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In my 2003 Opel Vectra, the cabin air smells of Diesel exhaust while stopped at e.g. a red light.
The exhaust smell goes away when driving, and it also doesn't come back if I turn the ventilation off before stopping at a light. It's not temperature-related: it happens whether it's cold or warm outside, and also whether or not the engine has reached its normal operating temperature. It also happens whether or not the A/C function of the ventilation system is turned on. The car's windows are always closed.

It seems to me that there is some problem with the car's ventilation and/or exhaust system. I'm fairly sure it's not a problem with the A/C itself as it's not a chemical odor but clearly an exhaust smell.

Asking the dealer, he told me that the car has a Diesel-powered auxilary heater that engages when it's cold outside and the engine isn't warm yet. While that heater is working, the heated cabin air might have a weak Diesel smell.
- This explanation would make sense to me if it didn't happen in the summer too (when the aux heater is presumably not used), and if it did happen while driving, but neither is the case.

1. What could be wrong with the car?
2. Is it dangerous to drive? (carbon monoxide gases)

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Torben Gundtofte-Bruun
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5 Answers5

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My first concern is that you have an exhaust leak. The exhaust is designed to exit at the rear and or side of the car, far away from your fresh air intake of the ventilation system in the cowl area. I would check for an exhaust leak starting at the front as you stated that it's coming in from through the ventilation system.

This can be dangerous and should not be ignored, you could be overcome by the exhaust which can contain Carbon Monoxide.

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Update: The problem was indeed a leaky exhaust system! Alarmingly, the service shop I had tasked with the repair did not find this leak, but another authorized dealer found and fixed it.

I'm horrified that a repair shop can manage to not find a fault like this, but glad to note that I'm not stupid: there really was a problem. Since then, I've sold the car for unrelated reasons.

Original post:

To follow up, here is how the problem was solved:

The A/C was cleaned and disinfected, the coolant was replaced, and the cabin air filter was replaced by a carbon filter. This is something I like to have done every few years, for the sake of the health of the passengers, and it was long overdue on this car.

Still not sure where the smell came from, but apparently the new filter (and the cleaning) takes care of it.

Torben Gundtofte-Bruun
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A Diesel Engine will not emit carbon monoxide no matter what. The Diesel engine, even at idle, has a ratio of fuel / air much-much lower than a typical gasoline engine. Therefore there's more than enough Os for the Cs (oxygen for the carbon) so no monoxide will ever be produced.

There could be other harmful gases in the exhaust or at least it's annoying to smell. It simply shouldn't happen so there definitely is a problem, most likely, as you reported, an exhaust leak.

It can also happen while going in reverse or when there is a strong wind from behind.

Andrei Rînea
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Just had our mechanic friend look at ours which was giving off a smell in the cabin and making a fluttering noise and it was a loose injector. Watched him tighten and sort in seconds. Quote from garage for new injector - not needed for £400...citroen diesel.

Nathan
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Loose injectors will result in combustion gases blowing back up the injector. Will result in exhaust gases leaking into engine bay.

Matt Mckenzie
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