I had a test done at local auto-parts store that showed a code of PO138. They told me this indicates a problem with the oxygen sensor. I replaced the oxygen sensor and the light never went out.
I contacted the mechanic that services my vehicle when I can’t, and he said codes don’t always indicate what is wrong. Now what do I do?
A: Computer fault codes can sometimes be misleading, even to the best technician.
There is a specific troubleshooting procedure that needs to be followed for correct diagnosis and repair. The sensor will never work correctly if the wiring to and from the sensor has a problem. A technician will usually check for proper voltage and grounds to the sensor. Even a new sensor with a faulty ground circuit will not function properly.
Q: I have a 10-year-old Toyota and the high-beam bulbs have a much shorter life than the low-beam bulbs. This doesn’t make sense, since I only use the high-beams on my car maybe 10% of the time. Do you have any idea as to what is going on?
A: The first test that needs to be performed is to measure the voltage at the bulb. Higher than normal voltage will certainly cause short bulb life.
You didn't mentioned what model Toyota you have, but some Avalon models have had this problem, and it was remedied with a new bulb and headlight housing.
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Q: I recently read your answer about octane rating and possible damage to a Mercedes from using the wrong gas. My Acura states in the owner’s manual — and on the gas door — that 91 octane fuel is recommended.
My partner and I argue over this (we are lawyers who argue over everything). I don’t think it is necessary and he says it is. This bothers me for two reasons: it states recommended, not required (I take things very literally) and there is no such thing (at least in my area) as 91 octane. So he uses 93 octane, which is more expensive.
A: AAA engineers completed a study that concluded that in cars that recommend premium fuel, there may be a slight horsepower/fuel economy benefit of 1% to 3%. Although, in most cases, there was no difference.
Unless you are towing a heavy trailer on hilly terrain or a competitive racer, I have found no difference in performance and fuel economy in day-to-day driving using 87 octane fuel when premium fuel is recommended.
Years ago, when premium fuel only cost 10 cents more than regular fuel, it made some financial sense. Today, with premium fuel costing 20 to 60 cents more than regular, any mileage gains are lost to the extra cost of the fuel.
One note of caution — for any vehicle owner — if your vehicle owner’s manual "requires" premium fuel, use it. If it is "recommended," our studies show that for most drivers it is just money wasted.
Q: I keep seeing plenty of advertising about electric cars and, with the recent announcement from the Biden administration about charging stations and infrastructure, it makes electric sound better.
Would you buy an electric vehicle? Do you think there will be enough electricity to power electric cars in the near future?
A: Regarding electrical capacity, some reports show that by the year 2050 the electrical grid demand will increase 38% due to electric vehicle recharging.
To offset this, off-peak vehicle charging will be necessary to limit stress on the grid. In this scenario powerplants would produce electricity to charge vehicles when they are typically idle (late night).
Hopefully, as wind, solar and other future technology replace high-polluting powerplants, charging electric vehicles will be part of that equation. In addition, electric vehicles could also help when electric supply is in high demand, since they can store electricity and transfer it back to the grid.
Would I buy an electric car? Yes, although at this point I’m not sure it could be my primary form of transportation.
I have evaluated the Ford Mach-E and Chevy Bolt and found them to be very usable. I recently drove the Mazda MX-30. Though it was fun to drive and very cool-looking — and with only a 100-mile range — it was not for me.
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John Paul is the AAA Northeast Car Doctor. He has more than 40 years of experience in the automobile industry and is an ASE-Certified Master Technician. Write to John Paul, The Car Doctor, at 110 Royal Little Drive, Providence, RI 02904. Or email jpaul@aaanortheast.com and put “Car Doctor” in the subject field. Follow him on Twitter @johnfpaul or on Facebook.