Published On August 1, 2019
A vehicle with a stop/start system is coming to your bays or might already be there.
These systems can improve fuel economy by 5-12% based on the driving habits of the customer. For your shop, it is indispensable to figure out what is different on these vehicles and how it might modify your diagnostic approach.
With improved engine position sensors and gasoline direct injection, the Engine Control Module is capable of doing a neat trick. Since the system knows the location of the piston and valves, it can use the fuel injector and spark plug in the cylinder to “nudge” the engine over to make life easier for the starter. The system will search for cylinders that are on a downward stroke. When the engine needs to start, a small amount of fuel will be injected and ignited to make the engine moving.
When the engine halts so do the alternator. The battery must run the Heating Ventilation and air conditioning, infotainment and other systems with little or no interruption. Most stop/start systems utilize a deep cycle aggregated glass mat battery (AGM). This type of battery demands various testing approaches and shop chargers. Some systems use a second battery to deal with non-starter loads hence the customer doesn’t notice any disruption to HVAC or audio.
When the engine ceases, the transmission pump behind the torque converter stops turning and line pressures fall. Stop/start vehicles use an electric pump and maybe an accumulator to keep the transmission fluid under pressure. If the pump goes out of action, the transmission will slam into gear when the engine is started.
Managing the temperature in the car is crucial. Baking a driver for saving money on gas would not be the best choice. When the engine stalled, the HVAC system is looking at the outside and cabin temperatures to determine whether the engine expects to be started to drive the A/C compressor or if the auxiliary coolant pump requires to be turned on to pump hot coolant to the heater core.
Don’t regard the brake pedal position sensor as just a switch. Stop/start vehicles measure brake pedal travel and force therefore by the time the driver has moved their foot from the brake pedal to the gas one, the engine has switched on.
Imagine if a stop/start car cut off and once the driver lifted her foot from the brake pedal the engine did not restart. To prevent this from happening, stop/start systems have three or more ways to measure the condition of the battery. The first measure is voltage coming from the battery. Second, the system measures current and loads at the battery with coil winding like a current clamp on the positive battery cable. Third, most systems measure the temperature of the battery directly or through data PIDs for under-hood temperatures.
With this information, the ECM can conclude if a stop/start cycle is possible. It is also a very good indicator of the health of the battery. Many systems will turn on a battery life indicator if it detects a low battery.
High-end stop/start systems use a large generator/motor combo between the engine and transmission to turn the engine and generate power. But, the majority of systems are using a starter that looks a lot like a conventional starter.
These starters operate the same way but with some critical internal differences. The first thing you will notice is that the gear on the starter is larger and the gear reduction system is lower. This allows the starter to turn slower, which decreases wear on the brushes and bearings. Also, the armature and bushes are updated to raise the longevity of the starter.
Some stop/start vehicles are using the supplementary water pump to move the coolant in the block, head and heater core to ensure the engine will not be heat soaked from the coolant not moving.
A Stop/start system is not just one module. It is a complex strategy among many modules sharing information from cabin humidity to crankshaft position to determine what happens at the next stoplight. It means that serial data communication bus and electrical diagnostics will be much more important for technical staff in the years to come.
New oil standards from the OEMs, API(American Petroleum Institute) and ILSAC(International Lubricating Oil Standards and Approval Committee) have new inspections to help measure if the engine oil protects components such as the camshaft, crankshaft, and the bearings during stop/start operation. Most of these tests check out how the oil attaches to the surfaces. Besides, engine manufacturers are using electric pumps, accumulators, and valves to keep the oil moving and prevent too much oil from draining into the pan. Turbocharged engines that have a stop/start system have a pump that circulates oil to avoid coking up in the housing and lines.