From the shop manual:
DTC P0442
Evaporative Emission (EVAP) System Small Leak Detected
CIRCUIT/SYSTEM DESCRIPTION
The engine off natural vacuum (EONV) test is the small leak detection diagnostic for the evaporative emission
system. This diagnostic tests the evaporative emission (EVAP) system for a small leak when the key is turned
OFF and the correct conditions are met. Heat from the exhaust system is transferred into the fuel tank while the
vehicle is operating. When the vehicle is turned OFF and the EVAP system is sealed a change in the fuel tank
vapor temperature occurs which results in a corresponding pressure change in the fuel tank vapor space. This
change is monitored by the engine control module (ECM) using the fuel tank pressure sensor input. With a leak
in the system, the amount of pressure change will be less than that of a sealed system.
CONDITIONS FOR RUNNING THE DTC
DTCs P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0222,
P0223, P0443, P0446, P0449, P0451, P0452, P0453, P0454, P0455, P0461, P0462, P0463, P0464,
P0496, P0502, P0503, P0608, P0641, P0651, P1516, P2101, P2119, P2120, P2122, P2123, P2125,
P2127, P2128, P2135, P2138 are not set.
The ignition 1 voltage is between 10-16 volts.
The barometric pressure (BARO) is greater than 74 kPa.
No fuel filling during the EONV test period.
The fuel level is between 15-85 percent.
The start-up engine coolant temperature (ECT) and the start-up intake air temperature (IAT) are between
0-40°C (32-104°F).
The barometric pressure (BARO) is more than 74 kPa.
The engine run time before engine shut-off was greater than 10 minutes.
The drive distance before engine shut-off was more than 5 kilometers (3.1 miles).
The ignition is OFF.
The ambient air temperature at the end of the drive cycle is between 0-32°C (32-93°F).
DTC P0442 runs once per drive cycle during the hot soak period after the ignition is turned OFF and may
require up to 45 minutes to complete. The controller will not make more than 2 test attempts per day. The
time since the last completed EONV test must be at least 17 hours
CONDITIONS FOR SETTING THE DTC
The ECM detects a leak in the EVAP system that is greater than a calibrated amount.
The ECM must complete several EONV tests before the diagnostic can turn the MIL on or off.
2008 Chevrolet Silverado 1500
2008 ENGINE Engine Controls and Fuel - 4.3L - Sierra & Silverado
ACTION TAKEN WHEN THE DTC SETS
DTC P0442 is a Type A DTC.
CONDITIONS FOR CLEARING THE DTC
DTC P0442 is a Type A DTC.
DIAGNOSTIC AIDS
The EVAP system can be filled with smoke more quickly and completely by opening the system opposite
the end where the smoke is injected. When injecting smoke at the service port remove the fuel fill cap, or
temporarily leave the vent open, until smoke is observed then close the system and continue testing. If
using a fuel cap adapter at the filler neck, use the J 41413-VLV at the service port to allow the system to
fill faster. See Special Tools .
To help locate intermittent leaks using the J 41413-200 , move all EVAP components while observing
smoke with the J 41413-SPT . See Special Tools .
Individual components can be isolated and tested using adapters in the J 41413-300 .
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 parameter for vacuum decay.
P0454
DTC P0454 runs only when the engine-off natural vacuum small leak test, P0442, executes.
This test can run once per engine-off period. The length of the test can be up to 10 minutes.
A refueling event is not detected.
CONDITIONS FOR SETTING THE DTC
P0451
This DTC will set if the controller is unable to re-zero the FTP sensor voltage within a calibrated range during
the engine-off small leak test, P0442.
P0452
The FTP sensor voltage is less than 0.1 volt for more than 5 seconds.
P0453
The FTP sensor voltage is more than 4.9 volts for more than 5 seconds.
P0454
If, during the engine-off natural vacuum small leak test, P0442, the ECM detects an abrupt FTP signal change,
other than a refueling event, this DTC will set. An abrupt change is defined as a change of 0.45 inch H2O in the
span of 1 second.