16 Electronic Variable Orifice (EVO) Fault

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Description

The electronic variable orifice (EVO) signal is pulse width modulated to control the power steering pressure/flow from the power steering pump. The PCM controls the ground and source voltage. When the vehicle speed is zero, current flow is zero milliamps. When vehicle speed reaches 19 KPH (12 MPH), current starts to flow and steering effort begins to increase.

Information Flag Parameters

Information Flag 16 will set if:

  • The PCM desired current does not match with feedback current.
  • In 1992 the fault must be present for 2.5 seconds before flag is set.

Diagnostic Aids

  • When the vehicle speed is zero MPH the current from the PCM will be zero milliamps (maximum power assist). Once the vehicle speed reaches 19 KPH (12 MPH) the current will gradually increase from 120 milliamps to 650 milliamps as the vehicle speed increases from 19 to 89 KPH (12 to 55 MPH). The increased current will provide decreasing amounts of power assist as speed increases.

NOTICE: Information Flags should be used for diagnostic purposes only. They do not necessarily indicate component malfunctions/failure.

  • Flag 16 may be set by loss of ignition when the vehicle is still moving. This is a normal condition.
  • The Scan Tool displays EVO output and feedback values to assist in EVO diagnosis. The two values have an inverse relation when output is 100% (at idle). Feedback should be at 0% and as vehicle speed increases above 19 KPH (12 MPH). Output should drop and feedback should rise indicating a good EVO subsystem.

IMPORTANT: The ignition must be cycled after a repair or Information Flag 16 will reset.