Why do I sometimes smell exhaust fumes in my car when I am driving? My passengers have also complained about this.
Exhaust smell in an air-conditioned cabin is a cause for concern.
If the air-conditioner's fresh air inlet is open, exhaust gases could find their way into the cabin through the ventilation system. Switching to the recirculating mode would alleviate this, but may not eradicate it. It depends on how well the inlet duct seals shut.
Infiltration of gases into the cabin will also occur if the seals of the rear doors, boot or tailgate are worn. On the move, the aerodynamic characteristics result in a high-pressure region at the rear of the car and any broken seal will allow access to exhaust fumes.
In some cars, a one-way flap that serves to discharge cabin air pressure when closing the door could become dislodged or stuck open. This is another avenue for gas ingress into the cabin. The flap is usually found somewhere near the rear wheel well and is often not easy to locate.
A cabin smelling of exhaust is an unhealthy situation which must be rectified immediately.