13/01/2017
The sudden illumination of a warning light on your dashboard can send a chill down any driver's spine, especially when it pertains to something as critical as your vehicle's braking system. For owners of the Mercedes Vito or Viano 639 Mk2, understanding these signals is not just good practice, it's a matter of safety. One particular light, the brake warning indicator, demands immediate attention and comprehension. Ignoring it could lead to severe consequences, impacting not only your safety but that of other road users.
Understanding the Mercedes Vito/Viano 639 Mk2 Brake Warning Light
When the brake warning light illuminates on your Mercedes Vito or Viano 639 Mk2, the primary message it conveys is usually straightforward yet alarming: there is insufficient brake fluid in the brake fluid reservoir. This isn't a mere suggestion; it's a critical alert. Brake fluid is the lifeblood of your vehicle's hydraulic braking system. It transmits the force from your foot on the pedal to the brake calipers, which then press the brake pads against the discs, bringing your vehicle to a halt. A low fluid level means that the system's ability to generate and maintain the necessary pressure is compromised.
The implications of low brake fluid are severe. The most significant is that the braking effect may be impaired. This means your van might not slow down or stop as quickly or effectively as it should. Imagine a situation where you need to perform an emergency stop, and your brakes simply aren't up to the task – the consequences could be catastrophic. Therefore, the accompanying warning is stark: there is a risk of an accident. This isn't hyperbole; it's a direct warning that your vehicle is not safe to drive.
Immediate Action: What to Do When the Light Illuminates
Given the grave implications, your immediate action upon seeing this light is crucial. You must:
- Pull over and stop the vehicle safely as soon as possible: Pay close attention to road and traffic conditions. Look for a safe place away from moving traffic, such as a lay-by, a car park, or a quiet side street. Avoid sudden braking or swerving, as your braking performance may already be compromised.
- Secure the vehicle against rolling away: Once stopped, engage the parking brake firmly. If you're on an incline, place the transmission in 'Park' (for automatic) or a low gear (for manual) and, if possible, turn the wheels towards the kerb.
- Do not continue driving under any circumstances: This is a non-negotiable instruction. Even if the light flickers or seems to go off, the underlying issue remains. Driving with impaired brakes is an unacceptable risk.
- Do not add brake fluid: This point is often misunderstood. While it might seem logical to simply top up the fluid, doing so will not remedy the malfunction. Low brake fluid typically indicates either a leak in the system or severely worn brake pads, which cause the fluid level to drop as the calipers extend further. Topping up the fluid might temporarily extinguish the warning light, but it masks the real problem, potentially leading to a more severe failure down the line. It's akin to refilling a leaky bucket without patching the hole.
- Consult a qualified specialist workshop: This is the only safe and effective course of action. A professional mechanic will be able to diagnose the root cause of the low fluid level, whether it's a leak in the brake lines, calipers, master cylinder, or simply excessively worn brake pads. They have the expertise, tools, and genuine parts to carry out the necessary repairs safely and effectively.
- Observe the additional display messages in the multifunction display: Your Vito/Viano's multifunction display may provide further diagnostic information or specific instructions related to the brake system fault. Always check these messages for additional context.
Beyond Low Fluid: Common Causes of Brake System Warnings
While low brake fluid is the primary trigger for the specific warning light discussed, other issues can cause brake-related warning lights or symptoms. These often include:
- Worn Brake Pads: Modern vehicles, including the Vito/Viano, are equipped with pad wear sensors. These small electrical sensors are embedded in the brake pads and trigger a warning light (often a different one, or an additional message) when the pads have worn down to a critical level. This is a common and expected wear item.
- Brake Fluid Leaks: A drop in fluid level that isn't due to normal pad wear points to a leak. This could be anywhere in the hydraulic system: brake lines, hoses, calipers, master cylinder, or wheel cylinders (if applicable). Leaks are serious and require immediate professional attention.
- Faulty Sensors or Wiring: Sometimes, the issue isn't with the brakes themselves but with the sensors or their wiring. A damaged sensor or a broken wire can incorrectly trigger a warning light. This was a key part of the real-world scenario below.
- ABS/ESP System Faults: Separate warning lights typically indicate issues with the Anti-lock Braking System (ABS) or Electronic Stability Program (ESP). While distinct from the low brake fluid warning, these systems are integral to overall braking safety and require diagnosis if their lights illuminate.
A Real-World Scenario: Troubleshooting a Mercedes Vito W639 (User's Story)
To illustrate the complexities and satisfactions of vehicle maintenance, let's delve into a practical example from a fellow Vito owner. This experience highlights how seemingly disparate issues can arise and be resolved through diligent troubleshooting and a bit of mechanical know-how.
The owner of a Vito W639 56 plate faced a series of challenges, starting with conflicting information regarding the pad wear sensors. Some sources suggested one sensor per wheel, while others indicated only one on the front and one on the rear. This common confusion underlines the importance of accurate information when diagnosing vehicle faults.
A new, more pressing fault emerged before Christmas: the van wouldn't crank. This is a classic symptom often attributed to a flat or failing battery. The owner wisely invested in a new, uprated battery from Europarts. After fitting the larger battery, the van started, and the owner successfully completed some work. However, the problem resurfaced later that day at Sainsbury's – the van wouldn't crank again, despite the battery showing a healthy 14V standing voltage. This suggested the battery itself wasn't the issue, and theoretically, the alternator, which charges the battery, was also fine.
The mystery deepened when, after a few hours, the van inexplicably started. This intermittent nature can be particularly frustrating for diagnosis. However, the owner, a construction mechanical manager by trade, wasn't deterred. The next morning, using a homemade ramp, they bravely ventured under the van to locate and remove the starter motor. Swapping it out for a new one proved to be the solution. The van "went like a rocket!" – a clear indication that the starter motor was indeed the culprit behind the no-crank issue. This demonstrates that even when a battery seems fine, other components in the starting circuit, such as the starter motor itself, can fail.
Beyond the starting woes, the owner also tackled a persistent bulb warning light that illuminated when the brake pedal was pressed. This light, often indicative of a faulty brake light bulb, was also successfully resolved. While the exact cause wasn't detailed, it's common for electrical issues in one part of the vehicle to trigger seemingly unrelated warnings or to be resolved alongside other brake system repairs.
Finally, the original concern about the brake warning light, specifically related to the pad wear sensors, was addressed. The owner discovered that the offside front sensor had broken off, with the body of the sensor still on the pad but the wiring loom missing. This is a common failure point for these sensors, as they are exposed to harsh road conditions and can become brittle with age. Replacing the broken sensor and reconnecting the wiring loom immediately resolved the brake warning light issue. The owner's jubilant "Whoop whooop!!! SORTED!!!!" perfectly encapsulates the immense satisfaction of diagnosing and successfully repairing complex vehicle faults, especially for someone with a mechanical background.
This real-world example underscores several key takeaways: the importance of methodical troubleshooting, the potential for multiple seemingly unrelated faults to occur simultaneously, and the value of hands-on experience in resolving complex mechanical and electrical issues. It also highlights that while professional help is often necessary, some issues can be tackled by a competent DIY mechanic.
The Importance of Preventative Brake Maintenance
To avoid the unsettling experience of a brake warning light, preventative maintenance is paramount. Regular checks and servicing can identify potential issues before they escalate into serious problems. Here’s what you should consider:
- Regular Brake Fluid Checks: While you shouldn't top up low fluid without professional diagnosis, regularly checking the fluid level (when the engine is cold and the vehicle is on level ground) can give you an early indication of a potential problem. Consult your owner's manual for the correct procedure and fluid type.
- Brake Pad and Disc Inspection: During routine servicing, have your mechanic inspect the thickness of your brake pads and the condition of your brake discs. Worn pads are a common reason for fluid levels to drop, and replacing them before they're critically thin prevents the warning light from activating and ensures optimal braking performance.
- Hose and Line Inspection: Brake hoses and lines can degrade over time, leading to leaks. A thorough inspection for cracks, bulges, or corrosion can prevent a catastrophic loss of brake fluid.
- Professional Servicing: Adhere to your Mercedes-Benz service schedule. Regular professional servicing ensures that all components of your braking system are inspected, maintained, and replaced as needed. Brake fluid itself should be changed periodically (typically every two years, but check your vehicle's specific recommendations), as it can absorb moisture over time, reducing its effectiveness and leading to corrosion within the system.
Frequently Asked Questions (FAQs)
Can I drive with the brake warning light on?
Absolutely not. As stated, if the brake warning light (indicating low fluid or a general brake fault) illuminates, you must stop the vehicle safely as soon as possible and not continue driving. Driving with impaired brakes puts you and others at extreme risk.
Why shouldn't I just top up the brake fluid?
Topping up brake fluid without addressing the underlying cause only masks the problem. Low fluid is usually a symptom of either worn brake pads (in which case the fluid level will return to normal when new pads are fitted) or, more seriously, a leak in the hydraulic system. Adding fluid will temporarily extinguish the light but won't fix a leak, which could lead to sudden and complete brake failure.
How often should brake fluid be changed in my Vito/Viano?
Mercedes-Benz generally recommends changing brake fluid every two years, regardless of mileage. Brake fluid is hygroscopic, meaning it absorbs moisture from the air over time. This moisture can lower the fluid's boiling point, leading to 'brake fade' under heavy use, and can also cause internal corrosion within the brake system components.
What's the difference between the brake warning light and the ABS light?
The brake warning light typically indicates an issue with the fundamental hydraulic braking system, such as low brake fluid or a handbrake engagement. The ABS (Anti-lock Braking System) warning light, usually a distinct symbol, indicates a fault within the ABS system itself. While both relate to braking, an ABS fault might mean your anti-lock function isn't working, but your conventional brakes should still operate, albeit without the ABS safety net. A general brake warning light, however, signifies a more critical issue with the basic braking function.
How do brake pad wear sensors work?
Brake pad wear sensors are small, typically plastic-bodied sensors embedded into the brake pads. They contain a thin wire loop. As the brake pad wears down, the sensor makes contact with the brake disc, and the wire loop eventually breaks. This open circuit triggers a warning light on your dashboard, indicating that the brake pads need replacing. They are designed to alert you before the pads wear completely through, preventing damage to the brake discs and ensuring continuous braking performance.
Conclusion
The brake warning light on your Mercedes Vito or Viano 639 Mk2 is not a suggestion; it's a command. It demands your immediate attention and the correct response. Understanding its meaning – primarily low brake fluid – and knowing the crucial steps to take, including stopping safely and consulting a qualified specialist workshop, are vital for your safety. While some issues can be resolved with mechanical acumen, the complexities of modern brake systems often necessitate professional diagnosis and repair. Prioritise your safety and always heed the warnings your vehicle provides.
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