P24B8 is the general circuit fault of the pressure sensor that sits inside an evaporative leak check module together with the pump and the switching valve. The sensor gets a 5 V reference from the engine computer and reports canister-side pressure during the engine-off leak test. No manufacturer documents P24B8 publicly; GM, Mitsubishi and Subaru use the more specific P24B9 to P24BB for this sensor. CARB requires such EVAP input components to be checked for circuit faults and implausible values. With this fault present, the leak test cannot be trusted and will not complete, so the EVAP readiness flag stays open. Typical findings are a broken reference or ground wire, a corroded module plug or a failed module.
Low severity. Can I keep driving?Yes, you can normally keep driving. If there is a strong smell of gasoline, find the leak before continuing and do not smoke nearby.
Symptoms
- Malfunction indicator lamp on
- EVAP readiness monitor does not complete
Most likely causes
- Open or shorted 5 V reference, ground or signal wire to the leak check module
- Corroded or loose connector at the leak check module near the canister
- Pressure sensor inside the leak check module failed
- Engine control module does not supply the sensor reference
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P24B8 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 4: Emissions
- B8: Specific fault in that system
Frequently asked questions
Can I keep driving with code P24B8?
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 P24B8?
The most common causes are: open or shorted 5 V reference, ground or signal wire to the leak check module; corroded or loose connector at the leak check module near the canister; pressure sensor inside the leak check module failed.
Related codes
- P24B9EVAP System Leak Detection Pump Pressure Sensor Circuit Range/Performance
- 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
- P2400EVAP System Leak Detection Pump Control Circuit/Open
- P2403EVAP System Leak Detection Pump Sense Circuit/Open
Sources
- law.cornell.edu: 13 CCR 1968.2
- gsi.ext.gm.com: 18OBDG01 Hybrid Diagnostics
- mitsubishitechinfo.com: N502424280000800USA
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.