P24D9: EVAP System Pressure Sensor or Switch B Circuit Intermittent

What it means

The EVAP system pressure sensor or switch B circuit has an intermittent or erratic signal. The code identifies a circuit signal problem; it does not by itself indicate an EVAP leak or a faulty purge valve.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The EVAP pressure sensor or switch B reports pressure changes in the fuel-vapour system to the control module. The module sets P24D9 when the signal on circuit B behaves erratically or cuts in and out, rather than tracking pressure consistently; this points to a circuit signal problem and does not alone confirm a leak.

Common causes

Most likely first.

1. Loose or corroded connector
2. Damaged wiring
3. Faulty pressure sensor or switch

Symptoms

• Check engine light on
• Possible smell of fuel near tank or engine bay
• Failed emissions inspection
• Loose-cap warning may appear

How to diagnose it

1. Use a scan tool to record freeze-frame data and watch the EVAP pressure reading for sudden dropouts or jumps.
2. Inspect the connector for sensor or switch B for looseness, corrosion, moisture, or damaged pins.
3. Trace the B circuit wiring for chafing, breaks, or damage, especially where movement or heat could make the fault intermittent.
4. With the wiring diagram, check circuit continuity and connections while gently flexing the harness to reproduce an intermittent fault.
5. If the circuit and connections are sound, test sensor or switch B against the manufacturer's specification.

Common fixes

• Reconnect and secure a loose connector at EVAP pressure sensor or switch B.
• Clean corroded connector contacts and repair damaged pins.
• Repair or replace damaged wiring in the B circuit.
• Replace sensor or switch B if it fails the specified test.

Can I keep driving?

If the vehicle runs normally and there is no fuel smell, short trips are generally reasonable, but arrange diagnosis soon because emissions monitoring may be impaired. If you smell fuel strongly or see a fuel leak, stop driving and address the leak promptly.