Ten years ago, buying a used car was all about checking the oil, kicking the tyres, and making sure the air conditioning ran cold. If the engine sounded healthy and the gearbox shifted smoothly, you were usually in the clear.
Today, that checklist is dangerously incomplete.
Modern vehicles are rolling networks of computers, cameras, and radars. Advanced Driver Assistance Systems (ADAS)—features like Automatic Emergency Braking (AEB), Lane Keep Assist, and Adaptive Cruise Control—are now standard on millions of used cars hitting the market. While these systems save lives, they can also destroy your wallet if you buy a car with hidden defects.
A misaligned radar or a camera that won’t calibrate isn’t a cheap fix; it can easily cost over $1,000 to rectify. Worse, you might not know anything is wrong until the system fails to react in an emergency.
Before you hand over your hard-earned cash, use this guide to audit the ADAS features on your next used car.
1. The Windscreen Walkaround
The most critical sensor on most modern cars is the Front Facing Camera. It sits behind the rearview mirror, pressed against the glass. It controls your Lane Keep Assist, reads speed signs, and often helps with emergency braking.
Because it looks through the windscreen, the condition of the glass is paramount.
What to Look For:
- Non-OEM Glass: Check the brand logo (the “bug”) in the bottom corner of the windscreen. Does it match the car brand (e.g., Toyota, Honda, Ford)? If it says “Fuyao” or “XYG” while the rest of the windows say “Toyota,” the windscreen has been replaced. This isn’t automatically bad, but it requires proof that the camera was recalibrated when the glass was changed.
- Chips and Cracks: Look closely at the area directly in front of the camera lens. Even a tiny stone chip or a smear of old wiper fluid in this “sensor zone” can confuse the camera, causing the system to shut down unexpectedly.
- Loose Brackets: From the outside, look at the plastic housing holding the camera. does it look flush against the glass? If it’s peeling away or looks loose, the camera cannot see straight.
The Deal Breaker: If the windscreen is cracked and the seller says, “Don’t worry, it’s just cosmetic,” walk away or demand a discount equal to the cost of a replacement plus a calibration.
2. The Bumper & Radar Audit
Many cars use a radar sensor for Adaptive Cruise Control (ACC) and Front Collision Warning. This is usually located in the front grille (often behind a flat plastic square) or mounted low in the bumper.
Because they sit low on the front of the car, radars are prime targets for parking bumps and stone strikes.
What to Look For:
- Impact Damage: Look for scuffs, cracks, or dents near the sensor. A radar sensor relies on precise angles—literally down to the millimetre. If the bumper is pushed in even slightly, the radar might be pointing at the ground or the sky.
- Paint Overload: If the car has had a respray, check if the sensor area was painted over. Radars can transmit through plastic, but heavy layers of paint or body filler (Bondo) can block the signal. If the paint looks thick or uneven on the sensor cover, be suspicious.
- Aftermarket Grilles: Does the car have a custom “sports” grille? If the previous owner swapped the grille, they might have relocated or removed the radar bracket.
3. The Dashboard “Menu Dive”
Don’t just start the engine and drive off. You need to check what the computer is telling you before you move.
The Startup Cycle
When you first turn the ignition on (before starting the engine), watch the dashboard. You should see all the warning lights illuminate—ABS, Airbag, and ADAS icons (like a car with circles around it or lane lines).
- What you want: The lights turn on (bulb check) and then turn off.
- The Red Flag: If the ADAS lights never turn on, the previous owner might have taped over the LED or disabled the system to hide a fault.
The Settings Check
Go into the vehicle settings menu on the infotainment screen. Look for “Driver Assist” or “Safety Settings.”
- Are the boxes checked?
- Try to toggle them off and on.
- If a feature is greyed out or says “System Unavailable,” that is a hard fault. It means the sensor is broken, unplugged, or misaligned.
4. The Test Drive: Trust but Verify
You cannot test Automatic Emergency Braking (AEB) safely on a test drive—please do not try to drive at a wall! However, you can test the convenience features that rely on the same sensors.
Test 1: Adaptive Cruise Control (ACC)
On a clear road, set the cruise control and follow a car at a safe distance.
- Pass: Your car detects the vehicle ahead (usually showing an icon on the dash) and slows down automatically when they slow down.
- Fail: The car rushes up to the vehicle ahead without slowing, or the system beeps and disengages immediately.
Test 2: Lane Keep Assist (LKA)
Find a road with clear white lines.
- Pass: The dashboard icon turns green (or solid) when it sees the lines. If you drift near the edge, it gives a gentle nudge or warning beep.
- Fail: The system never “locks on” to the lines, even on a clear day. This often indicates a dirty camera or a bad calibration.
Test 3: Blind Spot Monitoring
This is the easiest to test.
- Pass: The light in the side mirror illuminates whenever a car passes you.
- Fail: The light stays on permanently (wiring fault) or never turns on at all.
5. The “Hidden” History
Finally, ask the seller for the service history, but look for specific keywords. You aren’t just looking for “Oil Change.”
Look for terms like:
- “ADAS Calibration”
- “Sensor Alignment”
- “DTC Clearing”
- “Windscreen fitted”
If you see a receipt for a body repair or a windscreen replacement, you must see a corresponding receipt for calibration. If the car was smashed and repaired but never calibrated, you are buying an unfinished project. The safety systems might be active, but they could be looking in the wrong direction.
Summary: Leverage is Key
Finding an ADAS issue doesn’t mean you shouldn’t buy the car. In fact, it can be a powerful negotiating tool.
If you spot a misaligned radar or a windscreen chip in the camera zone, you know that’s a massive repair bill. Point it out. Use it to lower the price. But never, ever assume it will be a “cheap fix.” In the world of ADAS, cheap fixes are a thing of the past.
Buying smart means knowing what you’re looking at. Stay safe, and check those sensors.
Hiran Alwis is an automotive lecturer and ADAS specialist with over 15 years of experience in diagnostics, advanced safety systems, and technical training. He founded ADAS Project to help everyday drivers and workshop technicians understand and safely use advanced driver assistance systems.