P0499

Evaporative Emission System Vent Valve Control Circuit High

P0499 is a generic OBD-II powertrain diagnostic trouble code: Evaporative Emission System Vent Valve Control Circuit High. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0499
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
Need P0499 disabled?
RaceTune permanently disables any OBD-II trouble code on supported ECUs — for motorsport, off-road, and export use.
→

What P0499 means

P0499 is a generic emissions code for an electrical fault on the control circuit of the evaporative emission (EVAP) vent valve, where the voltage the ECU sees on that circuit is higher than expected. It is the counterpart to P0498 and it is an electrical code, not a leak code: the ECU is reporting the state of the wire that drives the valve, not whether the fuel vapour system is sealing.

The vent valve, also known as the canister close valve or canister vent solenoid, sits at the fresh-air inlet of the charcoal canister. It normally rests open so the fuel tank can breathe, and the ECU energises it to seal the system when it runs a leak test. The ECU drives the valve through an internal output stage and monitors the circuit each time it commands it. A high reading usually means the circuit is effectively open, so current never flows as intended, typically from a broken wire, an unplugged or corroded connector, or a solenoid coil that has failed open. A failed driver stage inside the module can also set it.

Because the valve is likely left in its default state, the vapour system may be unable to seal for testing. The visible results are a check engine light and an EVAP monitor that never completes, and depending on the vehicle there can be a fuel odour or refuelling complaints. The valve is mounted in a wet underbody location, so its connector and harness are the usual culprits.

Common causes

Most-frequently reported root causes when P0499 is logged.

  • 1
    A broken or corroded wire in the vent valve control circuit, leaving it electrically open.
  • 2
    An unplugged, loose or water-damaged connector at the vent valve, which sits exposed to road spray and salt.
  • 3
    A vent valve solenoid whose coil has failed open internally, so no current can pass.
  • 4
    Corroded or spread terminal pins that make intermittent contact and produce a fluctuating open-circuit reading.
  • 5
    Harness damage between the ECU and the valve from rodent chewing, exhaust heat or underbody impact.
  • 6
    A blown fuse or failed relay interrupting the supply side of the vent valve circuit.
  • 7
    A poor ground or reference connection shared by the vent valve circuit.
  • 8
    A failed output driver inside the engine control module, which is rare and should only be considered after the wiring is confirmed good.

Symptoms drivers notice

The check engine light is on, generally with no change in how the vehicle drives.
An occasional fuel vapour smell around the rear of the vehicle.
Difficulty filling the fuel tank to capacity, or the pump nozzle clicking off early on some vehicles.
The EVAP readiness monitor never completing, so the vehicle cannot be presented for an OBD test.
Minor driveability complaints such as a slightly unsteady idle if the vapour system cannot vent or purge normally.
Failure of an emissions inspection.

How to diagnose P0499

A typical diagnostic flow when this code is present.

  1. 1
    Record all stored codes and the freeze frame data, and note any other EVAP codes since one open circuit can set several related faults.
  2. 2
    Locate the vent valve at or near the charcoal canister and check first that its connector is fully seated, then inspect it for corrosion, water intrusion and spread or backed-out pins.
  3. 3
    Inspect the harness from the valve back towards the ECU for breaks, chafing, heat damage and rodent damage, flexing suspect sections by hand to expose intermittent opens.
  4. 4
    Check the fuse and any relay in the vent valve circuit, and confirm the circuit's ground or reference connection is clean and tight.
  5. 5
    Command the vent valve on and off with a scan tool while listening for the solenoid clicking, to establish whether the circuit is working at all.
  6. 6
    With the valve disconnected, test the control and supply wires for continuity back to the module, then check the solenoid winding for an open circuit against the manufacturer's specification.
  7. 7
    Only replace the vent valve or consider the control module once the connectors, harness continuity and grounds have all been proven good and the fault still follows the component.

Related powertrain codes

Frequently asked questions

Can I keep driving with P0499?

Yes, it is normally safe to keep driving. The fault is confined to the fuel vapour control system, which does not protect the engine or affect how power is delivered. The main downsides are the warning light, a possible fuel smell and the inevitable emissions test failure until it is repaired.

Will it fail an emissions test?

Yes. The check engine light is illuminated and the EVAP leak monitor is disabled while the circuit fault is present, so the vehicle fails both the OBD or visual inspection and the monitor readiness requirement.

What is the difference between P0499 and P0498?

They describe opposite electrical conditions on the same circuit. P0498 means the voltage was lower than expected, which usually points to a short to ground or a shorted solenoid. P0499 means the voltage was higher than expected, which usually points to an open circuit such as a broken wire, an unplugged connector or an open solenoid coil. The valve and wiring you inspect are the same in both cases.

Is this expensive to fix?

Generally no. The vent valve is an inexpensive part and much of the cost is labour to access it under the vehicle. If the actual problem is a broken or corroded section of harness, the parts cost is minimal but tracing and repairing the wiring properly takes some time.

Disabling P0499 in software

RaceTune can permanently disable P0499 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECU families we can disable P0499 on

We hold the DaVinci A2L disable definitions for these families, so the exact P0499 path and mask addresses are mapped. verified marks a confirmed disable definition. We support many more — upload your file and our identifier will match it automatically.

  • Bosch MG1CP002 verified

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

Got P0499 in your scan?

Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.

Upload your file