Powertrain, generic (extended)

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

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

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

Symptoms

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

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–500
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

evap leak detection pump pressure sensor

Related codes

P24B8P24BAP24BBP24BCP2404P0451

References: gsi.ext.gm.com, mitsubishitechinfo.com, static.nhtsa.gov, static.nhtsa.gov.