# Exhaust Warning Light



## efk141 (Sep 9, 2006)

Yesterday my light went on for the exhaust warning. Does this mean I should now drive with a window open? And how serious can it be? Also, about 2 months ago I was told I need a serpentine belt. Would this have anything to do with the light coming on? I thought I would check with you guys first before calling a dealer. You see, last time I wrote in here, I was told I needed new front brake pads and rotors. I was told from folks here that the dealer's quote was 2X what it should be, so I am hesitating to go back to same dealer. Any suggestions? Eileen


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## car_guy (Aug 19, 2005)

*Re: Exhaust Warning Light (efk141)*

Can you describe exactly what the "exhaust warning" light looks like?


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## efk141 (Sep 9, 2006)

It looks like the outline of an engine with fan at left (it's in orange)


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## Bouviers (Jan 1, 2009)

*Re: (efk141)*

I'm not making a suggestion as to what you should do, but I had the same
situation about a week ago. (see my post entitled My 1st on-the-road Warning light). Mine has not recurred yet though I've been told to expect it again. I had just filled my gas tank the day before and the gas I use contains about 10%
ethanol which as I understand it can sometimes trigger that warning light (as will a myriad of other things). 
Daniel


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## efk141 (Sep 9, 2006)

I think I will let it go for a couple of days and just be careful of airflow. Thanks.


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## chrisj428 (Feb 26, 2005)

*Re: Exhaust Warning Light (efk141)*

Eileen,
What you're seeing commonly referred to as a "Check Engine" light or MIL. This light will come on solid when you're polluting more than you should be due to some perceived failure of the emissions system. The most common cause of this light's illumination is a gas cap being left loose. I would check the cap first and tighten it if it's loose. The light will then go off after about 3-4 days' of driving. 
If not, then schedule an appointment with your service department.
If the light is _flashing_ on and off, do not drive the vehicle, but instead have it towed to your service department immediately for remediation.


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## car_guy (Aug 19, 2005)

*Re: (efk141)*


_Quote, originally posted by *efk141* »_It looks like the outline of an engine with fan at left (it's in orange)

As Chris has said, this is the CEL, or Check Engine Light. It is rarely associated with a leaking exhaust but may have many causes. Usually it is not accompanied by drivability issues, but sometimes it is. If you feel the car is running roughly, i.e., not firing on all cylinders, I would not drive it until it is fixed. Otherwise it can be diagnosed as soon as it is convenient.
BTW, I would doubt that it is caused by a loose gas cap because the Phaeton has a message that displays on the small screen (Y24?) between the speedometer and the tachometer that alerts you to that condition. 
Note to moderators: I don't know how difficult it would be, but it would be great to consolidate all CEL threads to one.
Steven


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## remrem (Jan 20, 2008)

*Re: (car_guy)*


_Quote, originally posted by *car_guy* »_
... loose gas cap because the Phaeton has a message that displays on the small screen (Y24?) between the speedometer and the tachometer that alerts you to that condition.... 
Steven

I didn't know that - very cool! What does the warning look like - does it display an icon of some sort, or does it actually say something to the effect of "gas cap is loose"?


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## car_guy (Aug 19, 2005)

*Re: (remrem)*


_Quote, originally posted by *remrem* »_I didn't know that - very cool! What does the warning look like - does it display an icon of some sort, or does it actually say something to the effect of "gas cap is loose"?

I've actually had this happen twice, but not recently. Neither time was the cap really loose, but oh well... BTW, the trick to see whether your cap is actually loose is not to turn it counter-clockwise but to turn it clockwise to see if it moves without clicking immediately.
As I remember, it definitely displayed a message, and I believe it also then displayed an icon.
This specific warning is becoming more common on cars other than the Phaeton as I've seen it on a few that have come into my shop. It's a great idea because you don't have to read the codes for the check engine light.
Steven


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## Kcmover (Jul 20, 2005)

*Re: Exhaust Warning Light (efk141)*

Does the light look like this?








My Phaeton is in being worked on today as this exhaust warning light was on. But when I asked the service writer what the issue was he said it could be one of many as the car has a lot of sensors on it. 
My car also was having a temperture issue and they want to replace the waterpump and gaskets,thermostat, Tensioners, etc. They are waiting for VW Real Driver Warranty service to approve the job. An inspector for Fidelity has to visit the dealer. It sounds like I should also do the timing belt while they have it apart. Any comments?


_Modified by Kcmover at 11:07 AM 2-18-2009_


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## car_guy (Aug 19, 2005)

*Re: Exhaust Warning Light (Kcmover)*


_Quote, originally posted by *Kcmover* »_My Phaeton is in being worked on today as this exhaust warning light was on. But when I asked the service writer what the issue was he said it could be one of many as the car has a lot of sensors on it. 

I don't know where this started, but we need to stop calling this icon the "exhaust warning" light. Although it may indicate a problem with an oxygen sensor (located in the exhaust system) or a catalytic converter, more often than not it indicates a problem that has nothing to do with the exhaust system. Even problems with the transmission will turn on this icon.
To be consistent with common usage, this indicator should be referred to as the CEL (Check Engine Light or Lamp), or the MIL (Malfunction Indicator Lamp).
The presence of the CEL indicates that a code has been set and stored. A simple code reader (under $100) will read this code and give you an indication of which system is causing the problem. Many parts stores now will let you use one of their readers for free to read the code. 
Unfortunately there is rarely a one to one correlation between a specific code and a component on the car, so further diagnostic are usually necessary to pinpoint the problem.
Steven


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## PanEuropean (Nov 3, 2001)

*Re: Exhaust Warning Light (car_guy)*


_Quote, originally posted by *car_guy* »_I don't know where this started, but we need to stop calling this icon the "exhaust warning" light. 

Hi Steven:
What we really should be calling the thing is the "US EPA Emission Control non-compliance light". This light doesn't even exist on vehicle sold outside of North America.
This light will illuminate whenever the car is not operating in full compliance with American government emission control standards. It does not necessarily indicate that there is anything wrong with the car (although there is _generally _a pretty good correlation between this light coming on and something not working quite right).
The formal name for this light is the MIL, Malfunction Indication Light. Up until the early part of this decade, the formal name for this light was the CEL, Check Engine Light.
Michael


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## noahas (Dec 7, 2005)

I don't have my manual handy, but I assume the reason it is referenced as the exhaust system failure is because that is what it says in the manual for when this light comes on (although I agree about the CEL or MIL, etc., the manual makes some reference to exhaust system failure for this light).


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## PanEuropean (Nov 3, 2001)

*Re: (noahas)*

"Exhaust System" is probably a poor quality translation of "Emission System".
Michael


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## scottmm (Mar 11, 2009)

*Re: (PanEuropean)*

That light is part of your OBDII (On Board Diagnostic) system, the system stores "trouble codes" that will help to diagnose the problem. Most auto parts stores will use their hand-held readers to tell you what codes are in your car. They aren't supposed to reset (erase) the code which will turn off the light, but often will do it as a favor. Write down the code(s) in any case, post them here with your tale of woe. Most trouble codes are standard codes, you can find lists of them online.
The store clerk will need to know where your OBDII connector is, it's a purple connector in the driver's footwell. I think I saw a pic of it in the thread about opening the fuse panel cover. The key must be on, engine doesn't need to be running.
The OBDII system became mandatory in the US in '96, OBDI was much less sophisticated. OBDII monitors all emissions related functions, newer OBDII systems monitor a huge number of sensors and systems. It doesn't involve body safety and convenience functions, like air bags and headlight delays. A separate scanner for that is required.
Parts stores carry OBDII scanners, simple ones are under $100 but don't do much besides show the code and allow you to clear them. I purchased a connector and software for my laptop, it's nice to be able to graph things like oxygen sensor readouts to see if they're truly failed, or maybe it's a vacuum leak (like a loose fuel cap).
-Scott


_Modified by scottmm at 10:21 AM 3-23-2009_


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## PanEuropean (Nov 3, 2001)

*Re: (scottmm)*


_Quote, originally posted by *scottmm* »_That light is part of your OBDII (On Board Diagnostic) system...

Uh, let's be quite careful about how we relate the American emissions light to the OBD system.
The emissions light can be activated by any one of several controllers in the vehicle (engine controller, transmission controller), and those controllers are also active participants in the OBD system. The fault code that has caused the emissions light to illuminate can be read out by using the same facilities that are used to read out other messages from the OBD.
It would be more correct to say that the emissions light is a USA-specific feature that has been appended onto the vehicles OBD system.
The reason I am 'splitting hairs' here is to avoid propagating a widely held belief that the emissions light is an indication of a fault with the vehicle. It is an indication of a fault with the emission control system. Most of the time, *but not all of the time*, faults with the emission control system correlate with vehicle faults. Just ask any W12 owner who has had to replace a transmission because the emission control light illuminates to advise him or her that their fuel economy, when the transmission is in Park, is below acceptable limits due to slippage in the torque converter.
Michael


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## scottmm (Mar 11, 2009)

*Re: (PanEuropean)*


_Quote, originally posted by *PanEuropean* »_It would be more correct to say that the emissions light is a USA-specific feature that has been appended onto the vehicles OBD system.

I'm not sure what you mean by that, but maybe the light has a different intent in Europe?
The system became mandatory in California to help the state with emissions testing. It was quickly adopted throughout the US and eventually some version (EOBD?) was adopted in Europe. The dashboard Check Engine Light was an easy pass/fail for early emissions testing. It was also a great way for auto dealerships to get much more service business. The more things turn on the CEL, the more service business dealerships get and the more parts are sold. Only emission-related malfunctions were supposed to turn on the light initially, maybe they've expanded beyond that now? Some non-emissions diagnostics are accessible through the OBD port, which is nice if you have a scanner.


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## B5Speedo (May 2, 2001)

*Re: (scottmm)*

As long as it is on you are OK. If it starts to blink then don't drive the car.


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## PanEuropean (Nov 3, 2001)

*Re: (scottmm)*


_Quote, originally posted by *scottmm* »_I'm not sure what you mean by that, but maybe the light has a different intent in Europe?

Scott:
European Phaetons don't even have such a light, that is my point.
You are confusing the presence of the emission malfunction indication light with the presence of the on board diagnostic system. They are two different concepts, like apples and oranges. The technician can use the OBD system to find out what turns on the MIL. But, the MIL itself is an add-on device that is not part of the basic specification or design of the OBD.
Michael


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## scottmm (Mar 11, 2009)

*Re: (PanEuropean)*

Ah, no light in Europe. I've only driven rental cars in Europe, only lifted the hood (bonnet?) to see what was in there.
-Scott


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## Theresias (Feb 11, 2004)

*Re: (PanEuropean)*


_Quote, originally posted by *PanEuropean* »_
European Phaetons don't even have such a light, that is my point.

Pardon me, but I think thats not correct. European models have had a MIL since EOBD (the European equivalent of OBD2) was introduced. Specifically that was 2000/2001 for gasoline engines and 2003/2004 for diesel engines. The Malfunction Indicator Lamp (MIL) is a requirement of both, OBD2 and EOBD.
Additional information can be found on this site for example (sorry, haven't found an English language page).


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## PanEuropean (Nov 3, 2001)

*Re: (Theresias)*

Ah, thank you for that correction Sebastian.
Do you know offhand if the criteria for activating the MIL is the same for the NAR and EOBD implementation? The reason I ask is that for one particular problem that affects the torque converters of W12 Phaetons, NAR models activate the MIL (which requires replacement of the torque converter to solve the problem), but ROW models do not activate a warning.
Michael


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## Chris Milnes (Nov 4, 2008)

*Re: (PanEuropean)*

I know of 2 ROW W12 (one being mine) that activated the light for torque converter issues.
After investigation it was discovered that in fact my transmission was low on oil as a result of a leaking sump gasket. 
Since the oil was replaced and gasket replaced some 20,000 miles ago I have had no repeat problem with the torque converter.
Chris


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## Theresias (Feb 11, 2004)

*Re: (PanEuropean)*

No, sorry I don't have the exact specifications. Basically the systems works like this, the ECU recognizes a problem depending on how the ECU software is set up this code can or cannot flag a MIL. Usually a code can have different states (static, intermittent etc.) and also depending on how often its being detected the MIL gets activated or not. I know this is pretty vague but I hope this explains the parts behind it a little better.
As a side note, even though one thinks the base software and therefor the specs should be the same if the engine is the same every once in a while we experience things that simply shouldn't be. So for example my 2.0T flags a camshaft issue regularly but never comes up with a MIL. The exact same code in another 2.0T comes up with a MIL.


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## brosen (Jun 21, 2009)

*Re: Exhaust Warning Light (Kcmover)*

Hi Larry, did they change the Water pump, belt tensioner, etc., today I called Baron VW and asked them for all the Vehicle service records and there is nothing about changing the Water Pump and belt tensioner, the last record is from 2/19/2008 and they did the 60K and brakes, please could you confirm what was done to the car after that date, I am getting closer to 80K and I do not know if I should do those preventive repairs/maintenance or not, thanks


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