Every customer that walks through my door lately complains or questions the fuel economy of their vehicle. And it’s no wonder, because the current absurdity of gas prices makes drivers take a critical look at their fuel expenses.
Anyone with an internet connection can easily research the most basic practices for extracting a few extra miles from a liter of fuel. Mileage-based articles dealing with tire pressure and tune-ups are plentiful, but I’d 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 have since evolved into more robust units called wideband oxygen sensors and air-fuel ratio sensors. These sensors have the simplest job: they measure the amount of oxygen in the exhaust gases. I will call them all oxygen sensors.
Consider for a moment that most of your engine’s sensors are pre-combustion, meaning they scan for conditions before fuel is injected into the engine. However, the oxygen sensor is the only afterthought sensor that monitors the efficiency of your engine and its fuel combustion. By measuring the oxygen content remaining in the exhaust gases, the oxygen sensor can send relevant information that allows the powertrain control module (PCM) to calculate the rich or lean condition. If the oxygen content is low, the PCM determines that a rich condition is occurring and subtracts the overall fuel, and vice versa.
By design, the oxygen sensor constantly switches or cycles from rich to lean, as acceleration and driving conditions also constantly change. As these oxygen sensors age, the cycling process slows dramatically, resulting in information that cannot be acted on quickly. PCM response time also decreases accordingly as this key sensor ages.
The result is a slow but steady decline in fuel economy that can take years to be noticed. You can expect a reduction in fuel economy of around 5% at the first signs of age, up to an extreme case of 40% when it has reached the end of its life.
The average effective life of one of these contemporary sensors is around 160,000 kilometres. This does not mean that the sensor is completely faulty and useless at this mileage. It just means that if you’re trying to figure out how those extra miles have gone since the car was new, you might want to look here once you’ve turned off 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 primary oxygen sensors, also called upstream, are used for fuel management. They are located before the catalytic converter, hence the upstream label. Post-converter oxygen sensors are only used to monitor the health of the catalytic converter and have nothing to do with fuel economy.
Should this sensor be replaced? When the PCM detects a totally faulty sensor, it will illuminate your malfunction indicator lamp (MIL). But there can be a long period between a sensor that is failing and one that is simply slow to respond. Your service provider can use an advanced analysis tool to examine the waveform output from the sensors for a slow-responding sensor.
Answers to your automotive questions
Hi Lou, I found your column interesting today because I wanted a GTI station wagon. How does the “tuning” you write compare to what VW does. VAG seems to have a string of this engine with horsepower ranging from 170 to over 300. Your 242 horsepower is, I think, about what the “clubsport” version offered in Europe offers. The idea of a VW wagon, tuned to GTI power is appealing. My Volvo V70 is getting old and my BMW E30 Touring is becoming too classic for everyday driving. Thank you, Sam W.
On my way to work one recent morning, I was quietly passed on the freeway 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 station wagon which I owned for many years. I absolutely loved the way this car drove and put the power to the ground. Luckily reality came back, and I also remembered how much fuel it used and the generous amount of time it spent on one of my hoists, broken, waiting for parts or time to fix it .
Europeans love their sport wagons, but here in North America, crossovers, SUVs and pickups reign supreme. A SportWagen with a GTI or R drivetrain would probably make its way up my driveway, but I just don’t see that happening because the North American market just isn’t there.
The VW GTI and R models are more than just software tuning, they include engine, induction, suspension and brake components massaged as part of this comprehensive sports 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 where even though I still want a wagon, I’m now too frugal to pay for the extra fuel and subsequent repairs.
A solitary air is a bad attempt at a sports wagon without all the extras mentioned above. I like my work-from-home vehicle to be quiet and comfortable, hassle-free, and luckily for me, I have other toys that tick the fun box.
Hello, I read that one of your readers asked about Audi’s rust repair warranty.
Although your answer is that the car was an American car, Audi’s repair of cars purchased in Canada isn’t much better. We had rust issues on two 2010 Audis. Although the warranty was 12 years, Audi only paid 50% of the cost and the repair had to be done at an Audi-designated shop. This of course raises the question of how much Audi actually contributed, which is unknown. In the end, it might be best to find a reputable repair shop and pay for the repair yourself. Nothing in the warranty suggests that any part of the cost is the owner’s responsibility.
Thank Paul L
The fine print of corrosion warranties offered by all new car manufacturers offers exclusions and omissions that can be overwhelming for the average owner to decipher. However, most offer a full manufacturer’s warranty only when the metal is fully perforated. Bubbles, paint imperfections are rarely paid for in full beyond the five year mark. Even in the first five years there are omissions related to rust repairs due to stone chips. I applaud the fact that you were able to get even 50% coverage. 100 on the age of your cars. Authorized repair centers are a whole other topic, on which I too have my theories, but I lack the inside knowledge to offer a qualified opinion.
Lou Trottier owns and operates All About Imports in Mississauga. A question about maintenance and repair? E-mail [email protected]by placing “Lou’s Garage” in the subject line.
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