My 2004 BMW 325xi has been sporting an intermittent Service Engine Soon light for almost two years. North Carolina law requires no active faults in order to renew one’s annual registration. Last year, the renewal was easy enough to manage, since the light would come and go seemingly at random. This year was trickier, because the light has spent more time on than off, but I was able to get lucky and catch it off long enough to get it to pass. I knew that next year was going to be a problem, so I started troubleshooting.
There were two codes, one related to temperature and the other a lean fuel condition. The temperature could have been a thermostat/housing combination, a secondary thermostat, or a temperature sensor. The lean fuel condition could be one of four oxygen sensors, the fuel filter, the fuel pump, the mass air flow meter, the injectors, or a vacuum leak.
I started with the lean fuel condition. A new fuel filter didn’t fix it. Not that I expected it to, but it was the cheapest option and past time to be replaced. Then I threw a set of oxygen sensors on it. No joy there either. Then I took it to the shop to have the professionals look at it. They claimed that one of the year old oxygen sensors had failed. I knew they were wrong, but agreed to have them replace it. Of course the light popped again. They couldn’t find anything obvious, so they started concentrating on the temperature problem.
The thermostat housing was the first attempt to fix it, but the light popped again. The shop then said that the temperature sensor was also bad. I balked at the $600 they wanted for that, but they’d been unable to find anything else wrong that was causing the lean fuel code. They said that it could be a vacuum leak that couldn’t be easily found but would be found and corrected by the removal of the intake necessary to replace the sensor. So, I approved the work.
The fucking light is back on, less than a hundred miles after leaving the shop. I wonder what they’ll tell me this time. Whatever it is, I probably won’t fix it. Because that won’t be the problem either, and at some point I have to draw the line. This will probably be my last year of driving this car.
While all this was going on, my 2003 F-250 decided to toast its injector control pressure sensor, making it idle erratically and cut off without provocation. Said sensor is on order, and once replaced, the car will go back in for one more round of diagnostics.
UPDATE: As of 01 December 2018, my county will no longer require the OBD test in order to renew the vehicle. If I had only known before spending all this money. It’s not like the car is suffering any performance issues.