P0499 - EVAPORATIVE EMISSION SYSTEM VENT VALVE CONTROL CIRCUIT HIGH

DTC P0499 OBDII denotes that the PCM (Powertrain Control Module) has encountered pressure in the Evaporative Emissions Control System (EVAP), which exceeds the limit set by the manufacturer.

The EVAP system limits vapors from escaping into the atmosphere. Sometimes this system opens the purge valve which draws in fresh air needed by itself. If the EVAP System has not prescribed a purge condition and senses that there is a high-voltage pressure, which should not be there during this no-purge condition. This will establish that there is a malfunction in the EVAP System’s vent valve or its control circuit.

• Check Engine light illumination.
• Other emission system codes stored.

The reasons for setting the P0499 OBD2 fault code are:

• The purge control valve may be defective.
• The EVAP System canister valve may be damaged.
• The charcoal canister may be clogged.
• The charcoal canister may have fractures.
• Cracks in the steam hoses.
• EVAP Pressure Sensor may be defective.

To properly troubleshoot the P0499 OBDII diagnostic code you should consider the following:

• Inspect the fuel cap. It may not be installed correctly or it may be defective. If necessary, it should be replaced.
• Replace the solenoid or purge control valve.
• Replace the vent valve on the EVAP System canister.
• Clean the charcoal canister. If you find that the canister is damaged, you should replace it.
• Inspect the vacuum hoses. If they show cracks, replace them.
• Replace the EVAP Pressure Sensor.
• Using the DVOM, check the resistance of the vent orifice; in most cases, the resistance reading should be low, refer to the manufacturer's specifications or compare it to a new one. A value too high or too low indicates a malfunction of the coil inside the valve and therefore requires replacement.
• This code seems to be prevalent on Dodge, Chrysler, and Jeep products. In those cases, the exhaust valve was faulty. In terms of GM products (pickups in particular), GM has released a newly updated valve assembly.
• Finally, remove the valve, you can access the stem inside and it may stick to the remaining fuel. Clean it and repeat the test.