| Subject: | Evaporative Emissions DTC P0440, P0441, P0442, P0446 |
| Models: | 1996-2002 Passenger Cars and Trucks |
| With Enhanced Evaporative Emissions Engines |
| Except 1998-1999 Chevrolet Prizm |
This bulletin is being revised to add model years and diagnostic enhancements.
Please discard Corporate Bulletin Number 00-06-04-011 (Section
6-Engine).
Enhanced Evaporative Emissions testing of 1996 and newer vehicles with
enhanced evaporative emissions requires more stringent testing of the fuel
system for evaporative emissions leaks. Vehicles with this system use an on-board
diagnostic module (i.e. Powertrain Control Module (PCM) or Vehicle Control
Module (VCM) as the controller. For the balance of this bulletin, we will
refer to either of these components as a module.
Enhanced Evaporative Emission tests may be performed by the vehicle's
module when specific conditions are met. These conditions are determined by
the calibration within the module. These calibrations are vehicle platform
and engine family specific.
When the key is turned to the start or run position, the module checks
the output of various sensors on the vehicle to determine when and if the
Evaporative Emissions tests should be run. Refer to Engine Controls sub-section
of the appropriate Service Manual for specific DTC information.
Some of the most widely used parameters are listed below:
- The Barometric Pressure (BARO) is greater than a specified kPa
(psi).
- The system voltage is between 10 and 18 volts.
- The intake air temperature (IAT) is within specified temperature
values.
- The engine coolant temperature (ECT) is within specified temperature
values.
- The ECT and IAT are within specified temperatures of each other
when the vehicle engine was started.
- The fuel level sensor indicates the fuel level is greater than
a specified % of empty and less than a specified % of full. (For a 76 L
(20 gal) fuel tank, a fuel level of more than 11 L (3 gal)
but less than 64 L (17 gal) or as specified in the calibration).
- Some platforms such as the Alero and Grand Am, use a miles driven
check as well.
For the ECT and IAT to be within the specified temperatures of each
other at the time of engine start-up, the engine will have to be in the non-running
condition for a long enough period of time for the engine coolant temperature
to drop from its normal operating temperature down to roughly 30°C (90°F).
This could take several hours.
When the control module determines that the above conditions are met,
the module tests for a leak in the EVAP system by:
| • | Electrically closing the vent valve in order to seal the system. |
| • | Electrically opening the purge valve which allows the running
engine to draw a vacuum on the fuel tank. |
| • | The module then closes the purge valve, resealing the system. |
| • | The module then monitors the fuel tank pressure sensor and determines: |
| - | If vacuum was achieved. |
| - | If a leak is present, how large the leak is. |
| - | If vacuum was not achieved. |
| • | If one of the above tests fails, the module remembers that the
system failed the test. |
| • | If the module sees a failure of the EVAP test for two consecutive
tests, the module will set a trouble code for EVAP leak (DTCs P0440, P0442,
or P0446). |
Important: If the PCM is completing the EVAP diagnostic, filling of the fuel tank
cannot be completed as the vent valve will be closed and the fuel dispenser
nozzle will sense the pressure build-up and shut down. This is the expected
result. No parts should be replaced as nothing is faulty. To keep from encountering
this situation, it is imperative all customers and dealership personnel be
advised NOT TO FILL THE FUEL TANK WITH THE ENGINE RUNNING. If the condition
is encountered, turn the ignition to the OFF position for a minute. This will
allow the PCM to go to sleep completely, thereby opening the vent valve.
