Technical Service Bulletin PIT4943C — 2004 GMC CANYON

This Preliminary Information communication provides information to the technician about vehicles that have a Service Engine Soon Malfunction Indicator Lamp. Technician may find Diagnostic Trouble Code P0442. Technician will need to review Techlink article from May 2013 titled "Using the Evaporative Emissions System Tester" Technician will need to follow these steps to help diagnose the issue. First after the P0442 has been verified do not disturb any of the fuel system components. The technician now can use the scan tool to close the Evaporative Emissions System. If possible change the tank pressure sensor units from inch_H2O to milimeter_Hg for better resolution. Now the vehicle can be stared to monitor the tank pressure sensor output value for approximately two minutes. If the tank pressure sensor value does change, pressurize the fuel tank side of the purge solenoid with the GE 41413-A / J 41413-A and the necessary adaptors. Now add smoke and allow pressure to stabilize for 2 minutes. If smoke is allowed to pass through the purge solenoid, replace the purge solenoid. If the tank pressure sensor value does not change, then install CH-48096 adaptor between the purge line from the canister and the purge solenoid. With the Evaporative Emissions System closed, pressurize the system through the CH-48096 adaptor and allow the system to completely stabilize, by observing the Press / Vac Gauge for a minimum of 5 minutes. Now add smoke to the system with GE 41413-A / J 41413-A after system stabilization. Now inspect the purge solenoid, engine side, fuel cap, canister vent solenoid filter and any line quick connects. When the leak is unable to be located, test under a vacuum condition. his type of leak may be detected by using the scan tool Purge/Seal function to create a vacuum in the Evaporative Emissions System and then observe the FTP sensor parameter for vacuum decay.