A pre-collision system malfunction message means your car’s automatic emergency braking can’t do its job right now. On a Toyota, the Pre-Collision System (PCS) relies on a radar sensor behind a cover at the front of the car and a front camera that looks through the windshield. If either one is blocked, too hot or cold, damaged or out of alignment, the system shuts itself off and warns you.
Often the cause is temporary, such as snow, dirt or a fogged windshield, and the message clears once the sensors can see again. If it does not clear, the system needs to be checked by a dealer. This guide explains what the warnings mean, what causes them and what you can safely do yourself.
What does pre-collision system malfunction mean?
The pre-collision system watches the road ahead for vehicles and other obstacles. If it predicts a collision, it warns you and, if you do not react, it can help apply the brakes.
A malfunction or unavailable message means the system has switched itself off because it cannot trust its sensors. Your normal brakes and steering still work, but you no longer have automatic braking or a collision warning, and related features such as radar cruise control may also be limited.
Toyota’s owner’s manual for the 2025 Sienna’s driving support systems says that a warning message can mean “a system may be temporarily unavailable or there may be a malfunction in the system.” When normal operating conditions return, “the message will disappear and the system will become operational.” If it does not disappear, Toyota says to contact a dealer.
Pre-Collision System Unavailable on a Toyota
“Pre-Collision System Unavailable” is the message Toyota shows when the radar can’t currently do its job. For this message, Toyota’s manual tells you to check whether anything is stuck to the radar sensor and its cover and remove it.
The manual also lists situations in which the message should clear on its own once conditions change or the car has been driven for a while:
- The temperature around the radar sensor is outside its operating range, such as after parking in strong sun or in extreme cold.
- The front camera cannot detect objects ahead, such as when driving in the dark, snow or fog, or with bright lights shining into the camera.
- The radar judges that it cannot properly recognize the surroundings.
If the message stays on after the sensors are clean and conditions are normal, the problem is more likely a fault in the sensor, its wiring or its alignment.
Why does my pre-collision system malfunction?
These are the most common causes, based on Toyota’s precautions for the radar sensor and front camera.
Dirty or blocked radar sensor
The radar sensor sits behind a radar sensor cover at the front of the car. Mud, snow, ice, water droplets or bugs on that cover can block it. Toyota says to keep the radar sensor and its cover clean and to clean them with a soft cloth to avoid damage.
Toyota also says not to attach accessories or stickers, including clear ones, to the radar sensor, its cover or the area around it. A plate frame, grille guard, bull bar or aftermarket grille that covers the sensor can cause the same warning.
Dirty, fogged or tinted windshield
The front camera looks through the windshield. Dirt, an oily film, condensation, ice or a sticker in front of the camera can stop it from seeing. Toyota’s manual says not to apply window tint to the windshield and to use the defogger to clear fog or ice in front of the camera.
Worn wiper blades that leave water in front of the camera can also cause problems, and Toyota recommends replacing them.
Camera too hot or too cold
After parking in strong sun or in extreme cold, the camera can be outside its operating temperature. Toyota suggests using the air conditioning to bring the temperature around the camera back to normal. The message should clear once it does.
Impact damage or a sensor out of alignment
Even a minor front-end bump can knock the radar out of alignment. Toyota says to have the vehicle inspected by a dealer if the radar sensor, front grille or front bumper takes a strong impact.
Recent repairs that need recalibration
Toyota’s manual says the radar sensor must be recalibrated after the radar sensor or front grille is removed and refitted or replaced, and after the front bumper is replaced. The front camera must be recalibrated after a windshield replacement. If the warning started after body work or new glass, recalibration is the likely fix.
How do I spot a pre-collision system problem?
The main signs are a message on the multi-information display, such as “Pre-Collision System Unavailable” or a malfunction message, together with the PCS warning light on the dash. The exact wording and light depend on the model and year, so check your owner’s manual for what each one means on your car.
You may also notice that radar cruise control or lane-keeping features stop working at the same time, because they rely on the same sensors.
How to fix a pre-collision system malfunction
Start with the simple checks, then move on to the dealer if the warning stays:
- Park safely and clean the radar sensor cover at the front of the car with a soft cloth. Remove any snow, ice, mud, stickers or accessories that cover it.
- Clean the outside of the windshield in front of the camera, clear any fog or ice with the defogger, and replace worn wiper blades.
- If the car has been sitting in strong sun or extreme cold, run the air conditioning or heater and drive for a while.
- Check for front-end damage, a loose bumper or grille, or anything mounted in front of the sensor.
- If the message still does not clear, book the car in with a dealer. They can read the fault codes, inspect the sensors and recalibrate them if needed.
Do not try to adjust or take apart the radar sensor or camera yourself. Toyota’s manual specifically warns against disassembling, modifying or painting the sensors.
Our take
Most pre-collision system warnings come down to something blocking the radar or the camera. Clean both, give the car some time to warm up or cool down, and drive normally. If the warning keeps coming back or will not clear, have it checked soon, especially after any front-end damage or windshield replacement.
Why did my collision light come on?
The collision or PCS light can come on when the system detects a possible collision, when it is temporarily unavailable because the sensors are blocked or outside their temperature range, or when there is a fault. If it stays on with a malfunction message after the sensors are clean, have the system checked.
How do I reset the pre-collision system on a Toyota?
There is usually no manual reset. Toyota says the message disappears by itself once normal operating conditions are detected. Clean the sensors, restart the car and drive for a while. If the message still does not go away, a dealer needs to diagnose the system and may need to recalibrate the radar or camera.
Can I drive my car with the pre-collision system unavailable?
Yes, the car will still drive and brake normally. But you will not have automatic emergency braking or collision warnings, and features such as radar cruise control may not work. Drive with extra care and get the fault fixed soon.