After three years of planned non-operation (storage) we decided to wake up our 92 525i (automatic) for my son. With a new battery, she started right up, so we activated the registration and were instructed to have the car smog checked at a Star Station. We changed the oil, oil filter and air filter, took it for enough of a run to heat up the cats and took it to be tested. Not surprisingly, it failed, but just barely for HC. NOX was high, but within passing.

2nd try: after new plugs, valve cover gasket, and running a tank of fuel with fuel injector cleaner, I refilled with regular unleaded fuel, took it for another good run, and it failed again--worse. Higher on HC and higher, but still barely passing on NOX.

3rd try: I had my cats inspected by the shop who installed them just a couple years before we quit driving it. They cut inspection holes on both ends of both cats and said that visually, they look to be in perfect condition, and although that did not definitively mean they hadn't failed, they believed they were most likely good. I then tested my 02 sensor, which put out voltage within the specified range, but did not fluctuate as it should. Believing this to be the problem, I changed the sensor, ran the car, and returned to the test station. It failed again!! Now it failed miserably on HC and was over the limit on NOX as well.

Now what?

No fault codes, no Check Engine light

Also, the MAF fails the diagnostic test where it should read 5v and the hot wire glow red for about 1 sec, five seconds after revving the engine past 2500 rpm and then turning off--There is a click at the right time, and about .4 volts, but not enough to heat the wire. A send unit from the junkyard performed exactly the same way...Where does the 5v come from? Could this and the rock solid reading I got from my 02 sensor indicate a failed DME module?

If these results suggest anything meaningful to you, please share your thoughts.


92 525i
95 540i M-Sport
2001 740iL