DTC P0496 (K20C1) (2017 2018)
DTC P0496: Evaporative Emission (EVAP) System High Purge Flow Detected
General Description
The evaporative emission (EVAP) system monitor detects leaks in the fuel supply system by inducing and utilizing negative pressure in engine idle and vehicle OFF (LOCK) mode. This monitor is also used for diagnosing both the EVAP canister purge valve and EVAP canister vent shut valve for rationality malfunctions. Fuel that evaporates from the fuel canister gets stored in the EVAP canister. The evaporated fuel trapped in the EVAP canister is occasionally flushed at the appropriate engine operating conditions into the intake manifold via the EVAP canister purge valve. The EVAP canister vent shut valve isolates the evaporative system from ambient air.
Canister purging (P2422)
The EVAP system monitor diagnostic starts with the canister purging. During canister purging, the fuel tank pressure is monitored against low rationality threshold. If the fuel tank pressure reaches the threshold, then the EVAP canister purge valve is commanded closed. If the fuel tank pressure remains below, this threshold for calibrated amount of time after EVAP canister purge valve has been closed, then the powertrain control module (PCM) detects as EVAP canister vent shut valve stuck closed (P2422). If an EVAP canister vent shut valve stuck closed (P2422) is detected, the EVAP system monitor will be aborted.
Conditioning: Pressure stabilization after purging
The EVAP system monitor continues with the closing of the EVAP canister purge valve. The pressure in the fuel tank system is initially lower than the ambient pressure immediately after canister purging. Closing the EVAP canister purge valve causes ambient air to rush into the fuel tank system via the open EVAP canister vent shut valve. This results in a rise in the fuel tank pressure. If the pressure in the fuel tank does not stabilize within a calibrated amount of time, the EVAP system monitor will be aborted.
Phase A: Compensation gradient determination
The EVAP system monitor continues with the closure of the EVAP canister vent shut valve (EVAP canister purge valve remains closed). The pressure in the fuel tank system may rise further due to fuel evaporation. The gradient of the pressure signal is monitored during a calibrated amount of time. EVAP system monitor will be aborted if the gradient exceeds a calibrated threshold - high fuel evaporation. In the event that excessive fuel evaporation is not detected, the compensation gradient will be stored at the end of the observation period (phase A). This compensation gradient will be used at a later time to correct the leak gradient that is measured in phase C.
On the other side, if the pressure in fuel tank falls down below a calibrated rationality threshold, an EVAP canister purge valve stuck open (P0496) will be detected. If an EVAP canister purge valve stuck open (P0496) is detected, the EVAP system monitor will be aborted.
Phase B: EVAP canister purge valve low flow monitor and detection of large leaks
Phase B starts with the opening of the EVAP canister purge valve. The resulting change in the EVAP system pressure (vacuum build up) is monitored by the fuel tank pressure (FTP) sensor. If the resulting pressure does not drop below a calibrated threshold after a calibrated amount of time, an EVAP canister purge valve stuck closed (P0497) will be detected.
In spite of a properly functioning EVAP canister purge valve, the fuel tank pressure can begin to drop but would not reach the calibrated differential pressure threshold. In this case, the continuous evaluation of the differential pressure gradient will be terminated after a calibrated amount of time has elapsed - timeout. A fault indicating a large leak will be set if the differential pressure gradient calculated during this vacuum build up time is less than a calibrated threshold. If the fuel tank pressure has reached the calibrated differential pressure threshold, then the vacuum build up process will be performed further till the fuel tank pressure decreases to the next calibrated differential pressure threshold for 0.02 inch leak test. If this leak test specific threshold has been not achieved within calibrated amount of time, an EVAP system large leak (P0455) will be detected. If an EVAP canister purge valve stuck closed (P0497) or an EVAP system large leak (P0455) is detected, the EVAP system monitor will be aborted.
Phase C: Detection of 0.04 inch and 0.02 inch leaks
The monitor proceeds with small leak detection (0.04 inch) only if a large leak has not been detected. Phase C begins with the closing of the EVAP canister purge valve. Since the canister ventilation valve is still closed, the ensuing rise in pressure resulting from vaporization should be equivalent to the previously stored compensation gradient in phase B. If the vacuum decay gradient in the fuel tank (rise in pressure) exceeds a calibrated threshold, an EVAP system small leak (P0442) will be detected. If an EVAP system small leak (P0442) is detected, the EVAP system monitor will be aborted.
The diagnostic threshold for the 0.02 inch monitor is lower when compared with the corresponding threshold for the 0.04 inch test. A flag indicating a leak suspicion will be set if the vacuum decay gradient in the fuel tank (rise in pressure) exceeds the calibrated threshold. It should be stressed that this leak suspicion must be confirmed by an ensuing engine off natural vacuum (EONV) test. The EONV test complements the 0.02 inch leak test of the EVAP system monitor. It is triggered when the EVAP system monitor runs and indicates a 0.02 inch leak may be present in the EVAP system or independently of EVAP system monitor after the vehicle OFF (LOCK) mode.
EONV test
The EONV test detects a small leak in the EVAP system by evaluating the changes in pressure that occur in the fuel system. Heat from a running engine and from the engine exhaust gas, as well as a rise in ambient temperature and pressure all contribute to an increase in fuel temperature. The temperature and pressure in the fuel tank momentarily rises even further when the vehicle is brought to a halt and its engine turned off. This is due to the sudden absence of the cooling effect of the ambient air that opposes the forward motion of the vehicle. Temperature fluctuations contribute to relatively large pressure changes in a leak free EVAP system and cause little pressure changes if there is leakage in the EVAP system.
Phase 1
Phase 1 is executed while the temperature is still rising. A rise in temperature will lead to an increase in pressure in a tight fuel system. Between phase 1 and phase 2, the EVAP canister vent shut valve opens for a calibrated amount of time bleeding off any residual pressure.
Phase 2
Phase 2 is executed only when the pressure built in phase 1 does not reach levels that are typical of a tight fuel system. Phase 2 monitors the vacuum built when the fuel temperature is decreasing. Little or no vacuum is built if there is leakage in the system. For a leak free system, the vacuum build will reach a threshold that is determined by the ambient temperature and the fuel tank level.
If the difference between the maximum differential pressure obtained in phase 1 and the minimum differential pressure obtained in phase 2 is less than the calibrated threshold, an EVAP system very small leak (P0456) will be detected.
Monitor Execution, Sequence, Duration, DTC Type
| Execution | Once per driving cycle |
| Sequence | None |
| Duration | - |
| DTC Type | Two drive cycles, MIL on |
Enable Conditions
| Condition | Minimum | Maximum |
|---|---|---|
| Elapsed time after starting the engine | 10 minutes | - |
| Elapsed time since the last canister purging | - | 30 seconds |
| Outside air temperature | 32 deg.F (0 deg.C) | 103.6 deg.F (39.8 deg.C) |
| Initial engine coolant temperature [ECT Sensor 1] | 32 deg.F (0 deg.C) | 103.6 deg.F (39.8 deg.C) |
| Barometric pressure [Baro Sensor] | 68 kPa (510 mmHg, 20.1 inHg) | - |
| Fuel tank pressure | -4 kPa (-30 mmHg, -1.1 inHg) | 4 kPa (30 mmHg, 1.1 inHg) |
| 12 volt battery voltage [Battery] | 10.7 V | 16 V |
| Fuel feedback | Closed loop | |
| Other | No refueling | |
| Both EVAP canister vent shut valve and EVAP canister purge valve are commanded open for at least 20 seconds | ||
[ ]: HDS Parameter
Malfunction Threshold
The difference between the fuel tank pressure and its reference (start) value during compensation gradient determination measurement is less than -0.175 kPa (-1.32 mmHg, -0.0517 inHg) within 4 seconds.
Possible Cause
NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
- EVAP canister purge valve open stuck
Confirmation Procedure
Operating Condition
- Start the engine and drive the vehicle for at least 10 minutes.
- Stop the vehicle and let it idle for 5 minutes.
- Turn the vehicle to the OFF (LOCK) mode and wait for a while (maximum 45 minutes).
- Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
With the HDS
None.
Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the MIL comes on and a Confirmed DTC and the freeze data are stored.
Conditions for clearing the DTC
The MIL is cleared if the malfunction does not return in three consecutive trips in which the diagnostic runs. The MIL, the Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command.