Description

Purge Canister Closure Valve Description

1. Fault Codes:
Purge canister closure valve malfunction: P0446
Purge canister closure valve performance: P1447
2. Monitoring Procedure

Closure Valve PWM Drive Hardware Test
The diagnostic test samples Close Valve Diag PWM Buff Status to determine whether a fault has occurred, and if so a counter Close Valve Diag PWM Fault Cntr is incremented up, to a limit of Close Valve Diag PWM Fault Limit. If no fault event occurs, then decrement Close Valve Diag PWM Fault Cntr down to a limit of zero. If the count reaches the limit Close Valve Diag PWM Fault Limit then a purge canister closure valve open or short circuit fault is present.

Closure Valve Performance Test
The test compares the value of fuel tank pressure against a threshold, during normal purge operation. If the value of FUEL TANK PRESS VOLTS is less than CLOSE VALVE BLOCKED PRESS, then an appropriate fault counter is incremented up to a limit of close valve blocked diagnostic fault limit. Otherwise the fault counter is decremented down to a limit of zero. If the fault counter reaches the limit then a closure valve flow fault is present.

3. Primary Detection Parameter

Closure Valve PWM Drive Hardware Test
Hardware fault status from closure valve drive ASIC which monitors line voltage before low side drive transistor.

Closure Valve Performance Test
Fuel tank pressure - Measured in volts, the outcome of a potential divider calculation.

4. Fault Criteria Limits
Close Valve Diag PWM Fault Limit 50 samples
Close Valve Blocked Pressure -3.5 kPa
5. Monitoring Conditions
The Closure valve PWM drive hardware test occurs continuously.
The performance test will take place during normal purge operation.
6. Monitoring Time Length / Frequency of Checks
The frequency of the closure valve diagnostic is 10Hz.
7. Criteria for Storing Fault Code
Two successive trips where the diagnostic routines indicate a failed closure valve or closure valve circuit.
8. Criteria for Illuminating MIL
Two successive trips where the diagnostic routines indicate a failed closure valve or closure valve circuit.
9. Criteria for Determining Out of Range Input Signals
The hardware sampling technique monitors non-linear signals; the criteria will be signal/no signal.