The code P0498: Evaporative Emission System Vent Valve Control Circuit Low points out a fault in the Evaporative Emission System Vent Valve Control Circuit, indicating that the voltage in the circuit is lower than expected. This could mean an electrical issue is preventing the vent valve from operating correctly, potentially affecting the vehicle’s emissions control and fuel efficiency.
P0498 quick overview
| Meaning | P0498: Evaporative Emission System Vent Valve Control Circuit Low |
| Is it serious? | This code indicates an issue with the EVAP system, which controls emissions and is important for fuel efficiency and preventing fuel vapor leaks, but it’s typically not an immediate breakdown risk. |
| Possible causes | – Faulty Canister Vent Valve – Damaged or disconnected wiring to the valve – Short or open in the vent valve control circuit – Faulty Powertrain Control Module (PCM) |
| How to diagnose? | Inspect Vent Valve: Check the canister vent valve for signs of damage or malfunction. Check Wiring and Connectors: Examine the valve’s wiring and connectors for damage or disconnection. Verify Power and Grounds: Ensure the valve circuit has the proper power supply and grounding. Test Valve Operation: Perform electrical tests on the vent valve to ensure it operates correctly. Look for Circuit Issues: Check for shorts or opens in the vent valve control circuit. Consider PCM Inspection: If other diagnostics are inconclusive, assess the PCM for faults. |
P0498 Meaning
The P0498 code means your car’s computer has detected a problem with a part of the emissions system that controls vapor from the fuel. This system helps reduce air pollution and maintain fuel efficiency. When this code is set, it usually means there’s an electrical issue in the part that releases these vapors. While it might not stop your car from running right away, it’s important to fix it to ensure your car runs efficiently and doesn’t pollute the air. The common steps to diagnose this involve checking the electrical parts and connections of the system.
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How to fix P0498 – learn from mechanics
I looked into P0498 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Honda
Vehicle Information:
2007 Honda Accord EX 3.0L
Issue + Repair History:
- Vehicle came in with P0498 & P0499 codes.
- Replaced the Vent Shut Valve and repaired a shady connection at the charcoal canister.
- Vehicle returned with the same codes.
Other OBD2 Codes + Test Results:
- P0498: Evap canister Vent shut valve circuit low voltage
- P0499: Evap canister Vent shut valve circuit high voltage
Suggestions to Fix Issue:
- Check if the car is still under warranty.
- Disconnect CVS circuit low voltage valve & measure resistance across terminals.
- Inspect for shorts between CVS circuit low voltage and ECM/PCM.
- Consider potential rodent damage or damage to the wiring harness or a bad PCM.
- Check connectors, A/F sensor relay, and wiring.
- Look for erratic ground or intermittent connection from the valve to the ECM.
- Replace the entire charcoal canister if necessary.
- Inspect the connections at connector C501 for poor connections.
Final Fix:
- Found that the car had been clipped in the rear, reversing 2 wires leading to the VSV valve.
- Wiring was repaired, and after concluding that the PCM was defective, the customer (used car dealer) took it to the dealer to get it covered under warranty.
Case #2: Chevrolet
Vehicle Information:
2008 Chevrolet Aveo LS 1.6L
Issue + Repair History:
- Car is not shifting and has no speedometer operation.
- Replaced output speed sensor with no change.
- No communication with TCM and has multiple codes including a hard code P0498.
Other OBD2 Codes + Test Results:
- P0455: EVAP system large leak.
- P0502: Vehicle speed sensor circuit.
- P0498: EVAP vent solenoid control circuit low voltage.
Suggestions to Fix Issue:
- Check ECM, TCM fuse F6 in the IP fuse block or terminal 1 at VSS for 12 volts.
- Verify that terminal 2 of VSS is ground and terminal 3 is the signal circuit with under 2 ohms to TCM connector B25.
- Consider potential issues with the ECM if the voltage is out of the specified range.
- Ensure the VSS is correctly torqued to the transmission housing.
- Check the low reference circuit and ground for less than 1 ohm of resistance.
- Test for 9-11 volts between the signal circuit and ground.
Final Fix:
- A blown fuse was discovered when following the advice to check the ECM and TCM fuse. Replacing the fuse resolved the issue.
Case #3: Honda
Vehicle Information:
2008 Honda Accord EX 3.5L
Issue + Repair History:
- Compressor clutch would engage for 3 seconds and then disengage when the check engine light comes on.
- Replaced output speed sensor with no change.
- Disconnecting the battery overnight didn’t help.
Other OBD2 Codes + Test Results:
- U0155: F-CAN malfunction (ECM/PCM-GUAGE control module).
- P0498: EVAP CVS circuit voltage low.
- P0453: EVAP FTP sensor high input.
Suggestions to Fix Issue:
- Try operating the vehicle with the EVAP devices unplugged, clear codes, and retry.
- Check which modules are communicating on the network and inspect the power and grounds for those modules.
- Address the communication error between the gauge control module and PCM as bus problems can set various codes.
- Unplug modules one at a time to find one that restores communication if necessary.
- Investigate FTP and CVS codes, as they might indicate wiring or component issues.
- Focus on the communication code, which may interfere with PCM communication and disable AC.
Final Fix:
- The problem was the instrument cluster. Diagnosing all other codes first led to discovering that the cluster had an internal problem.
- Once the instrument cluster was replaced, the AC worked fine.
Case #4: Audi
Vehicle Information:
2004 Audi A8 Quattro L 4.2L
Issue + Repair History:
- Car supposedly quit while moving to clean snow.
- Replaced timing belt, pulleys, and spark plugs, but the car still doesn’t start.
- Codes P2401 and P0498 present with no communication from TCM.
- No smell of fuel at the tailpipe indicating potential fuel delivery issues.
Other OBD2 Codes + Test Results:
- P2401: Emission detection pump control circuit low.
- P0498: Emission vent valve control circuit low.
Suggestions to Fix Issue:
- Check fuel pressure and ensure the fuel pump is operating correctly.
- Verify if there’s spark and if the ignition is being pulsed.
- Check for fuel injector pulse and engine compression.
- Inspect if spark plugs are wet with fuel now.
- Watch live data, especially the crankshaft revolutions to diagnose potential issues with the RPM sensor.
- Ensure all fuses and connections are secure, particularly for the ECM and TCM.
- Consider the possibility of an immobilizer issue and check for related warning lights.
- If necessary, use a more specialized scan tool like Ross-Tech for VW/Audi vehicles for deeper diagnostics.
Final Fix:
- Found that the main fuel pump in the driver’s side of the tank was locked up. Replaced the fuel pump which resolved the issue. The process involved working through both pump access holes.
Case #5: Dodge
Vehicle Information:
2004 Dodge Ram 1500 ST 5.7L
Issue + Repair History:
- Vehicle stalls intermittently, particularly when slowing down or coming to a stop.
- Experiences surges in RPM from about 2100 to 1700 and back up.
- Previously, the dealership replaced the ECM and cleaned the throttle body. The customer then had a crank sensor installed along with a tune-up, but the problem persisted.
Other OBD2 Codes + Test Results:
- P0498: Canister vent valve circuit low.
Suggestions to Fix Issue:
- Check for possible fuel pump issues and monitor fuel pressure.
- Disable the EGR valve if equipped and observe any changes.
- Confirm the transmission fluid level is at the full mark.
- Consider the possibility of clogged fuel filters, especially if the vehicle has two of them.
- Explore the Mode 6 data for any EGR failures on deceleration.
- Investigate for worn distributor shaft drive gear as per TSB 18-08-93.
- Track down any shorts in the wiring harness related to the vent valve code, as this could affect other circuits.
Final Fix:
- After replacing the throttle body and experiencing continued issues, the dealership replaced the PCM/engine wiring harness complete, which fixed the stall out issue.
- The EVAP code also cleared after the harness repair, suggesting the initial problem might have been a short in the harness affecting multiple systems.
How to diagnose P0498
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Advice | Brief Description of Diagnostic Step |
|---|---|
| Inspect Wiring and Connectors | Check the wiring and connectors for shorts, damage, or loose connections. |
| Verify Power and Grounds | Ensure the circuit has proper power supply and grounding. |
| Test the Canister Vent Valve | Perform tests on the canister vent valve to check for proper operation. |
| Replace Faulty Components | Consider replacing the canister vent valve if tests indicate it’s faulty. |
| Check for Shorts in the Harness | Look for any shorts in the wiring harness that may be causing the issue. |
| Examine Related Systems | Check related systems like the fuel pump and EGR for potential impacts. |
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko