Figuring out what that warning light actually means

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David S.
Update by David S. Wallens to the BMW M3 project car
Feb 27, 2024 | BMW, BMW M3, M3, E46 M3, E46, Warning Light


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 indicates a fault …

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Colin Wood
Colin Wood Associate Editor
12/8/22 12:33 p.m.

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


David S. Wallens
David S. Wallens Editorial Director
12/8/22 12:47 p.m.

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. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
12/8/22 12:55 p.m.

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.

David S. Wallens
David S. Wallens Editorial Director
12/8/22 1:03 p.m.

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....

wae PowerDork
12/8/22 1:27 p.m.

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.

David S. Wallens
David S. Wallens Editorial Director
12/8/22 1:38 p.m.

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

Tyler H
Tyler H GRM+ Memberand UberDork
12/8/22 2:35 p.m.
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.

David S. Wallens
David S. Wallens Editorial Director
12/8/22 2:42 p.m.

In reply to Tyler H :

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

wae PowerDork
12/8/22 2:42 p.m.

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.

David S. Wallens
David S. Wallens Editorial Director
12/8/22 2:50 p.m.

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? 

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