A start-stop feature that fails to activate at the traffic light or when the car is idle can be annoying. After all, this innovation is designed to boost fuel efficiency and cut emissions — but only if it works!
If you’re asking yourself, “Why is my auto start-stop not working?”, you’re not alone!
Sometimes, an open driver door or a faulty accelerator pedal sensor can stop this feature from engaging.
Still facing this issue?
Let’s dive into other potential reasons your start-stop system might deactivate and explore the steps to restart it.
This Article Contains:
- Why Is Your Auto Start-Stop Not Working?
- How to Diagnose a Malfunctioning Auto Start-Stop System
- 9 Essential Repairs to Get Your Start-Stop System to Work
- What Are the Pros and Cons of an Auto Stop-Start System?
- Should You Manually Disable the Start-Stop System?
Why Is Your Auto Start-Stop Not Working?
The auto start-stop feature usually doesn’t activate if the seat belt is unfastened and the driver door is open. However, certain malfunctioning components can also prevent the feature from engaging.
Here are some prominent causes that may be stopping your system from doing its job:
1. Faulty Car Battery and Alternator
Cars with auto start-stop systems usually have a powerful Absorbent Glass Mat (AGM) or Enhanced Flooded Battery (EFB) unit. These batteries must have at least 70% charge to activate the start-stop feature. So, if your EFB or AGM battery has a low charge, the feature won’t work.
A battery may lose its charge if it’s too old, has corroded terminals, or loose cables. It may also die prematurely if a faulty alternator fails to charge it.
2. Malfunctioning Sensors
Modern vehicles use several sensors, including clutch pedal, vehicle speed, and accelerator pedal sensors, to engage the start-stop system. If any of these sensors have a wiring issue, the system won’t engage. You’ll also notice that your car’s fuel economy will slowly drop.
3. Inconsistent Engine Temperature
The auto start-stop system works best when the engine is at its normal operating temperature — usually around 190° to 225°F.
If the engine temperature is low because of cold weather or too high because of car overheating, the feature won’t engage. This prevents further damage to the internal components.
4. Use of the HVAC System in Extreme Climates
The start-stop function normally turns off your engine at a traffic light to reduce fuel consumption. But, during hot or cold weather, it doesn’t engage to ensure your HVAC system can function continuously.
Here’s why:
If you want to sit on comfy heated seats in cold weather, the engine has to run consistently to warm them. In this situation, the start-stop feature doesn’t activate even if the car is at the stop light.
Similarly, the feature will remain disengaged when the air conditioning system is at its highest setting during summer to ensure the cabin stays cool.
5. Outdated Control Module with Software Glitches
The power control module uses the brake pedal sensor, transmission system, and other components to engage the auto start-stop feature.
However, if the module is outdated or has software glitches, it won’t engage the system as it should.
6. Driving Conditions
Frequently driving in stop-and-go traffic can eventually cause the start-stop system to malfunction.
The constant stopping and restarting of the engine can put additional strain on your EFB or AGM battery, causing it to drain quickly. As the car battery drains, your start-stop system may cease to function altogether.
7. Steep Road Conditions
If you drive on a steep road, your car’s auto start-stop feature will disable automatically and activate Hill Start Assist (HSA). This system ensures a smooth uphill drive by preventing rollback when you transition from braking to accelerating.
Without HSA, a start-stop system can pose significant risks. When the engine restarts after a brief stop, the car might not have enough power to move forward, potentially rolling backward instead. This dangerous situation could lead to collisions with vehicles behind you.
To prioritize safety and give you 100% control, the start-stop feature is disabled as soon as the HSA system’s inclination sensors detect you’re driving at a steep angle.
NOTE: HSA is primarily available in mid-range and high-end car models, so if your vehicle doesn’t have it, it’s best to switch off the start-stop feature.
8. Steering Wheel Angle
When parking or reversing the car, you turn the steering wheel at a particular angle to guide the vehicle. In such a case, the start-stop system will detect the steering wheel angle, transmission mode (e.g., reverse gear), or other factors and disable itself automatically. This will offer you complete control over your vehicle’s movement.
Now that we’ve explored why your start-stop system may stop working, let’s check out the steps you can take to identify the root problem.
How to Diagnose a Malfunctioning Auto Start–Stop System
Inspecting start-stop systems can be tricky, as multiple parts could be causing the problem. It would be best to call a mechanic for thorough troubleshooting.
Here’s what they’ll do:
- Connect the OBD-II scanner to check whether any error code, such as P0562 (low battery voltage), is active.
- Use an advanced battery tester to check the voltage and resistance. The battery voltage should be around 12.4V or above, while the resistance should be as low as 2%.
- Test the alternator’s voltage using a multimeter. It should be around 12.4 to 12.6 volts with the engine off and 13.8 to 14.8 volts with the engine running.
- Look for loose battery cables or corroded terminals.
- Inspect the physical condition of parts like the brake pedal and vehicle speed sensors.
- Check the fluid level and condition of essential liquids like engine oil, coolant, and transmission fluid.
Your mechanic will perform certain repairs to resolve the issue based on the diagnosis.
Let’s look at some of them.
9 Essential Repairs to Get Your Start–Stop System to Work
To restore your car’s auto start-stop system, your mechanic will perform these common maintenance and repair procedures:
- Clean the corroded battery terminals
- Install a high-quality original battery and alternator
- Change the faulty sensors, their wires, and connectors
- Recalibrate the sensors
- Refill the coolant as per the recommended level
- Fix the radiator leak or replace it if it’s damaged
- Check for refrigerant leaks in the air conditioning system
- Update or reprogram your car’s computer
- Verify that there are no technical service bulletins or recalls by the manufacturer
After the required repairs, they’ll clear the error code and test-drive the car to see if the feature works.
Wondering whether repairing a start-stop system is worth the hassle?
Let’s weigh its advantages and disadvantages to make an informed decision.
What Are the Pros and Cons of an Auto Stop-Start System?
To understand whether this feature is a boon or bane, have a look at these points:
A. Advantages
- Reduces carbon emissions by up to 8%
- Increases fuel economy by up to 7.27% to 26.4%
- Offers quieter journeys
B. Disadvantages
- Causes premature wear of components like the starter motor, battery, and engine mounts
- Could lead to excess condensation in the exhaust system, causing corrosion of metal engine parts
- Has a high maintenance cost, as an original battery for this system is costly
- Is unhelpful in crowded junctions and turns where you can’t halt long enough for the system to engage
If you’re not convinced about its benefits and want to deactivate the start-stop system, keep scrolling to know whether that’s the best choice.
Should You Manually Disable the Start-Stop System?
You shouldn’t.
Auto start-stop systems reduce fuel consumption and exhaust gases. But if you disable it, you’re signing up for multiple visits to the gas station and putting the environment at risk.
However, if you’re driving to the hospital for an emergency or riding uphill, disabling the system is the right choice.
You can temporarily deactivate it using these two methods:
- Refer to the owner’s manual and access the vehicle settings to switch off the feature. Some vehicles also have a button to turn it off temporarily.
- Use an aftermarket auto start-stop eliminator.
CAUTION: There is no permanent way to turn off the system, so these methods may come with risks. For example, aftermarket eliminators purchased from unauthorized sellers can void your existing warranty. It’s best to do thorough research on products before making any changes to the system.
Access Smooth Auto Starts-Stops with AutoNation Mobile Service
Auto start-stop systems are revolutionary, as they help modern vehicles improve their fuel efficiency and prevent environmental damage. However, regular maintenance is necessary to support such a system.
If you suspect your start-stop function is failing, schedule an inspection ASAP.
Our expert mechanics at AutoNation Mobile Service can test your car battery and check the functionality of start-stop components, like the clutch pedal sensor, right from your driveway.
The best part?
We offer after-hours customer support and easy online bookings to make repairs accessible.
Contact us to get your auto start-stop system up and running.