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My Malibu is giving me headaches... Literally!

My 2001 Chevy Malibu is giving me a headache while I’m driving. Initially my wife told me that it’s psychosomatic, until she started getting headaches too. At first there was a smell, my mechanic replaced the EGR valve, replaced the water pump and a couple of hoses. No smell now, the exhaust has been checked out seems to be fine. The headaches still persist. I had the car checked for CO-2 by the fire department and it seems to be fine. What is causing these headaches?
The gas tank seems to be having a pressure issue when I fill it, could that be the problem? The mechanic has gone through it, doubts it’s the gas tank and really can’t find the problem. The car is in great shape otherwise and only 79,000 miles on it. It would be a shame to get rid of it.


John Moses


Here’s my suggestion . . . have that mechanic use an evap/smoke machine to check for exhaust leaks. The shop he works at should have one

I’ve had great success finding exhaust leaks using one

I suspect you have an exhaust leak near the exhaust manifold, which is being pulled by your ac system’s fresh air intake

The reason you’re getting a headache is this: the oxygen sensor is measuring the unburnt oxygen from this leak. The pcm assumes the mixture is lean, so it commands more fuel. So now you actually have a very rich mixture. Which is leaking out of that crack, bad gasket, etc. Which is getting pulled into the cabin by the ac’s fresh air intake

Seen it before

Very dangerous to drive a vehicle in this condition

Thanks heading there now… With this info…

“I had the car checked for CO-2 by the fire department and it seems to be fine. What is causing these headaches?”

It’s all well and good that the fire department found no CO2, but if you have an exhaust leak, that would likely result in CO (not CO2) seeping into the passenger compartment.

CO2 (carbon dioxide) is relatively benign, but CO (carbon monoxide) is deadly. The first stages are characterized by headaches, but after a period of time, brain cells begin to die, then you fall asleep, and you die–unless oxygen is administered immediately by First Aid personnel.

Follow 4690’s advice and after the repair, please be sure to have the car’s interior checked for CO, not for CO2.

There are inexpensive battery operated CO detectors available at hardware store I think. Might be worthwhile investment.

Right, thanks guys. I actually think they checked it for CO

The Fire Dept would have checked for CO (carbon monoxide), almost every dept has a portable CO detector, I doubt any Fire Dept has a CO2 detector, like VDC said big difference between the two. They likely checked for CO when the car was stationary, the leak in your car may be intermittent or not show up until it is warmed up or ???. Like George says a battery operated home CO detector can be used, home CO detectors have a long response time (to prevent false alarms) Read the manual that comes with it, you may have to drive for a half an hour to get it to full scale. Headaches are typical of CO poisoning, you have to have a fairly high level of CO to get a headache, you want to get this checked and fixed ASAP

Are those detectors that turn brown in the presence of CO sensitive enough to work in this application, or are they more of a “you’re about to die” device?

Maybe the headaches are caused from the outgassing of the materials used in the interior of the vehicle.


The ones that turn brown (one time use) pretty much tell you that you have a problem and need to check with a monitor for more reliable results.

@Tester: Outgassing seems unlikely in a 13 y.o. car, especially in cold weather.

The OP didn’t state where they were located.

Outgassing can occur at anytime in a vehicles interior. I’ve seen fifteen year old vehicles start building a film on the inside of the windsheild because the plastic/vinyl dash started to outgas.


@Tester Thank you! My 2010 KIA Forte SX has always had a film problem on the interior windshield. Windex and other cleaners are ineffective. This could be the cause. I am taking it to the dealer soon for a brake light switch recall. I will pitch a b*tch about this problem.

@db4690 I took it to a mechanic and he ran the smoke/evap machine. He couldn’t find the problem. I’m at a loss

Maybe there is a clogged drain tube causing mold. Canging a cabin filter if applicable won’t hurt anything.

Does the ac smell musty? The evaporator could need cleaning.

I’ll look into it fellas. Thanks!

Ac leaking under dashboard where it comes through firewall