Why isn’t the windshield wiper speed changing?

Sometimes you're driving in pouring rain, and your wiper blades seem to have a mind of their own—stuck on one speed, no matter what you do. It’s frustrating, distracting, and can quickly become a serious safety risk.

When your windshield wiper speed isn’t responding, it usually signals an issue with the relay, control module, or intermittent circuit. Fixing these can restore full control and visibility.

This isn’t just a minor annoyance. For fleet managers and vehicle distributors, it can lead to driver complaints, safety issues, and maintenance headaches. Let’s take a closer look at what’s going wrong—and how we, at Runex Auto, have helped solve these exact problems with reliable wiper solutions.

Why are my windshield wipers slow speed not working?

You’re cruising down the motorway, and the rain starts falling lightly. You switch to the low-speed setting—but nothing happens. The wipers only respond on high. Why?

When the slow speed on your windshield wipers isn’t working, the likely culprits are a damaged relay, corroded wiring, or a failing wiper motor. At Runex Auto, our upgraded relay kits are built to handle continuous load, reducing failure rates dramatically.

Breaking it down: What really causes low-speed failures?

When our team at Runex Auto¹ evaluated slow-speed wiper issues in commercial fleets, we found three recurring causes:

1. Burned Out Relays

A basic relay failure can knock out specific speed settings. We saw this first-hand in a UK-based fleet running vans across Manchester. Drivers were stuck on full-speed wiping during light drizzle—not ideal. Swapping to our upgraded relays fixed the issue instantly.

2. Corroded Connectors or Grounds

Low voltage delivery through worn wiring can make the wiper motor act as if it’s defective. In reality, the fault lies in the connector harness. We recommend distributors stock our corrosion-resistant harness kits to avoid this.

3. Worn Wiper Motors

Though less common, over time wiper² motors lose torque—particularly on low-speed operations. We advise replacing them before they fail completely. Our OEM-grade motors are tested for over 500,000 cycles.

Problem	Cause	Runex Solution
Slow speed not working	Faulty relay or corroded wiring	High-capacity relay and harness kit
Wipers only work on high speed	Dead low-speed circuit in motor	Long-life dual-speed motor
Intermittent wiping skipped	Faulty timing controller or relay	Modular controller upgrade

Why is my windshield wiper going at different speeds?

Sometimes your wipers start slow, then go crazy fast. Or worse—jerky, inconsistent wiping. That’s not normal.

Inconsistent wiper speeds are typically caused by malfunctioning wiper relays, worn-out control modules, or internal motor feedback failures. These are exactly the weak points our Runex wiper systems are designed to reinforce.

What leads to inconsistent speeds?

Fleet operators we work with frequently report wiper speed irregularities, especially on older vehicles. Here’s what we’ve found in the field:

1. Voltage Instability

Old wiring and tired relays can’t regulate current properly. When voltage dips, wipers slow down—or glitch. Our Runex power³-stabilized relay systems help maintain a clean signal.

2. Control Module Issues

The speed of modern wipers is regulated electronically. If the timing logic fails, speed control gets erratic. We provide plug-and-play replacements for fleet managers needing a fast fix.

3. Physical Drag

Worn blades or bent wiper arms add resistance. That feedback can confuse older motors. All Runex blades are tension-balanced to maintain consistent wipe pressure across the windshield⁴.

Symptom	Potential Cause	Runex Fix
Jerky motion	Unstable relay or voltage	High-tolerance relays
Sudden speed changes	Logic board error in controller	Certified replacement modules
Speed delay after switching	Weak feedback signal in system	Signal-calibrated motor units

What controls the windshield wiper speed?

Wiper speed seems simple—low, high, and maybe intermittent. But behind the scenes, a lot is happening.

Windshield wiper speed is controlled by a combination of the driver switch, wiper relay, control module, and the motor’s internal settings. Runex Auto optimizes each link in this chain for consistent, weather-resistant performance.

What’s inside the wiper speed system?

Let’s walk through the four key parts:

1. Driver Input Switch

This is what your hand touches—but it's just the beginning. If the switch sends the wrong signal, the system won’t respond. All our Runex-approved switches are tested for accurate multi-speed toggling.

2. Wiper Relay

This is the “gatekeeper” that directs power where it needs to go. A faulty relay equals unpredictable performance. Our relays use copper contacts and thermal-resistant shells for long-term use.

3. Control Module

Think of this as the brain. It interprets signals and manages speed changes and intermittent timing. Many failures happen here, especially when exposed to moisture. Runex modules come sealed and pre-tested.

4. Wiper Motor

The muscle behind the motion. Some motors have built-in logic, others rely on external control. Our motors are dual-mode with internal override, so you’re covered no matter what system your vehicle uses.

Component	Role in Speed Control	Runex Features
Driver Switch	Sends input	Multi-speed with snap-toggle design
Wiper Relay5	Transfers power	High-capacity, copper-core relays
Control Module6	Interprets speed logic	Moisture-proof, plug-in ready
Wiper Motor	Executes motion	Internal override, load-resistant housing

Why is the intermittent wiper setting not working?

You set your wipers to intermittent mode expecting convenience—but they don’t pause like they should. Or they just don’t start at all.

When the intermittent wiper setting fails, it’s often a failed timer circuit or a degraded relay. Runex Auto builds timing modules specifically to handle variable UK rain conditions—light drizzle to heavy downpour.

Why do intermittent settings stop working?

One client we supported had a fleet of 30 vehicles all showing the same issue—intermittent wipers refused to function. We replaced every timing relay with our upgraded modules⁷. Result? 100% uptime in 60 days of testing.

1. Timer Relay Failure

Over time, timers lose accuracy or just fail to activate. Cheap relays degrade quickly. We build ours with automotive-grade resistors and weatherproof shells.

2. Switch Contact Wear

Sometimes, the stalk/switch can’t connect properly anymore. A simple click fails to send the right signal. Our switch sets include reinforced contact pads to reduce this.

3. Software Conflict

In newer vehicles, wipers can sync with rain sensors or vehicle ECUs. Software conflicts can block intermittent modes. Our modules are OEM-compatible to prevent these glitches.

Issue	Reason	Runex Upgrade8
No intermittent mode	Dead timer relay	High-resistor sealed relays
Delayed intermittent activation	Switch wear	Reinforced toggle-switch set
Skipped intermittent cycles	Software mismatch	ECU-compatible smart module

Conclusion

Windshield wiper⁹ speed problems might seem minor—until you’re caught in a storm with no visibility. From faulty relays to glitchy control modules, the chain of control must be reliable. At Runex Auto, we’ve built our wiper solutions to handle the harshest weather and the heaviest use, especially for fleets and distributors across Europe. Whether it’s low-speed failure, inconsistent wiping, or intermittent mode not responding, we’ve engineered answers that restore safety and trust.