A Sensible Smoke
This bulletin applies to 2000-2012 GM passenger cars and light-duty trucks equipped with gasoline engines, where the SES light is on and any of the following fuel trim and/or O2 sensor-related codes are stored:
P0101, P0137, P0138, P0140, P0141, P0157, P0158, P0160, P0161, P0171, P0174, P0420, P0430, P1174, P1175, P2096, P2097, P2098, P2099, P2177, P2178, P2179, P2180, P2187, P2188, P2189, P2190, P2270, P2271, P2272, P2273.
If normal diagnostics does not lead to a resolution and an intake vacuum leak or an external exhaust leak is suspected, the use of a smoke machine may be useful to find the leak. For an intake leak, the smoke can be introduced into the brake booster hose or the engine oil dipstick tube. For best effect, covering the air intake before the MAF sensor to allow air pressure to build is recommended.
For an exhaust leak, the smoke machine hose is placed into the tailpipe, sealed with shop towels. This method is very good for finding small leaks around the O2 sensor bosses and slight cracks in an intake plenum or gasket.