Richard Simonds – Technical Q & A

Richard Simonds
Battery Failures, Grades of Gasoline, and Check Engine Light

Battery failures

Q I recently read in a newspaper that new-car battery failures are rising. The article stated that 44 percent more auto owners reported suffering car-battery failures this year than in 2016. Are batteries not as good as they used to be?A Car batteries are better than they were even 10 years ago. Improved lead-acid batteries, the development of gel-cell batteries and lithium-ion batteries are factors. Mercedes-Benz Cars has recently added a small supplemental battery to the main battery as a power source for the multitude of electronic devices in new cars. The problems appear to be linked to all those electronic devices – such as the Smart Keys that are part of the keyless systems used by so many luxury-vehicle manufacturers and gadgets with presets – and by short-distance driving that never gives the battery a full charge between uses.Let’s look at each of these factors separately.  With a keyless system, the car key is kept in your pocket or purse and never touched to unlock or lock doors, trunk or rear hatch. With a touch to the door or trunk/hatch handle and the mere push of a button to start and stop the engine, you are on your way. The car is regularly communicating with the key through wireless telemetry. If the key is kept nearby or left in the car when not in use (while it’s parked in your garage, for example) this wears down the car battery more than it does the key battery. Interestingly, when battery-operated key fobs were first introduced, the key initiated the communications only when it was pushed to unlock or lock the car and the key was put into a slot and twisted to the right to start the car. The same type of battery would last for three or four years. Now they have to be replaced every year – and the car notifies the driver through the instrument cluster to “Replace Key Battery.”A second issue is that so many of our devices, like the multi-adjustable seats, have presets reflecting the preferences of the owner that take a very small amount of current to maintain. However, when left for more than a month or two, such as in the car that is kept at the winter house or summer cottage, the draw is enough to drain the battery. The best solution here is to hook up one of the battery tenders that keep the battery at full charge and periodically pulse it to avoid a battery condition known as “acid stratification” where the plates in a lead-acid battery lose their ability to hold a charge.The problem of a weakened battery failing to properly hold a charge in a car used only for short-distance driving can usually be remedied by taking the vehicle out every two or three weeks for a drive of an hour or more. This simple act will fully charge the battery. What is more, beyond the benefit to the battery, a longer drive is good for the exhaust system and the car’s drive train.

Grades of gasoline?

Q I just took delivery of a 2017 C43 AMG. I also have a 2007 SLK280 and sold my 2004 C320 to buy the C43. On both of my other Mercedes-Benz automobiles, the owner's manual said to use unleaded premium, but all techs I talked to said it was not necessary. I used unleaded regular in them with no problems. My question: Is unleaded premium really necessary in the C43? A Yes! Although the knock sensor will prevent damage to the engine in Mercedes-Benz cars from the past 20-plus years, the result is that the performance and fuel mileage are reduced because of the retarded timing. Mercedes-Benz engines have been built for performance for most of their history (with few exceptions just after World War II when poor fuels were the only ones available). Before knock sensors were developed, cars would ping or knock under load (accelerating or at higher rpm) and the only way to remedy the problems was to retard the timing manually. Now knock sensors do that for us – and for the engine’s reliability and long life. One other reason to use unleaded premium is that those fuels generally have higher quality additives that keep the engine clean, extending the life of the engine by reducing the buildup of combustion residues on valves, pistons and other engine components.I have never known a Mercedes-Benz dealership technician to state that unleaded premium was not needed. However, I do not know your source for that information; I do know that it is not official policy from Daimler AG or from MBUSA. Finally, on a personal note, I have used unleaded premium gasoline from top-tier companies in all of my classics, as well as my new Mercedes-Benz vehicles, and have gone well over 200,000 miles on my engines without major problems. Good gasoline and regular oil changes and maintenance do, in my experience, pay off. I buy Mercedes-Benz for their engineering and performance and choose not to compromise either of those by saving a bit on fuel costs.

Check engine light

Q: A few years ago I started getting a Check Engine light on my dash cluster; despite the best efforts of my technician, the problem remains unresolved. Now with the car due for a smog inspection to renew the registration in my state – and a “check engine” light causes an automatic failure – I am reaching the end of my patience. I‘ve found I can use my OBD-II device to turn the check engine light off for a few hours to pass the test, but would prefer to fix the basic problem. With 251,000 miles on the car and replacement of the 12 mass airflow sensors likely exceeding the value of the car should I stop attempting to fix it?A: After consulting with Ken Adams, a dealer shop foreman and one of our experts, we went back with some specific queries. The answers, though not sufficient to confidently diagnose the issue, offer some idea of how to start checking.At about 110,000 miles, the water pump seized, so the owner’s technician replaced it, and also replaced the original temperature thermostat with a new one. Soon after that, the check engine light started coming on.To diagnose the problem, the owner purchased an aftermarket On-Board-Diagnostic II (OBDII) read-out and reset gauge. The gauge showed two codes, P0133 and P0153. These codes are associated with issues on cylinder banks 1 and 2, including faulty oxygen sensor (possibly due to heat), leaking engine vacuum or exhaust manifold, dirty mass airflow sensors, incorrect fuel pressure, or open or shorted O2 sensors.The owner stated he has replaced the catalytic converters, front and rear oxygen sensors in the exhaust system for both cylinder banks, and checked sensor wiring grounds and fuel pressure. He had been warned not to clean the mass air flow sensors in the intake manifolds because this could ruin them and cause terminal engine failure.Adams recommends that the owner and the technician make sure all the basics are correct first before either giving up or beginning to replace more components. Go back to square one to ensure that the thermostat is correct for the engine so that the engine control module will be getting correct information. Then look for poor electrical pin fit at both the oxygen sensor connectors and the corresponding pins at the ME-SFI (Motor Electronics Sequential Fuel Injection) fuel injection control module. Beyond that, there may be an issue with the ME control module itself.

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