Diagnostic Overview - Electric Vacuum Pump (EVP) System

The PCM performs circuit fault detection on the Electric Vacuum Pump (EVP) Control circuitry and sets the P258A-ELECTRIC VACUUM PUMP CIRCUIT fault if an open or shorted condition is detected. The PCM cannot directly monitor the Electric Vacuum Pump Battery Supply or ground circuits. Instead, the PCM performs a system performance diagnostic. When the EVP Relay is energized the PCM monitors the Vacuum Pressure Sensor Signal input to make a determination if the Vacuum Pump is functional.  If the PCM does not see a change in vacuum for a calibrated period after the relay is energized, the diagnostic fails and the PCM sets the P258B-ELECTRIC VACUUM PUMP PERFORMANCE fault. The performance diagnostic will detect any issue that can affect vacuum in the system. There are several electrical and mechanical failures that could cause the diagnostic to fail.

• An electrical or mechanical failure with the vacuum pump or an issue with the vacuum pump circuits.
• A leaking Vacuum Brake Booster assembly.
• Leaking or damaged vacuum tubes or check valve.
• It's also possible for the system to be functioning properly but fail due to a Vacuum Pressure Sensor that is stuck in range and not changing.
  NOTE:

  It is possible in some cases for pressure sensors to stick mid range if the 5-Volt Supply is missing to the pressure sensor. This is dependant on the type of pressure sensor being used.