GMC 2007 Envoy - Manual (Page 401)

{ CAUTION:
Operating the engine with the air
cleaner/filter off can cause you or others
to be burned. The air cleaner not only
cleans the air; it helps to stop flames if
the engine backfires. If it is not there and
the engine backfires, you could be
burned. Do not drive with it off, and be
careful working on the engine with the air
cleaner/filter off.
Notice: If the air cleaner/filter is off, a backfire
can cause a damaging engine fire. And, dirt
can easily get into your engine, which will
damage it. Always have the air cleaner/filter in
place when you are driving.
Automatic Transmission Fluid
When to Check and Change Automatic
Transmission Fluid
A good time to check your automatic transmission
fluid level is when the engine oil is changed.
Change the fluid and filter at the intervals listed in
Additional Required Services on page 510, and
be sure to use the transmission fluid listed in
Recommended Fluids and Lubricants on page 517.
401