Five Reasons a Car Wiper Runs Continuously or Will Not Stop

A wiper that will not stop, or that runs when you have not asked it to, is a common and easily ignored fault. It wears the wiper rubber, drains the battery on a vehicle that stands for days, and on some models leaves the wiper in a position where it cannot be switched off, which is a genuine safety concern in heavy rain.

This guide covers the causes, and how to stop the wiper doing further damage in the meantime.

How a Wiper System Works

Rather more than a motor and two arms. The system includes the wiper motor, which contains a park switch operated by a cam inside the motor housing, the wiper linkage that distributes motion to both arms, the wiper blades, and on a modern vehicle the body control module that receives the switch input from the steering column and commands the motor, and which also controls the intermittent, the rain sensing, and the wash function.

That park switch is the key to most of the faults. When the wiper is switched off, the motor drives the linkage to the end of its travel, the cam operates the park switch, and the motor stops with the blades in the park position. If the park switch, the motor, or the control module does not complete that sequence, the wiper keeps running.

The Five Causes

1. A Worn Motor Brushes or a Failed Motor

The most common cause. Carbon brushes wear out, and a motor with brushes that have worn to their limit will stall and judder. The recognisable symptom is a wiper that moves slowly, stops partway, and then restarts, or one that runs at a varying speed. A motor can also fail in a way that leaves it energised, so it never stops because it never completes the park sequence. Replacing the motor is the usual repair and it is a moderate job because of the linkage and the cowl.

2. A Faulty Wiper Park Switch

The second most common, and it is inside the motor. The switch itself can fail, or the cam that operates it can crack or break, and in either case the motor never receives the instruction to stop. The symptom is a wiper that runs continuously with the blades moving normally, which is often accompanied by a clicking sound that repeats as the arms reach the end of travel. This requires the motor to be opened, and on many vehicles the switch is available separately.

3. A Faulty Switch or Control Module

The column switch on an older vehicle has contacts that wear and can fail to latch in the off position, so the motor continues to receive power. On a modern vehicle the body control module processes the input and the output, and both a failed switch input or a failed module output produce a wiper that will not stop. Testing at the motor is what distinguishes these: if the motor continues to receive power with the switch in the off position, the fault is upstream in the switch or the module.

4. A Binding Linkage or a Blocked Cowl

The linkage is mechanically simple, but it is exposed to the weather and to the water that runs off the windscreen. A hinge that has corroded, a pivot that has seized, or a cowl that is packed with leaf litter and dirt can prevent the motor from reaching the end of its travel, so the park switch is never operated. A wiper that moves slowly and heavily, or one that has a distinct gritty feel, points at this rather than at the motor.

Many vehicles have a wiper linkage that fails on the driver's side and leaves the passenger side intact, which is a pattern that makes a linkage fault rather than a motor fault much more likely. The cowl below the windscreen also needs to be kept clear so that water drains properly, and a blocked cowl is a common cause of water ingress into the cabin as well.

5. A Malformed or Incorrect Blade

Less commonly the cause of a wiper that will not stop, but a real cause of a wiper that jams. A blade that is the wrong length, that is fitted backwards, or that has a lifting mechanism that has locked will bind at a particular point on the travel. A wiper that stops at a consistent position rather than moving erratically suggests a mechanical bind rather than an electrical fault. A blade that is heavily worn can also chatter and judder, which loads the motor and eventually damages the drive.

Making the Wiper Stop Safely

If the wiper is running continuously, the priority is stopping it without damaging the linkage or the motor. The reliable method is to disconnect the battery, which removes power to the motor regardless of the switch state. The wiper arms will remain where they are, and it is worth noting that on many models the arms are spring-loaded against the windscreen, so they can be lifted carefully once the battery is disconnected.

Do not try to stop it by forcing the arms, because the linkage can be bent and the motor strained, which turns a simple repair into a much larger one. Do not jam the wiper blade in a position to stop it, because that loads the motor and can burn out the park switch or the motor itself.

Once the vehicle is running again, be aware that many models require the wiper to be cycled through two full cycles and then left in the off position for a period before the module recalibrates its position reference. Skipping that step results in a wiper that sits a few centimetres above the usual park position.

Repairing It Properly

Establish whether the fault is electrical or mechanical before ordering anything, because the two lead to entirely different parts. Disconnecting the motor and testing it directly on a battery distinguishes a motor fault from a control fault, and if the motor runs and parks correctly on direct power, the problem is in the switch, the module, or the wiring. Checking whether the blades move smoothly by hand, with the motor disconnected, distinguishes a mechanical bind.

The related subject of wiper blade care, which is where most of the cost saving actually comes from, is covered in our guide to wiper maintenance, and a wiper that has been replaced recently along with this repair is the sensible combination. For the electrical side of the same system, our guides to common electrical faults explain how to test the supply and the earth.

If this guide was helpful, you may also want to read dashboard warning lights explained to see whether a battery warning has also appeared, since a wiper left running will flatten a battery overnight. It also fits within a general vehicle care routine, where checking the wipers is one of the highest-value checks for the money.