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newSchoolWorks.com › VoTechWorks › Transportation › Automotive Technology › Steering and Suspension Systems › Lesson 8
TRN-AUTO19-04 · Lesson 8 · 16 clock hours · lab

Power Steering Service: Fluid, Pump, Hoses, and Electric Assist Calibration

Objective. Students will flush and refill a hydraulic power steering system, test pump pressure with a power steering analyzer, inspect and replace a high-pressure hose, and perform an EPS steering angle sensor reset procedure using a scan tool.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a certified examiner or master technician in the trade or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Power Steering Service: Fluid, Pump, Hoses, and Electric Assist Calibration

Power steering reduces the effort a driver needs to turn the wheel. Two main systems are in service today: hydraulic power steering (HPS) and electric power steering (EPS). A technician must be comfortable servicing both, because both appear on ASE A4 (Steering and Suspension) exam content and on vehicles you will see every day in the shop.

Hydraulic Power Steering: How It Works

An HPS system uses a belt-driven vane pump to pressurize power steering fluid. The pressurized fluid acts on a piston or a rack-and-pinion gear to reduce steering effort. A control valve, built into the steering gear, directs fluid to one side or the other based on wheel position. Fluid returns to a reservoir after passing through the gear. A pressure-relief valve inside the pump limits maximum system pressure so components are not damaged during hard stops against the steering lock.

Fluid Condition and Type

Power steering fluid degrades over time. Heat breaks down the additive package, and moisture contamination causes corrosion inside the pump and gear. Dark brown or black fluid, a burnt smell, or visible particles are all signs that a flush is needed. Always use the OEM-specified fluid type. Some vehicles require Dexron ATF; others require a manufacturer-specific fluid such as Honda PSF or GM's power steering fluid. Mixing incompatible fluids can swell seals and cause leaks. The correct fluid type is stamped on the reservoir cap or listed in the OEM service manual.

Flush procedure (turkey baster method):

1. Place drain pans under the vehicle.

2. Use a turkey baster to remove as much old fluid from the reservoir as possible.

3. Refill the reservoir with fresh, correct-specification fluid.

4. Start the engine and turn the wheel lock-to-lock several times to circulate new fluid through the system.

5. Repeat Steps 2–4 until fluid drawn from the reservoir is clean and meets OEM color expectations.

6. Check for leaks at all fittings and hose connections before returning the vehicle.

Hose Inspection and Replacement

Hydraulic power steering systems use two types of hoses: a high-pressure hose from the pump to the steering gear, and a low-pressure return hose from the gear back to the reservoir. The high-pressure hose is reinforced and rated for system pressure; the return hose operates at much lower pressure.

Inspect hoses for cracking, chafing, swelling, seeping fluid, or crimped sections. A hose that shows external cracks has an aged inner liner that may be flaking debris into the system. When replacing a high-pressure hose, use only the OEM-specified replacement or an equivalent-rated aftermarket hose. After installation, torque fittings to specification (see the OEM service manual), refill the reservoir, bleed the system by cycling the wheel lock-to-lock, and recheck for leaks.

Safety: Wear safety glasses and nitrile gloves when working with power steering fluid. High-pressure fluid escaping a pinhole can penetrate skin — treat any injection injury as a medical emergency and seek care immediately. Keep the engine OFF and system depressurized before loosening any high-pressure fittings.

Power Steering Pump Pressure and Flow Test

A power steering analyzer is a gauge set with an inline shutoff valve and a flow meter. It is installed between the pump outlet and the high-pressure hose to measure both pressure and flow. This test identifies whether a loss of power assist is caused by a worn pump or a leaking/binding steering gear.

Test procedure:

1. Install the analyzer with the shutoff valve fully open.

2. Start the engine and allow the fluid to reach normal operating temperature.

3. Record idle pressure with the wheels straight — this is the baseline relief pressure.

4. Slowly close the shutoff valve for no more than 10 seconds while reading maximum pressure. Do not hold the valve closed longer than 10 seconds or you will damage the pump.

5. If maximum pressure meets specification, the pump is serviceable. If it is significantly below specification, the pump is worn.

6. Note flow rate; low flow with adequate pressure may indicate a restriction.

Compare all readings to the OEM specification found in the service manual. Record actual values on the repair order.

Electric Power Steering: System Overview

EPS eliminates the hydraulic pump and fluid entirely. An electric motor — mounted on the steering column, rack, or pinion — provides assist based on signals from a torque sensor and a steering angle sensor (SAS). A dedicated EPS control module reads these inputs and commands the motor.

Because the SAS supplies data to the EPS module, the stability control system (ESC), and the advanced driver-assistance systems (ADAS), it must be calibrated any time the steering system is disassembled, a wheel alignment is performed, or the module or sensor is replaced.

Steering Angle Sensor Reset Procedure

The SAS reset is performed with a bidirectional-capable professional scan tool. The procedure varies by vehicle make and model, so always follow the on-screen prompts and the OEM procedure.

General SAS reset steps:

1. Connect the scan tool and verify communication with the EPS or ESC module.

2. Drive the vehicle (or use the guided procedure) to center the steering wheel.

3. Navigate to the SAS or EPS calibration function in the scan tool menu.

4. Follow all on-screen instructions — typically this involves holding the wheel straight and pressing a start button.

5. After the procedure completes, check for any stored DTCs related to the steering angle sensor or EPS system. A successful reset will show no related codes.

6. Document the procedure and result on the repair order.

Safety: During EPS calibration, the steering motor may move unexpectedly. Keep hands clear of the steering wheel spokes and ensure the vehicle is in PARK with the parking brake set.

Shop Safety Reminders

Key terms8

Hydraulic Power Steering (HPS)A steering assist system that uses a belt-driven pump to pressurize fluid, which acts on the steering gear to reduce driver effort.
Electric Power Steering (EPS)A steering assist system that uses an electric motor rather than hydraulic fluid to provide steering assist, controlled by an electronic module.
Power Steering AnalyzerA test instrument with an inline pressure gauge, shutoff valve, and flow meter installed between the pump outlet and steering gear to measure pump output pressure and flow.
Steering Angle Sensor (SAS)A sensor that measures the rotational position of the steering wheel and supplies this data to the EPS module, ESC system, and ADAS features; must be calibrated after steering system service.
High-Pressure HoseThe reinforced hose that carries pressurized fluid from the power steering pump to the steering gear; rated to withstand full system pressure.
Pressure-Relief ValveA valve inside the power steering pump that limits maximum system pressure to prevent damage to the pump, hoses, and steering gear.
Bidirectional Scan ToolA professional-grade scan tool capable of both reading vehicle data and sending commands to vehicle modules, enabling functions such as SAS reset and actuator tests.
Diagnostic Trouble Code (DTC)A fault code stored by a vehicle's electronic control module when a sensor reading or system function falls outside the expected range.

Worked examples4

1. A power steering analyzer shows idle pressure of 80 psi with the shutoff valve open. The OEM specification for idle pressure is 50–100 psi. When the technician slowly closes the shutoff valve, maximum pressure reads 1,050 psi. OEM maximum pressure specification is 1,100–1,300 psi. What does this result indicate?
  1. Step 1 – Evaluate idle pressure: 80 psi falls within the specified range of 50–100 psi, so the pump is building adequate baseline pressure.
  2. Step 2 – Evaluate maximum pressure: 1,050 psi is below the OEM minimum of 1,100 psi.
  3. Step 3 – Interpret the result: Maximum pressure below specification with the valve closed indicates the pump's internal vanes or pressure-relief valve are worn and the pump cannot achieve full pressure.
Answer: The pump is worn and should be replaced; it cannot reach the minimum required maximum pressure of 1,100 psi.
2. A technician performs a turkey baster flush. The reservoir holds approximately 1 pint. After the first extraction and refill, the fluid is 60% old and 40% new. After a second identical extraction and refill, approximately what percentage of the fluid in the reservoir is old fluid?
  1. Step 1 – After the first refill, the reservoir contains 60% old fluid.
  2. Step 2 – The turkey baster removes roughly the full reservoir volume each time, so the second extraction removes 60% old fluid along with 40% new fluid, leaving the reservoir empty.
  3. Step 3 – After refilling with 100% new fluid, the reservoir now contains 0% old fluid from this step — but the system (gear, hoses) still holds old fluid. However, if only the reservoir is considered: after two full extractions and refills of the reservoir itself, approximately (0.6 × 0.6) = 0.36, or 36% of the reservoir fluid is old.
  4. Step 4 – Calculate: 0.60 (old fraction after first flush) × 0.60 (fraction that was old, carried into second fill) = 0.36 = 36% old fluid remaining in the reservoir after two cycles.
Answer: Approximately 36% of the reservoir fluid is still old after two extraction-and-refill cycles, showing why multiple cycles and lock-to-lock steering are needed to fully flush the system.
3. A high-pressure hose fitting specifies a torque of 20 ft-lb. A technician's torque wrench reads in newton-meters (N·m). What torque value should the technician set on the wrench? (Use the conversion: 1 ft-lb = 1.356 N·m.)
  1. Step 1 – Write the conversion: target torque (N·m) = specified torque (ft-lb) × 1.356 N·m per ft-lb.
  2. Step 2 – Multiply: 20 ft-lb × 1.356 N·m/ft-lb = 27.12 N·m.
  3. Step 3 – Round to a practical value: 27 N·m.
Answer: The technician should set the torque wrench to approximately 27 N·m.
4. After an EPS scan tool calibration, the technician checks for DTCs and finds code C0051 (Steering Angle Sensor Circuit) still active. What is the most likely cause, and what should the technician do next?
  1. Step 1 – A DTC remaining after calibration means the SAS reset did not complete successfully or the sensor has a wiring or mechanical fault.
  2. Step 2 – Verify that the steering wheel was centered correctly during the calibration procedure, as an off-center wheel is a common reason the reset fails.
  3. Step 3 – Check the SAS wiring harness and connector for damage, corrosion, or loose pins.
  4. Step 4 – If wiring and centering are correct, inspect the sensor itself for damage; consult the OEM service manual for further diagnostic steps before repeating the calibration.
Answer: The calibration did not complete; the technician should verify the steering wheel was centered, inspect the SAS wiring, and follow OEM diagnostic steps before attempting the reset again.

The math in this lesson2

Learners convert hose fitting torque from ft-lb to N·m.
N-Q.1F-LE.2
Brush up in the math halls at newSchoolWorks.com:
In class: Students flush hydraulic power steering fluid from two shop vehicles using a turkey baster and fresh fluid method, check hose condition for cracking and leaks, and document fluid type and condition on a repair order. · Instructor demonstrates power steering pump pressure and flow test with a power steering analyzer (pressure gauge with shutoff valve); students perform the test on an assigned vehicle and compare readings to specification. · Using a professional scan tool, students navigate to the EPS calibration menu on a vehicle with electric power steering, perform the steering angle sensor (SAS) reset procedure following the on-screen prompts, and document the procedure and result.
Materials: Power steering pressure/flow analyzer, turkey baster, drain pans, power steering fluid (correct OEM type), high-pressure hose replacement and fittings, professional scan tool (bidirectional capable), shop towels, OEM service manuals, repair order forms
Check: Pressure test readings recorded and compared to specification on the repair order; SAS reset confirmed with scan tool showing no related DTCs after procedure — instructor reviews both documents and requires values within specification to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

A4 Steering and Suspension
1. A technician is preparing to flush hydraulic power steering fluid using the turkey baster method. Which action must be completed FIRST?
A4 Steering and Suspension
2. During a power steering pump pressure test with an analyzer, the technician closes the shutoff valve and holds it closed for 25 seconds to get a stable reading. What is the likely result of this action?
A4 Steering and Suspension
3. A power steering analyzer is installed on a vehicle. With the shutoff valve open and the engine at idle, system pressure is 75 psi. When the valve is slowly closed, maximum pressure only reaches 900 psi against a specification of 1,100–1,300 psi. What does this result most likely indicate?
A4 Steering and Suspension
4. A technician inspects a high-pressure power steering hose and finds visible cracks in the outer rubber jacket but no active leak. What is the correct action?
A4 Steering and Suspension
5. Which of the following scan tool capabilities is REQUIRED to perform an electric power steering steering angle sensor reset?
A4 Steering and Suspension
6. After completing an EPS steering angle sensor reset, what is the final verification step a technician should perform?
A4 Steering and Suspension
7. A customer complains of heavy steering effort on a vehicle with hydraulic power steering. The power steering fluid reservoir is full of dark brown fluid with a burnt smell. The MOST appropriate initial repair recommendation is to:
A4 Steering and Suspension
8. A technician replaces a high-pressure power steering hose and torques the fitting to 20 ft-lb as specified. Converting this value, approximately how many newton-meters is 20 ft-lb? (1 ft-lb = 1.356 N·m)
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