DTC B1273 Lexus

Description

EVAPORATIVE SYSTEM OVERVIEW: The Powertrain Control Module (PCM) monitors the Evaporative Emission System operation. The two main areas being monitored are the integrity of the system against leaks and the ability of the system to get fuel vapor from the canister to the Intake Manifold. The basic strategy used is that in a sealed system, pressure will naturally increase or decrease in relation to temperature. As temperature increases, so does pressure inside the system. And conversely, as temperature decreases, vacuum is created if no leaks are present. The Evaporative System Integrity Monitor (ESIM) Switch has multiple functions. There are two weighted seals that keep the system normally closed from the atmosphere. The two weighted seals are used to regulate the system pressure between 250 Pa (+1 H2O) and -500 Pa (-2 H2O). There is also a vacuum actuated switch that closes when the vacuum reaches a calibrated value. During cooling, the internal weights seal the evaporative system from the atmosphere and allow the switch to close. If the switch closes it indicates that the system is not leaking. Only the ESIM Switch is used for leak check diagnostics. The Fuel Tank Pressure (FTP) Sensor is not used for diagnosing the system for small leak or large leak testing.