Hill Start Assist System is an excellent feature in modern Subaru cars. The system helps prevent vehicles from rolling backward when driving up a steep road. When driving up a hilly road, drivers release brake pressure occasionally, which is when your Subaru rolls backward.
The Hill Start Assist System keeps your Subaru from rolling backward by holding your brakes when switching between the brakes to the gas pedals. The system features a sensor that detects when you start going up a hilly road and brings the Hill Start Assist light on.
The system engages the brakes momentarily as you switch between the pedals. Once you press the gas pedal, it releases the brakes, and you can keep climbing the hill. This protects your Subaru from rolling down a hill when you are going up.
When driving up a steep road, your Electronic Control Unit illuminates the Hill Start Assist light to show that it has engaged the system, which goes off when the vehicle reaches a flat surface.
If there is a problem in the system, the Hill Start Assist System might remain on even when you are not climbing a hill. To understand what could be causing the light to stay on, let us highlight the components of the Hill Start Assist System.
Hill Start Assist Components
Your Subaru Hill Start Assist system has the following components.
Hill Start Assist system works with your Subaru’s computer system to activate the system when required. The electronic control unit, ECU, is a signal receptor that receives signals from different sensors within your vehicle. When driving up a steep road, the Hill Start Assist sensor transmits a signal to the ECU. The ECU then activates the system to assist you as you climb the hill road.
When the ECU receives a hill climb signal, it transmits it to the brake actuator, which remains on standby to activate the brakes until you finish climbing the hill road.
The angle sensor notifies your Subaru ECU that your vehicle is on an inclined road to engage the Hill Start Assist System.
Other components of the Hill Start Assist System include torque, pressure, and wheel speed sensors.
The torque sensor determines if the drivetrain sends enough torque to the wheels to accelerate through the inclined road. The pressure sensors work with the vehicle’s suspension system to determine the weight of your vehicle, including cargo and passenger weight. Pressure sensors transmit electrical signals in proportion to the weight of your Subaru.
The wheel-speed sensors determine the spinning speed and the direction your wheels turn. You will find these on the axles of your Subaru.
Reasons Your Subaru Hill Assist Light Stays On
The following are a few reasons why the Subaru Hill Start Assist light might stay on.
1) Špatné senzory
The Hill Start Assist system relies on several sensors to operate. These sensors include the angle sensor that detects when you start to climb a hill road, torque, pressure, and wheel-speed sensors. The angle sensor is the most critical sensor that could cause the Hill Start Assist Light to stay on.
When this sensor malfunctions, it can cause several problems for your Subaru. A faulty angle sensor may send incorrect data to the ECU or fail to send it. If your angle sensor fails, the Hill Start Assist light might stay on even when you are on flat ground or stay off even when climbing a hilly road.
Sensors may fail for several reasons, including dirt and debris, overheating, and faulty wiring.
2) Malfunctioning Wiring System
When your Hill Start Assist light stays on, it could be a malfunction in your wiring system. A wiring problem can affect several parts of your Hill Start Assist system, including the warning light. A defect in the electrical system can cause the light to remain on even when you are on a flat surface, cause it to remain off when climbing a hill road, or cause the light to illuminate sporadically.
This is a complicated problem to solve. You should try troubleshooting your Hill Start Assist Wiring system after you have checked every other area.
3) Electronic Control Unit Malfunction
Software and technical systems are not always the best. Although we depend on them very much, they can fail anytime.
Your Subaru Hill Start Assist System depends on the electronic control unit to function properly. The ECU depends on software to function. If the ECU software glitches, it affects the Hill Start Assist system and can cause the light to stay on.
If the ECU is the cause of your problems, you may notice other symptoms as follows.
- Kontrolka kontroly motoru se rozsvítí
If your ECU malfunctions, it may affect other areas, including the engine. The ECU manages the engine and its functions. It also reports any problem that may affect the functioning of the engine. When the ECU malfunctions, it may think other areas in your vehicle have malfunctioned, including the engine, illuminating the check engine light.
- Engine Hard Start or Stalling
The ECU is the command center of your vehicle; if it has a major malfunction, it may cause your vehicle to refuse to start or cause drivability issues. If your Hill Start Assist light refuses to go off and your vehicle has these symptoms, you should try troubleshooting the ECU.
4) Uneven Ground
The Hill Start Assist sensor detects when your Subaru steps on an inclined road and activates the system, bringing the Hill Start Assist light on. If you drive on uneven ground, the sensor may detect inclined surfaces and cause the light to come on. If the uneven ground stretches far, the light might stay on for as long as you are on that surface.
What to Do When Hill Start Assist Light Stays on
The Hill Start Assist light comes when your vehicle steps on an inclined road and goes out when you finish climbing and step on flat ground.
What happens if the light does not go off?
1) Use an OBD-II Scanner
When the Hill Start Assist light refuses to go off, it means there is a problem in the system. Scanning your vehicle’s ECU with an OBD-II scanner reveals the exact cause of the problem. You can use the scanner results to fix the problem causing the light to stay on.
2) Clean or Replace Sensors
Your Hill Start Assist system relies on several sensors to operate. If one of them fails, you can fix or replace it. For instance, if your sensor fails because of dirt and debris, you can clean it. If the failure is because of a problem with the wiring, you can use a decent multimeter to test and fix the electrical system of the sensor.
If the sensor is faulty and beyond cleaning and repair, you can replace it to fix the problem.
3) Update and Tune Your ECU
The ECU is the command center of your Subaru, an in-built computer that controls every sensor and chip in your vehicle. Like other computer systems, you must update your ECU’s operating system regularly.
If the operating system of your ECU is not up-to-date or the module malfunctions, it can wreak havoc on nearly every system that relies on it, including the Hill Start Assist system. To ensure your vehicle does not experience any problems because of a software update, keep your ECU up-to-date by checking your system for updates regularly.
Another way to keep your ECU running properly is by tuning it. When you tune your ECU, you optimize it to run more efficiently and powerfully. This ensures your ECU cannot malfunction and cause other systems like the Hill Start Assist to misbehave.
4) Replace the ECU
If, after all the diagnosis, you discover that your ECU is faulty beyond repair, you can replace it. However, for an ECU to be faulty to this extent, you will have to experience other problems to inform your decision to replace it.
If the plan is to replace the whole ECU unit, you will require a professional mechanic’s help purchasing the right model, programming, and installing it. The cost of replacing the electronic control unit will depend heavily on the model of your Subaru.
On average, you could pay at least $400 and $1,400 at most. The labor charges will range between $100 and $200. If your budget is a little tight, you can opt to purchase a remanufactured ECU, which, of course, comes with risks.
