a car question! the Check Engine light.
 

well, DUH!! the other day, the CEL came on in my wife's Subaru. it was alarming to say the least since we were far from home. car seemed to run fine.

when i got home, i took the time to think about "what has changed?". it hit me. i changed the engine air cleaner because everything up here has been sucking in sooty smokey air. (filter was black!). i neglected to close up the airbox tightly, and inadvertently left a corner unclipped.

i hooked it all down correctly, double checked, triple checked..and disconnected the battery. upon start up..no CEL!

that it? done?

how does an aftermarket cold air intake not trip the CEL? i was shocked a tiny bit of air whizzing past the element would trigger the CEL.

It’ll go away until you’re in a bad neighborhood late at night to maximize irritation and paranoia (or right before a vehicle inspection check), then it’ll come back. :)

A reset sometimes clears the faults. On my Sienna for some reason the VSC system warning light lit up while on the freeway. Having done nothing to the car nor have I used it on bad roads in the last 3 months, I simply disconnected the battery for a few minutes (or more precisely just the black wire), hooked it back up, and warning is cleared. Have driven it a few times and no issues so far.

On the other hand, my Cayenne first showed a "reduced engine power" light. And now it's a CEL. Car runs fine, unless you try to accelerate. Probably in limp mode and running on 4 cylinders. Since the battery is under the driver's seat, I wasn't going to bother, but will take it to an indy for diagnosis. The only two things I did were: 1) I tried to jump start the 911 with the Cayenne while forgetting to start the Cayenne first (stupid move) and 2) I put Techron complete fuel system cleaner a week ago. This might be more of a coincidence. But it could have exposed some part in the fuel system that is nearing its end of life, like the fuel pump.

Plug a code reader in and see what codes are stored.

You can borrow a code reader for free at the FLAPS and they'll tell you what the code says. Some of them have a reset (if you read the manual) but they won't tell you how to do it.

The check engine light is the most reliable part on a BMW .

That, and your gold Mastercard to pay for maintenance and repairs.

The wife’s 2002 Camry loved nothing better than a new gas cap to get rid of the CEL.

I think the dealers are able to automatically engage the CEL whenever their service revenue dips for the month.

^^^^^^^possibly the best quote in awhile........I'm filling that one away. Especially any 'M' car.

Some auto part stores will check for stored DTCs for free.
They plug in a scanner. Read stored trouble code. And then suggest the correct muffler-bearing lube.

The dash light probably won't come back on until drive cycles are completed. If at all.

Until then, check all fluid levels and filters for condition.
Drive normally. Watch gauges.

CEL (check engine light) is OBD1.
Pre-1996.
(There was a 1994-1995-1996 overlap with Canadian made vehicles IIRC. My 1995 Legacy was OBD2.)

MIL (Malfunction Indicator LampLight) is OBD2.
Anything after 1996.
It incorporates everything including transmission powertrain, intentionally self-testing systems by activating EGR to look at O2 sensor response, ABS sensors, and all the nonsense.

The drive cycles have to complete over time. Start-stop. Freeway. WOT. Cruse. Braking. All of it. It is probably different for different mfrs.
The short-term long-term fuel curves also have to be set.

MIL is the correct terminology to use.

+1

All OBD codes were cleared and the monitors were reset when the battery was disconnected.

You are starting from scratch. Your car has to run the self checks.

It can take a while.

Yes, it is different. My favorite step is to drive 60 for six minutes and then pull your foot off the gas and coast down to 20 mph without touching the brakes.

I can go 60 mph on I77 for six minutes but have to find an uphill grade and put the car on the shoulder to slow down to not end up as a grease spot.

FLAPS???? Battery???


Buy this cheap Chinese bluetooth OBD reader:
https://www.amazon.com/gp/product/B00PJPHEBO

Put Torque on your phone. Then pay for Torque pro.

You can now get your own codes whenever, clear them, and see why they're there. You also know if you've put enough miles on to pass emissions after clearing the codes.

You also get fun little gauges for all sorts of things that your car doesn't tell you right now.

For 13 bucks I just ordered it... I'll check the Torque app later.

I loaned my old Subie to my nephew once. The CEL was always on. He calls and says "The check engine light is on" I tell him "Pop the hood". He says "Okay" I say "is the engine still there?" He says "you're an ass"

My favorite CEL illumination comes from the gas cap not being on tight. :mad: That's not the engine!!

Throwaway Chinese readers might be infested with permanent CCP apps.

I suggest getting the standalone model specific scanners. They pay for themselves after saving one trip to the shop.

Then the CCP might know your gas cap is not sealing. Or worse, the songs you are listening to?

I say nut up and buy a slightly more expensive reader with Parameter ID's. The CCP version is probably $50. An Actron at your FLAPS is $250.

yes quite often I check under the hood, and the engine is still there.

Or what your webcam sees ...

The Icarsoft stuff is what I use for the other cars.

https://www.icarsoft.com/Product/s-299-iCarsoft_MB_V1.html

You know, I did buy a basic CCP Vag-Com reader (emulator) online. No PID's but airbag/ABS.

The Vag-Com code descriptions in the provided booklet gave a broader base of culprits then the OBD code descriptions. One fix from the el-cheap-o Vag-Com paid for it AND the expanded OBD with PID reader.

Specific issue was the ever present VW coolant temp sensor code. Booklet said could be thermo housing and/or thermostat also so I replaced both. Not real scientific but a better clue than with what OBDII codes gave me.

CAI and airbox are before the MAF.
Your airbox probably did not trigger the CEL.
Read the stored codes

Yepper. Betcha gas cap or some evap code.

Stored codes are gone if battery disconnected as OP said, unless some snazzy scanner can pick them up.

The Mercs use a different diagnostic system, SDS. Last time I used it, found the speed sensor was the culprit for the ABS light. Was interesting graphing out the fuel trim on the Accord as well and seeing the adjustments made at different running conditions., But yes, one fix will pay for the unit especially on anything of German make !

Thanks. I’ll do it. I didn’t think the airbus leak would trigger the CEL. I’m hoping the gas cap gasket is the culprit.

Typically it's something emission related. You could have an upstream or downstream o2 sensor on the fritz, could be a cylinder misfire that popped up and went away. When you check the codes report back.

I've driven cars with the CEL on knowing that it was a P0420 code. I got tired of looking at the light on my Taurus and finally replaced the catalytic converter that was pretty much shot. My Subie, I tried to fix the problem a few times and just gave up. It didn't hurt mileage or performance so it became a mind over matter thing, if I don't mind, it don't matter.