A power steering assist fault might not seem like the end of the world. In truth, it’s probably not compared to other things your car will go through.
However, you should still give it your full and immediate attention.
If your car’s suffering from a power steering assist fault, this article will tell you how to fix it. It will also walk you through how power steering works and why the issue will impact your car control.
Let’s get started.
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Bottom Line Up Front: Fixing Power Steering Assist Fault
In short: you’ll need to replace the specific component that’s broken. You might also need to top the hydraulic fluid up or have some in-depth ECU diagnosis.
Whatever the problem is, take it straight to a trusted mechanic for inspection. The car isn’t safe to drive.
What Is Power Steering?
Power steering is found in almost every modern car. The only exceptions might be certain devoted track-day models.
You might not think about it most of the time, but power steering is helping you. As in, a lot.
Without power steering, the steering wheel would be monumentally difficult to turn. Well, it’s far from impossible – people have managed it for decades – but it’s much more challenging than what you’re used to.
Power steering ‘assists’ you by increasing the amount of force on the steering rack. It essentially pushes in the same direction you’re turning.
There are two types of power steering systems: hydraulic and electric. The cause of the fault depends on which of these your car has.
How Hydraulic Power Steering Works
Hydraulic power steering works using power steering fluid. You’ll see this when you lift the hood. The reservoir cap often has a steering wheel icon or says “Power Steering Fluid”.
The hydraulic power steering fluid is pressurized by the power steering pump. It’s directed by the control valve. More on that in a moment.
The steering rack sits inside a cylindrical housing, along with several O-Rings and pressure regulators. It has a ring jutting out in the center. This seals against the cylinder and acts as a piston once the power steering pump and control valve start work.
The control valve, situated just before the pinion gear that connects to the rack, controls which side of the piston the hydraulic fluid is sent to.
For example, if it’s sent to the left side (and the right side isn’t pressurized), it’ll push the piston right. That’s what happens when you turn your steering wheel counter-clockwise to steer to the left.
The opposite is also true, of course.
How Electric Power Steering Works
Electric power steering (or EPS, also known as EPSA) works a little differently.
There are two types:
- Steering column-mounted EPS
- Rack-mounted EPS
Steering column-mounted EPS is used on light-duty vehicles such as small cars. If you have something a little larger, such as a truck or 4×4, you’re more likely to have rack-mounted EPS.
They each work based on the same principles.
When you turn the steering wheel, a torque sensor records how much effort you’re putting in. The ECU takes this reading and drives the EPS electric motor to “add” force to the steering rack.
The EPS motor can be mounted to the steering column or rack (hence the two types).
Crucially, the motor doesn’t stand in between anything mechanical. If it fails, you’ll lose power steering but should still be able to drive to a safe location.
One last thing. If your car has an electric power steering system, you won’t have any hydraulic fluid or pumps.
Symptoms Of Power Steering Assist Fault
When you see a power steering assist fault, you might notice the following symptoms:
- Warning light on the dashboard
- Difficulty turning the steering wheel (especially at low speeds)
- Vehicle pulling to one side when driving straight
- Unusual sounds (such as whining) while turning (hydraulic systems)
- Hydraulic fluid leaks visible under the car (hydraulic systems)
- A whining noise when you start the car (hydraulic systems)
- The steering wheel feels unusually light at high speeds (electric systems)
- Other electrical issues (signs of ECU failure – electric systems)
What Does ‘Power Steering Assist Fault’ Mean?
‘Power Steering Assist Fault’ means – as you might expect – there’s something wrong with your power steering system.
The exact fault could be anything in the power steering assist system.
Certain problems appear in hydraulic systems; others raise their heads in electric ones. Here are some of the most common culprits, organized by type.
Hydraulic Power Steering Assist Faults
Hydraulic power steering usually fails in one of two ways:
- Hydraulic fluid leak
- Power steering pump failure
It’s also possible, but uncommon, for the power steering control valve to stop working. This should only happen if dirt and debris somehow get into the fluid reservoir.
Hydraulic Fluid Leak
Hydraulic fluid leaks are pretty common. One of the regular culprits is the bushing and O-Ring sealing the hydraulic fluid into the cylinder and around the steering rack.
That said, leaks could come from anywhere. Worn down pipes, cracks, the control valve, and even the reservoir might drip and lose hydraulic fluid.
Usually, though, leaks stem from worn-out rubber seals.
Hydraulic fluid is a distinguishable red color. Don’t get it mixed up with brake fluid, although if that’s leaking, that’s an even more serious problem.
With a hydraulic fluid leak, there won’t be any fluid to assist you as you turn.
Power Steering Pump Failure
The power steering pump is driven by the engine’s serpentine drive belt. It pressurizes the hydraulic fluid, allowing the control valve to move it between the input and output lines.
It might not be the pump itself. Since the pump is driven by the belt, it or the respective pulley might have problems, too.
Without a power steering pump, there’s no hydraulic pressure. The control valve might still open, but there’s nothing to force the steering rack in either direction.
While you’ll still be able to drive, turning the steering wheel will require much more effort.
Electric Power Steering Assist Faults
There are three main components in the EPS system. Any of them could fail, but the electric motor is most likely.
- Electric motor failure
- Torque sensor problem
- ECU issue
Electric Motor Failure
The electric motor is responsible for adding torque to the steering column or rack. If it stops working, it won’t be assisting you.
The usual reason for EPS motor failure is overheating. It’s a motor, so this is always possible.
One of the most likely situations for the EPS motor to overheat is when you’re doing a lot of intense steering. Examples could include racing or going through a slalom at high speeds.
It could also fail more generically, of course. For instance, the bushes could wear out, or an electrical connection could rust.
Torque Sensor Problem
The torque sensor is responsible for recording how much turning force (“torque”) the driver puts through the steering wheel.
The ECU takes these readings and converts them into directions (if you like) for the motor.
The sensor might record too much/little torque. This could result in over- or under-assisting the steering. If the car registered this, it would display a power steering assist fault.
ECU Issue
The ECU receives raw data from the torque sensor. It then uses that data to power the motor.
The torque sensor information might be perfectly fine. However, if a fault is developing in the ECU, it might give the motor too much (or insufficient) power.
Is A Power Steering Assist Fault Serious?
A power steering assist fault should be immediately addressed. It isn’t as grave as, say, a head gasket failure, but it still needs looking at.
Put it this way: if you can see there’s a power steering assist fault, either from a warning light or the text appearing on your display, act.
Manufacturers don’t design cars to inform drivers of warnings just for fun. If it’s serious enough for the vehicle to need to warn you, it needs fixing.
The main danger of ignoring a power steering assist fault isn’t damage to your steering system. Rather, you’re more likely to run into issues with, well, crashing.
Without power steering, it’s much more challenging to maintain control of your vehicle. That’s why fixing it as soon as possible is paramount.
You can usually drive with a power steering assist fault unless it’s severely impacting your ability to drive safely. If in doubt, ring your mechanic and ask them, or book a call-out technician.
How To Fix Power Steering Assist Fault
Some want to know how to reset a power steering assist fault warning light. While you can always clear the codes with an OBD II code reader, you won’t actually fix the problem.
Don’t do this until the root problem has been solved and repaired. It’s best to leave it to a mechanic, anyway.
Here are a few pointers on how to fix a power steering assist fault.
In general, you’ll need to replace the affected part, swapping it out for a new one.
Also, don’t forget to check for any resultant damage done to the steering rack, as unlikely as it is.
Hydraulic Power Steering Fixes
- When you suffer a hydraulic fluid leak, it should be as simple as finding the leak and replacing the part. This usually involves new rubber seals but could be any power steering component.
- You’ll need a new part if your car has a power steering pump failure. The technician might also inspect the pulley and serpentine belt to ensure they work properly. This might cost around $500 to $600.
Electric Power Steering Fixes
- If the EPS electric motor fails, you usually need a new one. This requires disassembly of the steering column and switching in a new part. This should be around the same cost as a pump replacement – possibly a little more. Expect to pay $500 to $600.
- The same applies if the issue lies with your torque sensor. Mechanics will strip away the dashboard to expose the column. They’ll then switch the torque sensor for an OEM replacement. It should cost about the same as the motor, $500 to $600. If you have both done at the same time, it’ll be much less expensive.
- Unfortunately, ECU issues are very in-depth and, therefore, expensive – probably over $1,000. This isn’t something you can hope to fix yourself. If you need a new motor or torque sensor, you might need some minor ECU work to go along with it. Expect to pay $500 to $1,000 for this.
Rounding Up: Why To Fix Power Steering Assist Fault As Soon As Possible
If your car has a power steering assist fault, get it looked at and fixed as soon as possible.
Most power steering problems aren’t immediately dangerous. There are exceptions, though, especially with electric systems.
If you’re in doubt, take your car to a shop on a flatbed trailer. If necessary, you could also call a mechanic to your home or workplace.
Don’t take any chances. Get a power steering assist fault fixed as soon as you can.
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