High Value of the Evaporative Emission System Vent Valve Control Circuit
What Does It Mean?
This code is a generic powertrain code. It is considered generic because it applies to all makes and models of vehicles (1996-newer), although specific repair steps may vary by model.
The Powertrain Control Module (PCM) / Engine Management Computer (EMC) / Engine Control Module (ECM) has detected a failure in the circuit that controls the vent for the vapor from the evaporative emission systems.
When fuel is in the tank, it emits fuel vapor, while the vent line opens and allows the vapors to flow into the engine intake manifold, a charcoal canister, or into the atmosphere, depending on the vehicle. This purge valve is part of the simple yet complicated evaporative emissions system.
Symptoms
Symptoms of a DTC P0499 include the illumination of the Malfunction Indicator Light (MIL); you will likely not notice any other symptoms.
Causes
Potential causes may include:
Faulty vent valve
Wiring/circuit issue
PCM/EMC/ECM fault
Possible Solutions
Here are some steps to follow to diagnose and repair this fault code:
Check your fuses; there may be a fuse that powers the vent solenoid.
Look for a chafed or rubbed wiring harness. Check both wires to see if they are shorted to each other, to ground, or to 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 the power and ground at the connector or simply use a test light wired to both terminals; it will light up if the 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 specifications or compare it to a new one. A value that is too high or too low indicates a faulty coil inside the valve, meaning a replacement is necessary. This code appears to be widespread on Dodge, Chrysler, and Jeep products. In these cases, the vent valve was faulty. With GM products (especially trucks), GM has released an updated valve set.
Finally, remove the valve; you may be able to access the pivot inside, and it might simply be sticking due to fuel residue. Clean it and retest.