Cold Morning, Service Engine Soon, Engine Rattle


Hi all,

I have a 2006 330i with 69k miles.

Just this morning, it’s about 25F, I started my car and noticed the car shakes a bit due to the engine is rattling. I idle the car for a bit but it didn’t go away. When I drove the car away the service engine light came on.

The engine just doesn’t perform as it used to be compared to last night, it’s louder, sluggish, doesn’t accelerate as before, and rattles even I drove it all the way to work.

All I remember doing was I just filled the car up the previous night. And the car is due for an oil change.

Any helpers? Thanks

By “service engine” light, do you mean the “maintenance due” light or the “check engine” light (CEL)? The CEL is telling you that a sensor has detected an operating problem and the computer has stored it for further diagnosis by a mechanic.

Either take it to a shop, of if you’d like to try to work on it yourself have the fault codes downloaded at a parts store and post them here.

The exact word is “Service Engine Soon”. It’s not the regular maintenance due warnings from the LED screen at the lower portion of the dash. This light is on the upper portion of the dash slightly to the right.

I’m concerned and wondering if bad gas can cause something like this be cause I just filled up from a random Shell station a night before? Or this can be something totally unrelated.

It could, but in truth bad gas gets blamed for far, far more problems than it actually causes. I’d strongly recommend getting the codes read for starters.

I just got the call back from my SA, he told me it’s a bad coil, good thing this is covered under warranty. But I just kinda curious as to what this coil he is referring to?

The ignition coil. Your car has a seperate ignition coil on each sparkplug.

The ignition coil is an inductive device that basically turns the 12VDC into a spike of the thousands of volts necessary to jump the gap in the spark plug. 12 VDC is allowed to flow through a coil wrapped around an iron core. That creates a magnetic field within the coil and the core. When the spark plug needs to fire, the 12VDC is suddenly removed. The magnetic field in the coil collapses into the core, creating a voltage spike of tems of thousands of volts.

In old cars there was a single coil, and the spike was distributed to the appropriate spark plug through the distributor. The distributors also contained the control mechanism to enable and disenable the 12VDC in the coil mindings. Going way back, it was a simple mechanical on/off switch called “points”. Eventually it became a non-contact device called an “igniter”. In modern car, like yours, the engine’s computer controls the coil current based on a sensor reading of where each piston is combined with a sensor measurement of the speed of the engine. One signal, one sensor, can tell the computer both, or two can be used, one for position and one for speed.

In your case, apparently one of the coils failed. It’s a minor failure. And, because you were smart enough to get it fixed immediately, it will stay minor and leave no lasting effects.

Thank you so much for the detailed explanation.

You’re entirely welcome. Have a great weekend.

My dealer replaced the plug and coil in Cylinder 3, the car drives fine now, but after a day the light came back on, however the car drives and feels fine… what gives :frowning:

There’s no way of guessing without rechecking the codes. I’d recommend doing so at your earliest opportunity.