Low Circuit Value for Evaporative Emission System Vent Valve Control
What Does It Mean?
The Powertrain Control Module (PCM) / Engine Management Computer (EMC) / Engine Control Module (ECM) has detected a malfunction in the circuit that controls the vent for vapor in 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 P0498 will include the Malfunction Indicator Light (MIL) illuminating; you probably won’t notice any other symptoms.
Causes
Causes
Potential causes may include:
Faulty vent valve
Wire/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-ohmmeter (DVOM).
If you have access to an advanced-level scan tool, activate 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 reading that is too low or too high indicates a faulty coil inside the valve, meaning a replacement is necessary. This code seems to be common on Dodge, Chrysler, and Jeep products. In these cases, the vent valve was faulty. With GM products (especially trucks), GM has released a new updated valve assembly.
Finally, remove the valve; you may be able to access the pivot inside, and it might just be sticking due to fuel residue. Clean it and retest.