Technical Description of OBD-II Trouble Code
The circuit controlling the vent for the evaporative emission system vapor is experiencing a high level of control.
What does that mean?
This code is a generic powertrain code that applies to all makes and models of vehicles (1996-newer). However, the specific repair steps may vary depending on the model.
The Powertrain Control Module (PCM) / Engine Management Computer (EMC) / Engine Control Module (ECM) has detected a fault with the circuit that controls the vent for evaporative emission systems vapor.
As fuel sits in the tank, it releases fuel vapor. While driving, this vent opens and allows the vapors to be circulated into the engine intake manifold, a charcoal canister, or into the atmosphere, depending on the vehicle. This vent valve is part of the simple, yet complicated evaporative emissions system.
Symptoms
Symptoms of a P0499 DTC will include the illumination of the Malfunction Indicator Lamp (MIL), and you will likely not notice any other symptoms.
Causes
Potential causes may include:
Possible Solutions
Some steps to take to diagnose and repair this trouble code include the following:
Check your fuses, as there may be a fuse that powers the vent solenoid.
Check for a rubbed-through or chafed wiring harness. Check both wires to see if they are shorted to each other, to ground, or power.
Visually inspect the vent valve for cracks or damage.
Trace the wires to and from the PCM/EMC/ECM and check for continuity using a digital volt ohm meter (DVOM).
If you have access to an advanced level scan tool, actuate the valve while reading power and ground at the connector or by simply using a bulb wired to both terminals. It will light up if power and ground are OK.
Using a DVOM, check the resistance of the vent. In most cases, the resistance reading should be low. Refer to the manufacturer’s specification or compare it to a new one. Too high or low a value indicates a faulty coil inside the valve, meaning replacement is necessary. This code seems to be prevalent on Dodge, Chrysler, and Jeep products. In those cases, the vent valve was bad. With GM products (specifically pickups), GM has released a new updated valve assembly.
Finally, remove the valve. You may be able to access the pintle inside, and it simply could just be sticking from fuel residue. Clean it and retest.
