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There are many Mazda Demio problems that many owners face. These problems range from gearbox issues to ABS failure. We’ll break down the 10 most common Mazda Demio problems, explain the symptoms, outline the causes, and offer practical fixes for each. The Mazda Demio, also known as the Mazda 2 in some markets, made its way to the Japanese market in the 1900s as a supermini. It was classy. It was sporty. It was fun to drive.  And by 2008, the Mazda Demio was crowned World Car of the Year. 

On the compact car market, the Demio competes with the Honda Fit, Nissan March, and the Suzuki Swift. Reliability-wise, the Demio ended in 12th place out of 28 vehicles after WhatCar’s reliability survey in 2022. Overall, the Demio is known for its reliability, fuel efficiency, and compact design. But like any vehicle, it’s not immune to mechanical issues. Over time, owners have reported Mazda Demio problems that can affect performance, safety, or even comfort. 

1. Squealing From the Engine

If you hear a high-pitched squealing noise coming from the engine bay, it’s likely a sign of cam belt wear. You can hear the sound when starting the car or accelerating. This is one of the most common problems, and is particularly common in older Mazda Demio models built between 1998 and 2001. Old models are affected because the timing belt becomes noisy as it starts to degrade. Drivers may also notice inconsistent engine performance or unusual vibrations over time. 

The main cause of the squealing is a worn or glazed cam belt. Over time, heat and tension cause the rubber belt to harden or crack. This can reduce grip and lead to slippage, which produces the distinct squeal. If left unresolved, a damaged cam belt can eventually snap. This can cause severe engine damage, especially in interference engines.

To fix it, inspect the cambelt under the hood. If it looks shiny, cracked, or frayed, it’s time for a replacement. You should change the cam belt every 60,000 miles or five years, whichever comes first. A qualified mechanic can replace the belt and check the tensioner and pulleys at the same time.

2. Automatic Gearbox Problems

Some Mazda Demio owners, especially those with older automatic models, have reported problems with the gearbox. Some experience rough shifting of the gearbox or failing to engage certain gears. You might notice jerky transitions when accelerating or decelerating, or delayed gear changes. If the problem is severe, the Demio might have a complete gearbox failure to shift into reverse or drive. These symptoms typically get worse with time and can affect drivability and safety. In my experience, the reverse gear usually dies first before the rest of the transmission system fails. 

The root cause of the gearbox issue in the Demio often lies in worn transmission components, degraded transmission fluid, or issues with the valve body. In some cases, electrical faults such as bad solenoids or a failing transmission control module (TCM) can interfere with proper shifting. Lack of regular transmission maintenance is also a common contributor to these problems. 

To fix the gearbox issue, start with a full transmission fluid check and flush if necessary. Dirty or low fluid can cause most shift-related problems. If that doesn’t help, have a qualified mechanic inspect the solenoids, valve body, and TCM. In some cases, a software update may resolve the shifting issues in newer models. If there is severe wear or internal damage, your Mazda Demio may require a gearbox rebuild or replacement.  

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3. Carbonised Engine

One of the most reported Mazda Demio problems is the carbonized engine issue. As your Demio racks up mileage, carbon deposits can begin to build up inside the engine. This is common, especially if it’s regularly run on low-quality fuel. This build-up can affect critical components like the injectors, intake valves, and pistons. You may notice symptoms such as rough or uneven idling, engine misfires, a drop in fuel efficiency, or a general lack of power during acceleration. 

The carbon buildup problem is particularly common in older or neglected vehicles. As carbon builds up, it restricts airflow and disrupts combustion. This leads to poor engine performance and long-term damage if left unresolved. It can also make the engine more prone to knocking and increased emissions. 

The most effective solution to Demio’s carbon buildup issue is to have an engine carbon clean performed. This service removes carbon deposits from the key components. For best results, consider pairing the carbon clean with a fuel injector service and using higher-quality fuel moving forward.

4. ABS Failure

ABS sensor failure is a known issue in older Mazda Demio models. When one of the sensors fails, it typically triggers the ABS warning light on the dashboard along with a corresponding fault code. Drivers may also notice symptoms such as the wheels locking under hard braking, reduced braking stability, or a pulsing sensation through the brake pedal during stops.

However, other issues can cause the ABS light to come on. These are issues like damaged wiring, a dirty sensor ring, or problems with the ABS control module. In most Demio cases, it is the wheel speed sensor that’s at fault due to age or corrosion. 

The fix to the ABS failure is simple: replace the faulty sensor. Driving without a working ABS can compromise braking safety, especially in wet or slippery conditions. 

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5. Air Conditioning Failure

Air conditioning issues are common in second and third-generation Mazda Demio models, especially those built between 2015 and 2019. Owners often report that the system fails to blow cold air, making driving uncomfortable during warmer months. In some cases, a weak airflow or strange noises are coming from the vents. And if that’s the case, you may be looking at a deeper system trouble. 

The AC failure in the Demio is caused by several issues, such as refrigerant leaks, a failed blower motor, or a malfunctioning AC compressor. A worn-out cabin filter or electrical faults in the control module can also be to blame. Over time, components in the AC system can wear out or develop leaks.

To fix the issue, book an air conditioning service to check for leaks, re-gas the system, or replace the blower motor or other faulty components. 

6. Diesel Injector Issues

Owners of 2007–2015 Mazda Demio models with the 1.4 or 1.6-litre diesel engines commonly report injector-related problems. These engines can be noisy. But when the injectors start failing, you may notice more serious symptoms like power loss, engine misfires, rough idling, or even stalling. In many cases, the check engine light will also come on. 

The root of the issue is usually faulty or worn-out diesel injectors that are no longer delivering fuel at the correct pressure or spray pattern. Remember when we talked about Carbon build-up? Well, the carbon build-up and contaminated fuel can cause the injectors to clog or leak. This can affect engine performance and fuel efficiency. 

The solution is to replace the faulty injectors. This can be costly depending on the number of injectors involved. A diagnostic check will confirm which ones are faulty. Replacing a single injector may cost between $150 and $300 (or more with labor).

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7. Blocked DPF (DPF Warning light)

Mazda Demio diesel models are at risk of developing a blocked Diesel Particulate Filter (DPF). This is common in models used mostly for short trips around town. The DPF captures and burns off soot from the exhaust. However, it needs high temperatures, usually reached during long motorway drives, to regenerate properly. Without this, the filter clogs up over time.

When the DPF is blocked, you may notice a sharp drop in power and poor fuel economy. You may also notice a strong diesel smell from the exhaust or the car going into limp mode. The engine light or DPF warning light may also appear on the dashboard. These symptoms mean the system is struggling to manage emissions and airflow. 

To fix the blocked DPF Mazda Demio problems, you have to replace the filter. But this is an expensive fix. A professional DPF clean will usually solve the issue if caught early. This involves flushing out the built-up soot using specialised equipment. 

8. The Engine Has Died

One of the less common Mazda Demio problems is engine failure. Some owners reported complete engine failure at relatively low mileage, often just after 98,000 miles. This issue can occur suddenly and without prior warning signs. It can leave the vehicle completely inoperable. In many cases, the engine seizes or suffers internal damage severe enough that it cannot be repaired. 

The root cause of this failure hasn’t been universally acknowledged by Mazda. However, reports point toward long-term internal wear, possible oil starvation, or a known weak point in the engine design. Unfortunately, it seems this problem is more of a design flaw than a maintenance issue. This means even well-kept engines can suffer from it unexpectedly. 

Once the engine fails, the only practical solution is to replace it entirely. I wouldn’t recommend rebuilding it. The best route is sourcing a second-hand engine in good condition. If you’re buying a used Demio from this generation, check the mileage. 

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9. Smoke From Dashboard

Some owners of the 1989-2002 Mazda Demio reported seeing smoke rising from the dashboard, usually near the ignition port. This issue can appear suddenly and is understandably concerning due to the potential fire hazard it poses. 

The problem comes from carbonised grease buildup inside the ignition switch. Over time, the grease between the electrical contact points becomes conductive. This leads to heat generation and smoke. This fault was serious enough to trigger a recall for affected Mazda Demio models during that manufacturing period. 

To fix this issue, disassemble the ignition switch and clean it thoroughly. After cleaning, apply a fresh non-conductive lubricant to prevent future buildup. If any part of the switch has suffered heat damage, replacement of the entire ignition unit is the safest solution.

10. Misfiring

If your Mazda Demio is suffering from engine misfires or feels sluggish during acceleration, one of the most likely causes is a faulty coil pack. This component delivers the spark that ignites the air-fuel mixture in the engine. When it begins to fail, you may notice uneven power delivery, rough idling, or hesitation when accelerating. 

Another possible cause of misfiring is the spark plug leads. These leads transfer the electrical current from the ignition coil to the spark plugs. If they degrade or crack over time, they can cause misfires, especially under load. 

To resolve the issue, start by testing the coil pack using a multimeter or swap it with a known good unit if available. If the coil pack is faulty, replacing it should fix the misfire. If the coil checks out fine, the next step is to replace the spark plug leads.