Tech Tip: Tips to Detect a Vacuum or Exhaust Leak

Subject: Some Customers may comment that their vehicle’s Malfunction Indicator Lamp (MIL) is illuminated. Upon initial diagnosis, technicians may find one or more of the following fuel trim and/or O2 sensor related DTCs set: 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 or P2273.

Vehicles involved: 2000–2020 GM passenger cars or trucks with gasoline engines (only)
The GE-52250 Variable Pressure Leak Detector is the preferred and most effective method.
If normal Service Information (SI) diagnostics do not lead to a resolution and an intake vacuum leak or exhaust leak is suspected, one of the following tools/methods may be useful in finding the source.
The GE52250 Variable Pressure Leak Detector is the preferred and most effective method. (For information on use of the tool, see Component/System Leak Test: SI Doc #5433806.) In addition, a J-41416 Ultrasonic Leak Detector can be used — or simply applying soapy water and low air pressure. Note that these methods are more effective if the vehicle’s throttle body is covered/ sealed.
For a suspected intake vacuum leak, use the variable pressure detector to inject smoke into the brake booster hose or the oil dipstick tube. Spray soapy water near the gasket and seams and on all the vacuum nipples to check for leaks.
For an exhaust leak, applying soapy water around the seals, seams and bosses, and then injecting smoke or air into the tailpipe often proves effective. An ultrasonic leak detector may be used here as well. The above methods are good for finding small leaks around the O2 sensor embossments and when checking for slight cracks in an intake plenum or gasket.
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