be of concern before I go for inspection in September of 2005, so I figure I'll burn that bridge when I come to it. I don't know whether I'll even have the car by then (hey, anything can happen), and if it continues to be a rare, intermittent issue that doesn't detrimentally affect performance, I can always make a quick stop by the shop to clear the codes before I go to the DMV. After all, I don't know whether the DMV's computer will flag a single occurrence of this condition as a "major fault". The car's own computer doesn't seem to think it's that big a deal, because it didn't flag the check engine light (and it will only do this if the number of faults exceeds a given threshold). And I'll be damned if I'm going to drop probably almost 2G's with labor just to appease this EcoNazi state.

I also mentioned that I once noticed when in manual mode (A/M switch in "M" position), the shift from 1st to 2nd took a bit longer than I remember. My mechanic and I then discussed the shift adaptation program -- the tranny learns how you drive and adapts the length of the shift to suit that driving style. This means if you drive casually, it will shift smoothly (i.e. take longer to shift), while if you punch it all the time and depress the downshift trigger frequently, it will tend to shift more quickly, and thus more abruptly. He offered to clear the adaptation memory so the tranny would start learning from that point on. I tried to duplicate the condition again after I left the shop, but was unable to do so. I don't know if clearing the memory had any effect, but it was kinda cool to see him use the diagnostic computer to do that.

One interesting thing I learned about the diagnostic computers that BMW dealers use to analyze faults is that they're linked to BMW headquarters. When your car goes in for service the computer dumps the entire memory (not just the parameters the dealer can see or change) and sends it to BMW for analysis. This allows them to track faults and issue service bulletins for "hot" items. Yea, it's a bit "big brother", but that's technology for ya.

Parts $37, Labor, $38, Total $88. Mileage: 100984.