Description

Fuel Evaporative System Monitoring Description

1. Fault Codes:
ELC system 1 fault P1496
ELC system 2 fault P1448
Purge valve stuck open P1440
Measure of leak test fault P0442
Purge valve circuit malfunction P0443

2. Monitoring Procedure

Measure Of Leak Test (Typical Operation):

When certain conditions are satisfied, the measurement of leak test is requested. This inhibits any other intrusive tests from being run.

The closure and purge valves are closed and the tank pressure is allowed to rise for a period of time during which the pressure is continuously sampled. The purge valve is then ramped open to evacuate the tank until the pressure falls below a preset threshold. If the threshold is not reached within a time limit, a system fault is flagged.

The purge valve is closed again. If the pressure rises above the threshold before the settle delay has elapsed, a leak is suspected; otherwise, the test is passed.

After the settle delay, the rising pressure is continuously sampled for the same period as in the first part of the test. An estimate of the size of the leak is calculated using data recorded in both parts of the test. If the result exceeds a threshold, a leak fault is flagged. To ensure that the tank is not subjected to excessive pressure or vacuum, the test is aborted if the tank pressure moves outside a band. The test is also aborted if filtered feedback for purge falls below a threshold during evacuation of the tank.

Purge Valve Stuck Open Test
The test compares the value of fuel tank pressure against a threshold. When the conditions for running the measure of leak test are valid and the closure valve is shut. If the value of fuel tank pressure is below the threshold, then a purge valve stuck open fault is present.

Purge Valve PWM Drive Hardware Test
The diagnostic test samples a Purge Diag PWM Buff Status to determine whether a fault has occurred, and if so a counter Purge Diag PWM Fault Cntr is incremented up, to a limit of
Purge Diag PWM Fault Limit.
Whenever Purge Diag PWM No Fault Limit consecutive no fault events occur, then decrement
Purge Diag PWM Fault Cntr down to a limit of zero.
If the count reaches Purge Diag PWM Fault Limit the limit then a purge valve open or short circuit fault is present.
3. Primary Detection Parameter
Measure of Leak Test
Fuel tank pressure
Purge Valve Stuck Open Test
Fuel tank pressure
Purge Valve PWM Drive Hardware Test
Hardware fault status from purge valve drive ASIC, which monitors line voltage before low side drive transistor.
4. Fault Criteria Limits
ELC System 1 Fault
ELC Diag Press Thresh +0.5kPa
ELC System 2 Fault
ELC Diag Press Thresh +0.5kPa
Measure of Leak Test Fault
ELC Diag MOL Thresh 50 (decimal)
Purge Valve PWM Drive Hardware Test
Purge Diag PWM Fault Limit 255 samples
Purge Valve Stuck Open
ELC Diag Over Vac Thresh -3.5kPa

5. Monitoring Conditions
The measure of leak test will not run (or shall abort) when the following faults or defaults are present:
- Multiple cylinder misfire fault
- Fuel tank pressure out of range
- Purge valve open or short circuit fault
- Any fuel level sensor fault
- Any oxygen sensor fault
- Any oxygen sensor heater fault
- Any air temperature fault
After a delay following the exit of cranking condition, the ELC diagnostic monitors for the following conditions to be true before the test is started:
- Manifold depression exceeds the ELC threshold
- Road speed within range
- Purge feedback adaption above the ELC purge adaption limit
- Closed loop fuelling is active on both banks
- Steady state conditions are present
- Fuel level within the ELC range
- OBD-II warm up conditions are satisfied
- Fuelling feed back is off clamp on both banks
- Fuelling feed back is not in default
- Air temperature is above the ELC limit
The Purge Valve PWM hardware test occurs continuously
6. Monitoring Time Length / Frequency of Checks
The Measure of Leak Test diagnostic runs at a frequency of once per trip.
The hardware test runs at 10Hz.
7. Criteria for Storing Fault Code
Two successive trips where the diagnostic routines indicate a fuel system leak or a failed purge valve or purge valve circuit.
8. Criteria for Illuminating MIL
Two successive trips where the diagnostic routines indicate a fuel system leak or a failed purge valve or purge 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.