P24B9: EVAP System Leak Detection Pump Pressure Sensor Circuit Range/Performance

P24B9 means the leak check module's pressure sensor delivers a signal that is electrically valid but not believable. GM's 2018 Volt table (ELCP) compares the absolute sensor reading with barometric pressure from the MAP sensor while pump and valve rest; a gap above 3,000 Pa at the engine-off wake-ups (roughly 4 to 11 h after shutdown) or above 15,000 to 20,000 Pa while driving counts as a fail, 50 of 63 samples, Type B. Mitsubishi's 2023 Outlander PHEV instead counts signal noise during the key-off test and fails after more than 20 fluctuations. FCA fixed P24B9 with PCM software on the 2017 Pacifica and the 2025 Grand Cherokee 4xe (18-079-25). P24BA and P24BB are the hard voltage limits.

Symptoms

• Malfunction indicator lamp on
• EVAP leak test aborted, readiness not set
• Usually no noticeable change in driving

Most likely causes

• Pressure sensor in the leak check module drifted or noisy
• Engine control software needing an update (FCA bulletins)
• Moisture or dirt in the module's pressure port
• Chafed wiring or loose pin causing signal disturbance

What to check, in order

Start with the simplest. You can tick off each step.

1. Start with the fuel cap: tighten it fully and check its seal
2. Compare the reading with other engine data while varying the engine speed.
3. Inspect the hoses and connections around the tank and the charcoal canister
4. Use the scanner to test the purge and vent solenoid valves
5. Run a smoke test to find small leaks

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P24B9 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 4: Emissions
• B9: Specific fault in that system

Frequently asked questions

Can I keep driving with code P24B9?

Yes, you can normally keep driving. If there is a strong smell of gasoline, find the leak before continuing and do not smoke nearby.

What causes code P24B9?

The most common causes are: pressure sensor in the leak check module drifted or noisy; engine control software needing an update (FCA bulletins); moisture or dirt in the module's pressure port.

Related codes

• P24B8EVAP System Leak Detection Pump Pressure Sensor Circuit
• P24BAEVAP System Leak Detection Pump Pressure Sensor Circuit Low
• P24BBEVAP System Leak Detection Pump Pressure Sensor Circuit High
• P24BCEVAP System Leak Detection Pump Pressure Sensor Circuit Intermittent
• P2404EVAP System Leak Detection Pump Sense Circuit Range/Performance
• P0451EVAP System Pressure Sensor/Switch A Circuit Range/Performance

Sources

• gsi.ext.gm.com: 18OBDG01 Hybrid Diagnostics
• mitsubishitechinfo.com: N502424270000800USA
• static.nhtsa.gov: MC 11022166 0001
• static.nhtsa.gov: MC 11017434 0001

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.