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lou's garage

Every single customer that walks through my door as of late is complaining or questioning their vehicle’s fuel economy. And no wonder, as the current gas pricing absurdity has drivers to taking a critical look at their fuel expenditures.

Anyone with an Internet connection can easily research the most basic practices to squeeze a few extra kilometres out of a litre of fuel. Mileage-based articles dealing with tire pressures and tune ups are aplenty, but I would like to give you something you may not be aware of that can still hit you hard at the fuel pump.

Most people have heard the term oxygen sensor, but don’t really understand its role in the engine-management system. Older cars from the 1990s featured the rudimentary first-generation sensor, but they have since evolved into more robust units called wide-band oxygen sensors and air-fuel ratio sensors. These sensors have the simplest of jobs: they measure the amount of oxygen in the exhaust. I will refer to them all as oxygen sensors.

Consider for a moment that most of your engine’s sensors are pre-combustion, that is, they are analyzing conditions before the fuel is injected into the engine. The oxygen sensor however, is the lonesome sensor after-the-fact that monitors how efficiently your engine is running and burning its fuel. By measuring the remaining oxygen content in the exhaust, the oxygen sensor can send relevant information which allows the Powertrain Control Module (PCM) to calculate rich or lean condition. If the oxygen content is low, the PCM determines that a rich condition is occurring and subtracts fuel overall, and vice versa.

The oxygen sensor by design is constantly flipping or cycling from rich to lean as throttle and driving conditions are also ever changing. As these oxygen sensors age, the cycling process slows significantly, resulting in information that cannot be acted on quickly. The PCM’s response time also diminishes accordingly as this key sensor ages.

The result is a slow, but steady decline in fuel economy that can take years to notice. You can expect a reduction in fuel economy to be about 5 per cent at the first signs of age, all the way up to an extreme case of 40 per cent when it has reached the end of its life.

The average effective lifespan of one of these contemporary sensors is approximately 160,000 kilometres. That does not mean that the sensor has completely failed and is useless at this mileage. It just means that if you are trying to figure out how those extra miles have disappeared since the car was brand new, you might want to look here once you have extinguished all other obvious maintenance and repair paths.

Four-cylinder engines will have two sensors, while six- and eight-cylinder engines will have three or four oxygen sensors. Only the primary oxygen sensors, which are also known as upstream, are used for fuel management. They are located before the catalytic convertor, hence the label upstream. The post convertor oxygen sensors are only used to monitor the health status of the catalytic convertor and have nothing to do with fuel economy.

Should you replace this sensor? When the PCM detects a sensor that has totally failed, it will turn on your Malfunction Indicator Lamp (MIL). But there can be quite a period between a sensor that has failed and one that is merely slow to respond. Your service provider can use an advanced scan tool to scrutinize the sensors’ waveform output looking for a slow-to-respond sensor.


Your automotive questions answered

Hi Lou, I found your column interesting today as I’ve wished for a GTI wagon. How would the “tuning” you write of compare to what VW does. VAG seems to have a string of that engine with horsepower all the way from 170 to more than 300. Your 242 horsepower is, I think, roughly, what “clubsport” version offered in Europe offers. The idea of a VW wagon, tuned to GTI horsepower is attractive. My Volvo V70 is getting on in the years and my BMW E30 touring is getting to be too classic to be a daily driver. Thanks, Sam W.

As I headed into work one recent morning, I was leisurely passed on the highway by a new Audi RS6 wagon. As I gazed longingly at it, I felt momentarily and temporarily inadequate in my little VW SportWagen. I then fondly remembered my 2001 Audi S4 wagon that I owned for many years. I absolutely loved the way that car drove and put power to the ground. Fortunately, reality set back in, and I also then remembered the amount of fuel it consumed and the generous time it sat on one of my hoists, broken, waiting for parts or the time to actually fix it.

Europeans love their sport wagons, but here in North America, Crossovers, SUV’s and pickup trucks reign supreme. A SportWagen with a GTI or R drivetrain would probably make its way into my driveway, but I just don’t see that happening because the North American market is just not there.

VW GTIs and R models are more than just a software tune, they include massaged engine, induction, suspension and brake components as part of that complete sport package. Tuning my own SportWagen has crossed my mind several times as it is now out of its major component factory warranty period. For me though, I’m at the age that while I still want a wagon, I am now too frugal to pay for the extra fuel and subsequent repairs.

A solitary tune is a poor attempt at a sporty wagon without all the extras mentioned above. I like my work-to-home commuter vehicle to be quiet and comfortable with zero fuss, and luckily for me, I have other toys that fill the fun check box.


Hi, I read that one of your readers asked about the rust repair warranty from Audi.

Although your answer related to the fact that the car was a U.S. car, Audi’s repair of Canadian purchased cars is not much better. We have had rust issues on two 2010 Audis. Although the warranty is for 12 years, Audi only paid 50 per cent of the cost, and the repair had to take place at a shop designated by Audi. This of course begs the question as to how much Audi actually contributed, which is unknown. In the end, it might be better to find a reputable repair shop and pay for the repair yourself. Nothing in the warranty suggests that part of the cost is to be borne by the owner.

Thanks, Paul L.

The fine print for corrosion warranties offered by all new car manufacturers offers exclusions and omissions that can be exhausting for the average owner to decipher. Most however afford a full manufacturer warranty paid claim only when the metal is completely perforated. Bubbles, paint blemishes are rarely paid for in full past the five-year mark. Even within the first five years, there are omissions related to rust repairs because of stone chips. I applaud the fact that you managed to get even 50 per cent coverage on the age of your cars. Approved repair facilities are a whole other subject, which I too have my theories about, but lack the inside knowledge to offer a qualified opinion.

Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail globedrive@globeandmail.com, placing “Lou’s Garage” in the subject line.

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