The evaporative system includes the following components:
The EVAP purge solenoid valve allows manifold vacuum to purge the canister. The Powertrain Control Module (PCM) supplies a ground to energize the solenoid valve (purge ON). The EVAP purge solenoid control is Pulse Width Modulated (PWM) or turned ON and OFF several times a second. The duty cycle (pulse width) is determined by engine operating conditions including load, throttle position, coolant temperature and ambient temperature. The duty cycle is calculated by the PCM and the output is commanded when the appropriate conditions have been met.
The EVAP Vent solenoid is used to seal the EVAP system during the EVAP leak diagnostic tests. The fuel tank pressure sensor is used to monitor vacuum in the system during the diagnostic tests.
A stuck closed EVAP purge solenoid, stuck open EVAP vent solenoid, disconnected or damaged EVAP purge line or vent hose, leaking fuel cap, or fill neck should set a DTC P0440. A small leak in the EVAP system should set a DTC P0442. An EVAP vent solenoid stuck closed, a restricted vent hose, or a blocked EVAP canister should set a DTC P0446. A continuous purge condition with no purge commanded by the PCM (EVAP purge solenoid stuck open or leaking) should set a DTC P1441. Refer to the DTC tables for further diagnostic procedures regarding the EVAP system.
Check for the following conditions:
Important: Although these diagnostics are considered type A, they act like type B diagnostics under certain conditions. Whenever the EVAP diagnostics report that the system has passed, or if the battery has been disconnected, the diagnostic must fail during two consecutive cold start trips before setting a DTC. The initial failure is not reported to the diagnostic executive or displayed on a scan tool. A passing system always reports to the diagnostic executive immediately.
Number(s) below refer to the step number(s) on the Diagnostic Table.
The PCM will command the EVAP purge and EVAP canister vent valves closed with the scan tool Seal System EVAP output control function activated. Fuel tank pressure should not decrease under this condition.
The PCM commands the EVAP purge valve OFF (open) and the EVAP canister vent valve ON (closed) with the scan tool System Perf. EVAP output control function activated. Engine vacuum should cause fuel tank pressure to decrease when System Perf. is activated.
Step
Action
Value(s)
Yes
No
1
Was the Powertrain On-Board Diagnostic (OBD) System Check performed?
--
Go to Step 2
Go to Powertrain On Board Diagnostic (OBD) System Check
2
Is Fuel Tank Pressure at the specified value?
0 in. H2O
Go to Step 3
Go to DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage
3
Important:: Before continuing with diagnosis, zero the EVAP Pressure and Vacuum (inches of H2O) gauges on the (1)Main Valve (2)Evaporative Emission System Purge/Presure Diagnostic Station J 41413 (3)Nitrogen Cylinder (4)Black Connecting Hose (5)Threaded Fitting (6)Gauge Set EVAP pressure/purge diagnostic station (refer to tool operating instructions).
5 in. H2O
Go to Step 4
Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage
4
Monitor the EVAP Pressure gauge on the EVAP pressure/purge diagnostic station while commanding the EVAP canister vent valve OFF (Open).
Does EVAP Pressure decrease to the specified value within 5 seconds?
Go to Step 5
Go to DTC P0446 Evaporative Emission (EVAP) Vent System Performance
5
Is vacuum increasing to a value greater than the specified value?
Go to DTC P1441 Evaporative Emission (EVAP) System Flow During Non-Purge
Go to Step 6
6
Did vacuum increase to a value greater than the specified value?
-5 in H2O
System OK
Go to DTC P0440 Evaporative Emission (EVAP) System
