GMC 1995 Suburban Owner's Manual page 103

Engine Exhaust
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CAUTION:
Engine exhaust can kill. It contains the gas carbon monoxide
(CO), which you can't see or smell. It can cause unconsciousness
and death.
You might have exhaust coming in if:
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Your exhaust system sounds strange or different,
Your vehicle gets rusty underneath.
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Your vehicle was damaged in a collision.
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Your vehicle was damaged when driving over high points on
the road or over road debris,
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Repairs weren't done correctly.
Your vehicle or exhaust system had been modified improperly.
If you ever suspect exhaust is coming into your vehicle:
Drive it only with all the windows down to blow out any CO;
and
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Have your vehicle fixed immediately.
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