Figuring out what that warning light means

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Okay, it wasn’t that bad.

Our E46-chassis BMW M3 broadcast a different error message: SERVICE ENGINE SOON.

Okay, what does that mean? And how soon is soon?

So we consulted ye olde owner’s manual, an oft-ignored tome handed down from generation to generation.

It proclaimed thusly:

If the indicator lamp comes on either continuously or intermittently, this …

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Wait, so you're saying that the "check engine" light doesn't mean I need to check if the engine is still there?

In 1996, we got a then-new BMW 318ti for a long-term project car. It was our first OBD II project car, and we were going to turn it into a BMW CCA race car.

OBD II meant the death of performance, people said. 

Fast forward to today, and OBD II allow me to quickly diagnose a problem. 

Want to know what's wrong with the car? Ask the car. It's amazing how much people resist that. Code readers are so cheap and simple these days, there's no excuse not to have one handy. For years, I carried an OBD-II wireless dongle in my bag just in case, it came in quite handy.

I would recommend, however, that you consult a factory manual after pulling a code. There's usually a lot more information than the generic code definition. On a Mazda, for example, the factory manual gives you a whole troubleshooting process to work through along with a list of every thing that could cause the code.

Yup. Question/answer.

I'd say the biggest obstacle here was hitting every red light while heading to JG's to grab the code reader. 

Guess I should return it, too....

In reply to Keith Tanner :

And if you don't have access to the actual factory manual, I've found that the $20/month alldatadiy subscription for a given car will give you that as well.  Those troubleshooting flowcharts are fantastic for making sure that all the right stuff is getting ruled out.  They'll usually have test processes and values for electronic bits so that you can quickly determine if the fault is with the sensor or if the sensor is giving you good data from a bad part.

And we've come a long way from counting the blinking LED on the ECU. 

David S. Wallens said:

And we've come a long way from counting the blinking LED on the ECU. 

And that used to seem like magic, as long as you had the Little Orphan Annie Secret Decoder Ring.

In reply to Tyler H :

Yes! More than once I sat in the garage counting the blinks from my CRX's ECU.

I actually think that the ability to just count the flashing lights that were already on the car was better in some ways.  The computing and display power - and integration with the various computers that are already in the car - is so great on today's vehicles that there is no excuse for them to not simply integrate the "code reading" functionality into the infotainment system or the digital dash.

At least the early 2000s Chrysler products would display their codes in the digital odometer which was nice.

In reply to wae :

So, basically, why not integrate the OBD II reader? 

I wonder if it's because OEs still have to meet the 1990s-era OBD II spec that requires a certain port for a certain reader? 

Tyler H said:

David S. Wallens said:

And we've come a long way from counting the blinking LED on the ECU. 

And that used to seem like magic, as long as you had the Little Orphan Annie Secret Decoder Ring.

Don't. Forget. To. Drink. Your. Ovaltine.

In reply to David S. Wallens :

Exactly.  And there's no reason that they can't have the ODBII port under the dash while also putting an OBDII code reader "app" as it were on the radio screen or the dash.  The PT Cruiser, for example, could display P codes in the odometer but also had the port.

The E39 BMWs have the ability to display a whole bunch of sensor outputs on the main screen, and that was more than 20 years ago!

They HAVE to have the port, and it has to respond to specific commands and monitor specific things. That's the whole point of the standard :) If you're a Nissan tech and someone rolls in with a Toyota, you can pull the codes and proceed. If the diagnostic info is built into the car and hidden away from the casual user, you're not going to be able to work on that Toyota. So the port is a good requirement.

I agree that it would be useful for DIY people to be able to pull codes directly, and it would not surprise me one bit to hear that some modern cars will put detailed failure info onscreen. In fact, I've seen it. ND Miata is the most likely place of course. I caused a brake error on one of our cars at the track (melted a vaccum line, put the vacuum pump into a high duty cycle) and I'm pretty sure the car gave me enough direct information to diagnose/solve it then and there.

The biggest issue with just posting the codes is that hardly any consumer is capable of dealing with it DIY. In spite of what autozone ads want to make you think. Especially when the warrantee is still in use- don't want the consumer to make it worse. 
 

Also, some of the things covered by the MIL light are covered longer (by law) than others. The reason you even see the light is covered by laws. 

My 2003 Corvette also displays the OBD codes, both active and historical, on the DIC display on the dash. Covers the chassis systems as well as the CEL. 

Oh, and some more info.

Last night, after I wrote this, I saw and old friend of ours who's with BMW NA. I ran this all by him and he seemed to think that we had successfully found the problem. The systems are finicky, he said, as a tiny leak can trigger that light. 

That's exactly the sort of problem - a fuel vapor leak - the systems are designed to check. It's not finicky, it's sensitive and functional. 

Maybe "very sensitive" is the correct term. 

David S. Wallens said:

Maybe "very sensitive" is the correct term. 

Technically, it's 1.5x the certified standard. So the newer, the more sensitive. 

In reply to alfadriver :

Yes, that is exactly what he said. 

Update: No more warning lights. 

Another update: It’s now half a year later and still no more warning light. 

In reply to Keith Tanner :

Is it just me or do factory manuals no longer exist?  Third party one's too, it seems... 

What is it with BMW gas caps?  I've only replaced two gas caps in my life- an E39 528iT, and a Mini Countryman.