Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to 2016 and prior passenger cars and trucks.

  the passage

  Models: 2016 and Prior Passenger Cars and Trucks

• The service engine soon lamp (MIL) is on for DTC P0442, but a leak cannot be verified with the system test in the service information.

  the passage

  Vehicles are illuminating the service engine soon (MIL) due to a P0442 diagnostic trouble code (DTC), but a system leak cannot be verified through the system testing instructions identified in SI.

Steps to confirm (in the document’s order)

1. With the scan tool, command the EVAP system CLOSED, start the engine and watch the tank pressure sensor value for about two minutes.

   the passage

   2. Connect the scan tool to the vehicle and command the EVAP system CLOSED. 3. When possible change the tank pressure sensor units from in_H2O to mm_Hg for better resolution. 4. Start the vehicle and monitor the tank pressure sensor output value for approximately two minutes.

2. If the tank pressure value changes (shows vacuum), remove the purge solenoid and pressurize its fuel tank side with the GE 41413-A / J 41413-A tester.

   the passage

   5. If the tank pressure sensor value DOES change (shows vacuum): 5.1. Remove the purge solenoid from the vehicle. 5.2. Pressurize the fuel tank side of the purge solenoid with the GE 41413-A / J 41413-A and necessary adaptors.

3. If the tank pressure value does not change, install the CH-48096 adaptor between the purge line from the canister and the purge solenoid; use no other adaptor or pressurization method.

   the passage

   6. If the tank pressure sensor value in step 5 DOES NOT change 6.1. Install CH-48096 adaptor between the purge line from the canister and the purge solenoid. Do not use any other adaptor or pressurization method.

4. With the EVAP system CLOSED, pressurize through the adaptor and let the system stabilize, watching the gauge for at least 5 minutes, then add smoke.

   the passage

   6.2. With the EVAP 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. 6.3. Add smoke to the system with GE 41413-A / J 41413-A after system stabilization.

5. Look for smoke or UV trace fluid at the purge solenoid, the engine side, the fuel cap or capless fill door, and the canister vent solenoid filter or fresh-air line.

   the passage

   6.4. Review all of the critical interfaces for any smoke and/or UV Trace fluid: – Purge solenoid – Engine side (remove quick connect or unbolt from manifold) – Fuel cap or capless fill door – Canister vent solenoid filter or fresh-air line

6. If smoke testing finds nothing, the leak may exist only under vacuum: use the scan tool Purge/Seal function to pull a vacuum and watch the FTP sensor parameter for vacuum decay.

   the passage

   7. If unable to locate a leak by smoke testing, a condition may exist where a leak in the EVAP system only exists under a vacuum condition. This type of leak may be detected by using the scan tool Purge/Seal function to create a vacuum in the EVAP system and then observe the FTP sensor parameter for vacuum decay.

Repair

• If smoke passes through the purge solenoid, replace the purge solenoid.

  the passage

  5.4. If smoke is allowed to pass through the purge solenoid, replace the purge solenoid.

Caution

• After verifying P0442, do not disturb any fuel system component before testing.

  the passage

  1. Do not disturb any of the fuel system components after verification of a P0442 on a vehicle.

• Test pressure must not exceed 13 in H2O (0.5 PSI (= 3.45 kPa)); more can make components perform inaccurately and lead to misdiagnosis.

  the passage

  When servicing the EVAP system, test pressure must not exceed 13 in H20 (0.5 PSI) as pressure in excess of this could cause system components to perform inaccurately, which can lead to mis-diagnosis.

• A large temperature difference between vehicle, shop and tester seriously affects accuracy; let the vehicle adjust to shop temperature first.

  the passage

  A large temperature difference between the vehicle, shop and EEST will seriously affect the accuracy of the tests. Significant differences in temperature between them can result in a flow or pressure change during testing, causing misleading results. Always allow the vehicle temperature to adjust to the shop and EEST temperature, which can lead to mis-diagnosis.