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P1555

Electronic Variable Orifice Output.

  • Buick
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
5
AreaVehicle speed, idle control and auxiliary inputs
55
FaultThe specific fault in that area

What it means

On Buick, P1555 means Electronic Variable Orifice Output. The EVO system adjusts power steering assist to suit vehicle speed. The control unit has seen a fault in the EVO actuator's output circuit, such as an open circuit, short circuit or a command that does not match the measured electrical state. How the system is laid out and which module drives it depends on the model and year.

Symptoms

  • Steering feels too heavy or too light at some speeds
  • Steering effort does not change smoothly as road speed rises
  • Power steering or service light on, depending on model
  • Fault code stored with no other obvious fault
  • Intermittent change in steering feel that may come and go with temperature or bumps

Possible causes

  • Faulty EVO actuator or solenoid (internal open or short circuit)likely
  • Damaged, chafed or corroded wiring to the actuatorlikely
  • Poor connection at the actuator or control unit connector (corrosion, loose or spread terminals)likely
  • Contaminated or low power steering fluid affecting the actuatorpossible
  • Blown fuse or fault in the power or ground supply to the circuitpossible
  • Fault in the control unit output driverrare

How to diagnose

  1. Read and record the freeze frame data and any other stored codes, then note whether P1555 returns after clearing.
  2. Check the power steering fluid level and condition, and look for leaks around the pump, rack and actuator.
  3. Visually inspect the wiring and connector at the EVO actuator for chafing, heat damage, corrosion and water ingress.
  4. Check the relevant fuse and the circuit's power and ground supplies against the wiring diagram for your model.
  5. Measure the actuator's resistance and compare it with the manufacturer's specification for your vehicle.
  6. With the wiring disconnected, test the circuit for continuity and for shorts to ground or voltage.
  7. Use a scan tool to command the actuator if supported, and check that the control unit's output responds.
  8. Check for any manufacturer service bulletins or calibration updates relevant to your model before condemning the control unit.

How to fix

  • Repair or replace damaged wiring and fix any short or open circuit found.
  • Clean or replace corroded or loose connector terminals and secure the connector.
  • Replace the EVO actuator if its resistance or operation is out of specification.
  • Correct the fluid level, or flush and refill with the specified fluid if it is contaminated, and fix any leaks.
  • Replace a blown fuse only after finding out why it failed.
  • Repair or replace the control unit only once the wiring and actuator have been proven good.

Can I keep driving?

Medium severity

The car can usually be driven carefully, but steering effort may be heavier or lighter than normal at some speeds, so allow extra room for manoeuvres. Have it checked soon, particularly if the steering feel is noticeably affected.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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