Manufacturer communication — 2006 GMC YUKON DENALI XL

• Applies to 2015 and prior passenger cars and trucks.

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  Models: 2015 and Prior Passenger Cars and Trucks

• The service engine soon lamp (MIL) is on with DTC P0442, but no leak can be verified with the system test in the service information.

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  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. Connect the scan tool and command the EVAP system closed.

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   Connect the scan tool to the vehicle and command the EVAP system CLOSED.

2. Start the engine and watch the fuel tank pressure sensor value for about two minutes.

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   Start the vehicle and monitor the tank pressure sensor output value for approximately two minutes.

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

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   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.

4. If the sensor 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.

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   Install CH-48096 adaptor between the purge line from the canister and the purge solenoid. Do not use any other adaptor or pressurization method.

5. With the EVAP system closed, pressurize through the CH 48096 adaptor and watch the pressure/vacuum gauge for at least 5 minutes until the system is fully stable, then add smoke.

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   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.

6. Check the canister vent solenoid filter or fresh-air line for smoke; an intermittent vent solenoid fault may show up when the vent solenoid is cycled and the test repeated.

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   Canister vent solenoid filter or fresh-air line - Note: An intermittent condition with the vent solenoid may be exposed by cycling the vent solenoid and reperforming the test.

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

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   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

• Add smoke and let the pressure stabilize; if smoke passes through the purge solenoid, replace the purge solenoid.

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  Add smoke and allow pressure to stabilize for 2 minutes. 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.

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

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

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  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.