Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Monitor Description
5 hours after the ignition switch is turned to OFF, the electric vacuum pump creates negative pressure (vacuum) in the EVAP (Evaporative Emission) system. The ECM monitors for leaks and actuator malfunctions based on the EVAP pressure.
| Sequence | Operations | Descriptions | Duration |
|---|---|---|---|
| - | ECM activation | Activated by soak timer, 5 hours after ignition switch turned to OFF. | - |
| A | Atmospheric pressure measurement | Vent valve turned OFF (vent) and EVAP system pressure measured by ECM in order to register atmospheric pressure. If EVAP pressure does not reach between 70 kPa and 110 kPa (525 mmHg and 825 mmHg), ECM cancels EVAP system monitor. | 10 seconds |
| B | 0.02 inch leak pressure measurement | In order to determine 0.02 inch leak pressure standard, negative pressure (vacuum) created through 0.02 inch orifice and then EVAP system pressure measured by ECM. | 60 seconds |
| C | EVAP leak check | Vent valve turned ON (closed) to shut EVAP system. Negative pressure (vacuum) created in EVAP system, and EVAP system pressure then measured. If stabilized system pressure higher than 0.02 inch leak pressure standard, ECM determines that EVAP system leaking. If EVAP pressure does not stabilize within 12 minutes, ECM cancels EVAP system monitor. | 12 minutes* |
| D | Purge VSV monitor | Purge VSV opened and then EVAP system pressure measured by ECM. Large increase indicates normal. | 10 seconds |
| E | Final check | Atmospheric pressure measured and then monitoring result recorded by ECM. | - |
*If only a small amount of fuel is in the fuel tank, it takes longer for the EVAP pressure to stabilize.
- P2401: Vacuum pump stuck OFF
In operation B, the vacuum pump creates negative pressure (a vacuum) through the 0.02 inch orifice. The EVAP (Evaporative Emission) system pressure is then measured by the ECM, using the pressure sensor, to determine the 0.02 inch leak pressure standard. If the pressure is higher than -1.2 kPa (-9.0 mmHg)*, or lower than -4.3 kPa (-32.25 mmHg)*, the ECM interprets this as the vacuum pump being stuck OFF (not operating). The ECM illuminates the MIL and sets the DTC (2 trip detection logic).
*: The thresholds vary according to the atmospheric pressure measured in operation A. The values described above are based on an atmospheric pressure of 100 kPa (750.1 mmHg): absolute pressure.
- P2402: Vacuum pump stuck ON
In operation B, the vacuum pump creates negative pressure (a vacuum) through the 0.02 inch orifice. The EVAP (Evaporative Emission) system pressure is then measured by the ECM, using the pressure sensor, to determine the 0.02 inch leak pressure standard. If the pressure is higher than -1.2 kPa (-9.0 mmHg)*, or lower than -4.3 kPa (-32.25 mmHg)*, the ECM interprets this as the vacuum pump being stuck ON (remaining ON all the time). The ECM illuminates the MIL and sets the DTC (2 trip detection logic).
*: The thresholds vary according to the atmospheric pressure measured in operation A. The values described above are based on an atmospheric pressure of 100 kPa (750.1 mmHg): absolute pressure.
Fig 3: Evaporative Emission System Pressure Measuring Graphical Representation (Vacuum Pump Stuck On)Courtesy of TOYOTA MOTOR SALES, U.S.A., INC.
HINT:
The detection logic of DTCs P2401 and P2402 is the same because in both cases the 0.02 inch leak pressure standard measured in operation B is compared to the atmospheric pressure registered in operation A. The ECM calculates the difference between these pressures by deducting [the 0.02 inch leak pressure standard] from [the stored atmospheric pressure], and uses this to monitor the EVAP system pressure change.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.