Check engine light


I have a 2004 Audi A6 wagon that’s got 105k miles on it. A couple months ago, the check engine light came on while I was driving it. While it was on, it was flashing and the car felt like it was shuddering, like there was not enough gas getting to the engine. Then the CIL stopped flashing. It happened several times during my short outing that day, but then it never happened again. Now the flashing CIL is back and the car feels the same way when it’s happening. I took it to an auto parts store to get the trouble codes read and the guy said P0300 (random cylinder misfire) and P0305 (cylinder 5 misfire) came up. Does anyone know what is causing this problem, how serious it is and how expensive it’ll be to fix it?

Forgot to mention, I also have bits of foam blowing up from the air vent on my dash. Although I’m not sure if the two problems have anything to do with eachother. Thought I should mention it just in case!

Lots of things can cause this problem. Here are a few: old spark plugs & wires, damaged/failing distributor and/or coil or coil pack (depending on your set up); poor engine compression; poor fuel pressure; clogged or otherwise failing fuel injectors; damaged/failing wiring to any number of components etc.

How old are the plugs & wires? Air & fuel filters?

Have the fuel pressure checked.

If you have the spark plugs changed, have the compression checked while they’re out. If the plugs have been changed recently they should be inspected - and compression should still be checked.

It should be mentioned that a flashing check engine light means to stop immediately, turn the car off, and have it towed. Misfires can cause a lot of very expensive damage if you let them keep happening.

How Long Have You Owned This Car ?
I’d Give The VIN (Vehicle Identification Number) To The Service Manager/Director At An Audi Dealer And Have Them Check For Any Service Campaigns (Voluntary Recalls) And/Or TSBs (Technical Service Bulletins) For This Vehicle.

During your discussion they can give you an estimate for giving you a diagnosis and estimate.

I do see some bulletins pertaining to misfires and codes like the ones you’re getting and mention of a service campaign. Best you check with the horse’s mouth to see what applies and also if there’s record that any have been performed on this vehicle.

The car should not be driven with a flashing CEL or engine damage can result.


I have to agree with CSA on this one. You may even need to have a full diagnostics performed to get to the root cause. That may cost you upwards of $150, but could save you money in the long run. Just throwing random parts at it can get very expensive and not accomplish anything.

Be very clear with the dealer that you want more than just someone reading the codes, they need to open up the service manual and follow all the troubleshooting procedures related to the codes they get.

I BELIEVE that Audi’s of this vintage had a big recall on all of their coils Not sure if the affected ones were made by Bosch or not so…there was something wrong with the electronics or with the coils that were causing a lot of failures… Does your vehicle fall under this coil recall? Methinks it might… Maybe you never had your coils replaced under this recall and they are starting to act up? I have had first hand experience with faulty coils on an 03’ or 04’ Audi A4 I think it was… It was a V6 also… They use the same coils across many of their models so…

VERY MUCH worthy of looking into this coil recall. I remember there was a big rash of Audi/Coil/misfire issues a while back… I was in the thick of it back then and relieved to hear of the coil recall issue…solved the problem right away. AGAIN…not sure if the culprits were made by Bosch or was it FIXED BY BOSCH or not…so…

My friend had all of his coils replaced free of charge a while back when the exact same things began happening to him…

I pulled this off the net for you:

February 5, 2003
Volkswagen and Audi will recall more than half a million vehicles to replace a defective ignition coil that leaves the cars prone to sudden power losses and potential engine damage.

Spark plugs and wires, fuel & air filters is not “throwing parts” at something. Has anyone in this thread suggested throwing parts?

Don’t believe this vehicle has wires …fairly certain its Coil over plug.

If I were the owner I would be digging Quickly and Deeply into the recall about those coils…

Dont you guys believe me or something? LOL

I know for certain that Audi and VW had MUCHO PROBLEMOS…with a rather long run of Bosch coils and what the actual fault was I don’t know…but I do know the coils were suspect.

I called my bud with the A4 and he reminded me that the issue was CREATED and then SOLVED by Bosch… SO Bosch had a run of faulty coils and they caught it…so they released a new P/N for an updated/corrected coil and replaced all the ones that they could ID out in the real world.

Bet this is the problem with your Audi…

Thanks everyone for your comments and suggestions. As someone that doesn’t know much about cars, these are all good points to consider. I have an appointment to take the car to the dealership Friday. The car is a 2004 and we bought it used in 2007. My husband seems to remember receiving something in the mail about the coil recall and he thinks we took it in, but doesn’t think they replaced them…for some reason. We have to go back through our files to figure out what happened exactly. I just hope that they’ll replace the defective part(s) for free and that there wasn’t additional damage done to other parts of the car.

Sounds good…Not sure what the protocol is with a vehicle not brought in and repaired in time for a recall…but press the point and make sure they get those suspect coils outta there. They can cause engine damage from what the recall says… At least you now have something to go on…No?


It’s always good to be knowledgeable when walking into a situation where there’s bound to be a dispute…especially if it can save lots of $!

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

All of the faulty ignition coils in my car were replaced with the updated ones (per the recall) in July 2010. Is there a chance that the new coils could be bad as well?

"Is there a chance that the new coils could be bad as well?"
Sure, There Is A Small Chance, But It Could Also Be One (Or More) Of Many Other Things.

When it’s very, very dark ouside ( new moon) and you open the hood with the car running (BE CAREFUL - keep clear - no loose clothing, etcetera ) and you observe the engine, you should not see any “fireflies” or even faint sparking anywhere. I doubt this is going on, but you could check it. Sparks would indicate an ignition problem that could cause a misfire, but again, other things can cause a misfire . . . compression problems, fuel-air mixture problems, etcetra. This is pure guessing.

The car needs to be properly diagnosed.


Well the Audi dealership said they’re not sure what’s causing the problem but they want to “start” by replacing the spark plugs and air filters. This will run me $500. This is the kind of thing that really burns me up about these guys. The implication is that they could do the work but it may not fix the problem, which would require more money to try their next hunch. When you take this together with the $2200 they want to replace the timing belt, I may as well trade it in and get something new and more reliable. This car has been such a money pit and a terrible disappointment.

 Why are you taking it to an Audi dealer?

    Dealers are no better (or worse) than independent mechanics for almost anything you might need done on your car.  They will almost always charge more per hour and often more for parts and supplies.  They also tend to look at repairs a little different than the independent. 

A dealer may well recommend work that strictly may not be needed, but could be connected to the problem or maybe replace a part when a little repair would fix it ALMOST as good a new.  

There is no need to bring your car to the dealer for any service other than service that is going to be paid for by a recall or original warrantee.  During the warranty period be sure to have all required (as listed in the owner's manual) maintenance done and to document all maintenance work.

I suggest that most people would be better off finding a good independent (Not working for a chain) mechanic. 

Note: Never ever use a quick oil change place. They are fast cheap and very very bad.

The OP can click on the ‘mechanics files’ button at the top o’ the screen to find a good indy mechanic.

Just my opinion, but any mechanic or shop that replaces coils without considering the plugs is on shaky ground, mechanically speaking.

Most coil failure, IF it’s legitimate, can be traced to aged and/or misfiring plugs over the long term or moisture in the plug wells, etc.

At this point I don’t know that you have an Audi problem as much as a mechanic problem.