P0499 Code: Meaning, Symptoms, Causes & Fix

Overview

Symptoms

• increased fuel consumption
• check engine light
• rough idle under load

Common causes

• Broken terminal inside harness affecting evaporative emission system vent control circuit high
• Open circuit in wiring
• Connector pin damage/corrosion or harness stress near related components

How to diagnose P0499

1. Confirm P0499 and capture freeze-frame data with a professional scan tool.
2. Inspect wiring, connectors, and grounds related to evaporative emission system vent control circuit high for obvious defects.
3. Use a continuity test from module pin to component to identify opens/high resistance.
4. Check for related DTCs to identify the root-cause chain before replacing parts.
5. After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code P0499

Moderate: This code is moderate severity: the vehicle may still operate, but fault progression can increase repair cost over time.

Can you drive with P0499?

Most vehicles can be driven short-term with P0499, but postpone heavy load/highway driving until repaired.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

1. Repair obvious wiring/connector faults first to prevent repeat parts replacement.
2. Address the root fault mode (open) in the evaporative emission system vent control circuit high circuit/system.
3. Apply the required relearn/adaptation procedure if specified by service information.
4. Road-test and verify P0499 remains cleared under the conditions that originally set the code.

Fix options

• Clear corrosion and protect terminals.
• Restore continuity and verify pin tension.
• Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$180-$900

Common mistakes when diagnosing P0499

• Replacing parts without verifying voltage, ground, and signal integrity first.
• Ignoring related stored/pending codes that indicate upstream faults.
• Skipping post-repair verification drive cycle and readiness checks.

P0499 in common vehicles

P0499 appears across makes such as Ford, Toyota, Honda, Chevrolet. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes P0499?

P0499 is commonly set by open faults affecting evaporative emission system vent control circuit high.

How much does it cost to fix P0499?

For P0499, repair costs are typically $180-$900 depending on exact root cause, labor rates, and part quality.

Can I clear P0499 without repair?

You can clear P0499 temporarily, but the code usually returns until the underlying fault is corrected.

Helpful tools

• Estimate repair cost
• Decode your VIN
• Calculate fuel cost