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Error Code P0498 is defined as Evaporative Emission System Vent Valve Control Circuit Low. This is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, particularly those made since 1996 up to present. Specifications on the definition, troubleshooting, and repairs may vary from one make and model to another.
The EVAP (evaporative emission control system) is designed to capture fuel vapor and keep them from escaping into the atmosphere by routing them to the engine where they can be burned later. Before getting to the engine though, vapors are stored in a closed reservoir (canister) until the engine is ready to burn them, through a specially designed valve and a network of metal tubes and rubber hoses. The pressure that is built when the fuel is stored causes the vapors to vent into the tubes, and eventually lead to the canister. This canister contains a charcoal element which absorbs fuel vapors, which will be released at the right time.
The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) monitors and controls the EVAP system, and commands the purge and vent valves to open. The engine intake vacuum creates a partial vacuum in the EVAP system, allowing fresh air to enter the valve, and simultaneously flushing out vapor to be burned.
If the PCM detects a problem in the EVAP system, particularly in the vent valve circuit indicating “low”, then the Error Code P0498 will be stored, and the Check Engine light will be activated.
Other related Error Codes include:
- Error Codes P0440 Evaporative Emission Control System Malfunction
- Error Codes P0443 Evaporative Emission Control System Purge Control Valve Circuit
- Error Codes P0444 Evaporative Emission Control System Purge Control Valve Circuit Open
- Error Codes P0445 Evaporative Emission Control System Purge Control Valve Circuit Shorted
- Error Codes P0446 Evaporative Emission Control System Vent Control Circuit Malfunction
- Error Codes P0447 Evaporative Emission Control System Vent Control Circuit Open
- Error Codes P0448 Evaporative Emission Control System Vent Control Circuit Shorted
- Error Codes P0449 Evaporative Emission Control System Vent Valve Circuit Malfunction
- Error Codes P0458 Evaporative Emission System Purge Control Valve Circuit Low
- Error Codes P0459 Evaporative Emission System Purge Control Valve Circuit High
- Error Codes P0499 Evaporative Emission System Vent Valve Control Circuit High
As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system.
- Slight increase in fuel consumption
- Slight engine performance loss
In most cases, however, there will be no noticeable symptoms.
Common possible causes for this error code include:
- Defective vent valve
- Issue in wire or circuit
- Defective PCM (rare)
How to Check
To diagnose this code, technicians use DVOM (digital volt-ohm meter), repair manuals, or electrical wiring diagram to evaluate the connection between the CCV (canister close valve) and the PCM. They start the diagnosis depending on which one component is more accessible.
For the PCM Side
Technicians will check the integrity of the overall circuit, including the CCV. They disconnect the PCM and test it for resistance across their appropriate terminals. Usually, solenoid valve measures 25 Ω and 35 Ω at room temperature. They would have to consult with the manual for the specific digits to determine the proper resistance of the specific vehicle.
While the PCM is disconnected, they will then check the ground for resistance on both power and ground sides of the CCV circuit. Both ends should have infinite grounds (open circuit) to ground.
If there is resistance higher than the specifications set by the manufacturer (40 Ω to ∞ Ω), then there may be a problem in the wiring, which could be a broken wire, corrosion, or defective CCV.
If the resistance is lower than the specifications set by the manufacturer (0 Ω to 20 Ω), then there’s a good chance there’s a damaged wire harness or also defective CCV.
This is why technicians will have to check the wiring harness and look for signs of chafed wires, as well as check the CCV for broken or bent pins, and corrosion, and repair as necessary.
For the CCV
Technicians will disconnect the CCV and measure the resistance across the terminals, between 25 Ω and 35 Ω at room temperature. If it’s outside the range, then the sensor must be replaced.
How to Fix
Common repairs for this code include:
- Repair or replacement of damaged or corroded wiring harness and wires
- Repair or replacement of cracked or damaged vent valve
- Cleaning the pintle off of fuel residue
Some Honda vehicles, such as Element, Civic, and Accord, have reported faulty vent shut valves, which results to this code. Replacing the defective component usually fixes the problem. However, always finish circuit diagnosis before condemning the valve itself.
Rodent damage is also a common cause for this code since the EVAP system is exposed, as nesting animals often cause damage to the wiring. Thus, make sure you also look for signs of nesting and animal droppings, which will likely point you in the direction of the fault.