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ABCs of Car Tech: Back to basics

Welcome to the first installment of a new feature that where we will be explaining the whats, whys, and hows of car technology.

Wayne Cunningham/CNET

The vehicle above is an FWD PHEV with a DOHC ICE rated at 98BHP and 87MPGe. Some of you know exactly what all of that means, but many will need a translation.

Welcome to the first installment of a new feature that I like to call the ABCs of Car Tech. Here I will be explaining the whats, whys, and hows of car technology. This week, I'm starting by defining some basic and common abbreviations used when talking about cars.

ICE: Internal combustion engine

Air and fuel (usually gasoline or diesel) go into one end and hot exhaust gases come out of the other. Somewhere along the way, an explosion is harnessed to create the mechanical energy that turns the drive wheels of most vehicles on the road today. This is the internal combustion engine that is named after the explosion of fuel and oxygen that happens within it. ICE is also used as an abbreviation for in-car entertainment, which we'll discuss in a later edition of the ABCs of Car Tech.

The Nissan Leaf NISMO RC shares little more than than its lithium ion battery pack and name.
The Nissan Leaf NISMO RC shares little more than than its lithium ion battery pack and name with the standard Leaf. Nissan

EV, HEV, PHEV, RE-EV: Electric, hybrid electric, plug-in hybrid electric, and range extended electric vehicles

Fully electric vehicles (EVs) use an electric motor or motors powered by batteries or fuel cells to motivate a vehicle without creating tailpipe emissions because, well, there's no tailpipe. Hybrid electric vehicles (HEVs) use their electric motor to augment an ICE, increasing fuel economy by recapturing energy lost when braking. Plug-in HEVs (PHEVs) can be plugged in to draw electricity from the grid, increasing their electric-only range beyond that of standard HEVs. Finally, range-extended EVs (RE-EVs) are essentially full EVs with the addition of a small gasoline range extender--when the battery's range is depleted, the range extender fires up and generates electricity to complete the trip. Unlike HEVs and PHEVs, an RE-EV's gasoline engine is unable to directly motivate the wheels.

FWD: Front-wheel drive

When torque from the engine is used to spin the wheels on a vehicle's front axle (ahead of the driver) the vehicle is known as FWD. FWD vehicles are typically more stable in slippery conditions because the engine/transmission combo (the heaviest parts of most cars) sits atop the drive wheels, pushing them into the ground with its weight. FWD cars also react to slip most commonly with progressive understeer, which is favored by the average driver because of its predictability and ease of correction.

Corvette Z06
The RWD configuration is the best setup for epic burnouts, as I illustrate here with the Corvette Z06. Josh Miller/CNET

RWD: Rear-wheel drive

A rear-wheel drive vehicle send its engine's torque to the wheels on the rear axle, often by way of a driveshaft that runs down the vehicle's spine. Performance drivers favor RWD vehicles because this configuration splits steering and acceleration duties between the front and rear axles, allowing the vehicle to take better advantage of available grip. In the hands of an experienced driver, an RWD can begin to accelerate out of most turns earlier and with more available traction. In the hands of an inexperienced driver and without the aid of traction and stability control systems, RWD systems can prove to be a handful at speed.

Extra credit: Most cars sold today are designed as FF (front engine, front-wheel drive) vehicles, but many sports coupes, sedans, and larger trucks utilize an FR (front engine, rear-wheel drive) configuration. Some of the most nimble sports cars available use an MR (midengine, rear-wheel drive) setup, but the Porsche 911 series still champions the RR (rear engine, rear-wheel drive) and R4 (rear engine, four-wheel drive) layouts. No vehicle in mass production uses the oddball RF (rear engine, front-wheel drive) configuration.

AWD, 4WD: All-wheel drive or four-wheel drive

All-wheel-drive systems seek to maximize traction for acceleration by splitting the power delivered to all four of the vehicle's wheels. How this torque split is accomplished and how much power goes where varies wildly from model to model and from manufacturer to manufacturer. See our previous feature on all-wheel-drive systems for more details on the differences between the various manufacturers' implementations of the technology.

2011 Toyota Prius
There's an obvious joke here about the Prius being next to 'MPG' in the dictionary. Toyota

MPG: Miles per gallon

The number of miles that a vehicle can travel on a single gallon of fuel is probably the most widely used measure of vehicle efficiency in the United States--most likely because a low score here immediately hits the owner where it hurts the most: in the wallet and at the pump. The Environmental Protection Agency (EPA) provides three estimated scores for each vehicle that it tests: one for a city driving cycle, one for the highway, and a third combined score that should reflect real-world expectations on a mixed driving cycle. As the saying goes, "Your mileage may vary."

In other parts of the world, the liters per 100 kilometers (l/100km) metric is used to measure fuel economy and, in areas where vehicles are taxed on emissions, efficiency is also measured in grams per kilometer (g/km) of CO2, hydrocarbons, and NOX.

BHP: Brake horsepower

We don't often use the term brake horsepower in the States--in some circles, this is what's known as crank horsepower but more commonly simply "horsepower" will do. BHP measures the power output by an engine, measured at its flywheel or crankshaft. This is the number quoted by most manufacturers in their promotional materials. The problem with quoting BHP is that it doesn't take into account friction and mechanical losses of the transmission and drivetrain.

WHP: Wheel horsepower

This is the amount of power that your car actually puts to the road at its drive axle(s). Typically, this can be as little as 10 to 15 percent lower than the quoted BHP for the best FWD and RWD vehicles, but can also be as high as a 25 percent loss for economy cars and even more so for heavier, more complex all-wheel-drive systems. Measuring WHP requires strapping the vehicle to a dynamometer (or dyno, for short) where the vehicle's wheels turn large drums that simulate a road and measure actual power output across the RPM range.

RPM: Revolutions per minute

Regardless of whether they push pistons, spin a rotor, or convert electricity into torque, all automobile engines end up spinning an output shaft at some point. RPM measures the engine speed or how quickly the output shaft is spinning. If the RPMs are too high, the engine can be damaged. If the RPMs drop too low, ICEs can stall and stop. Keeping an eye on engine speed is of particular importance when changing gears on vehicles equipped with manual transmissions.

Extra credit: Automakers and enthusiasts sometimes refer to the type of transmission with the xMT or xAT designations, where 'x' refers to the number of forward gears and MT and AT refer to manual and automatic transmissions, respectively. So, a 6MT is a six-speed manual transmission and a 4AT is a four-speed automatic.

The VW Golf GTI is equipped with the DSG, an automated manual that shifts very quickly. Josh Miller/CNET

DCT: Dual clutch transmission

This automatic transmission type actually combines a two separate gear sets for even and odd gears with two computer-controlled clutches that switch between them. DCTs combine the best attributes of manual transmissions (more efficient power transmission, more direct engagement) with shifts that are faster than standard automatic transmissions. Different automakers have unique names for this technology. For example, Volkswagen calls its system DSG, Porsche's system is PDK, and Mitsubishi calls its the Twin Clutch SST. We'll be revisiting just how these DCT gearboxes work in a later edition of the ABCs of Car Tech.

SOHC/DOHC: Single/dual overhead camshaft(s)

A camshaft is a rotating shaft in the engine's cylinder head that features raised lobes that cause the valves atop each combustion chamber to open and close to allow clean air in and spent exhaust out. The SOHC and DOHC designations refer to the number of camshafts present. I should note that the number of cams is typically counted per cylinder bank. So, a DOHC inline engine features two camshafts, while a DOHC V-oriented or a horizontally opposed boxer engine will have four. SOHC engines are cheaper to manufacture, but DOHC setups can be more efficient and powerful thanks to their ability to independently set intake and exhaust timing.

ECM, PCM, or ECU: Electronic/powertrain control module or emissions control unit

If your car were a living organism, the ECM would be the brain (or at least the cerebellum and medula oblongata). This specialized computer is controls every parameter of the engine and emissions systems, the heart and lungs in this metaphor. When you press the accelerator pedal, the ECM decides how much fuel gets squirted into the combustion chamber, when an how long the intake and exhausts valves open, when the spark fires, and, on vehicles equipped with ETC (see below), how much air gets sucked into the intake manifold. It does all of this by monitoring dozens of readings from dozens of sensors hundreds of times per second.

CEL: Check engine light

Remember all of those parameters that your ECM is monitoring for your engine and emissions systems? When one of those parameters comes back outside of the acceptable range (or doesn't come back at all), the vehicle will notify you, the driver, by illuminating the Check Engine Light. At this point, you can either take your car to a mechanic, who knows what he or she is doing, or you can check out the next two entries in this list.

OBD-II port on a Ford Focus
Every car sold after 1996 has one, but what does that OBD-II port under your steering wheel do? Antuan Goodwin/CNET

OBD-II: On-board diagnostics (generation II) port

Every vehicle manufactured after 1994 is equipped with an onboard diagnostics port. By plugging the right sort of device into this port, a technician or enthusiast can view and record all of the parameters monitored by the ECM. In the case of an illuminated CEL, the OBD-II port will also report one or more DTCs.

DTC: Diagnostic trouble code

A diagnostic trouble code (DTC) is an alphanumeric code unique to a specific issue that the ECM has noticed. Values exist for everything from a misplaced or improperly locked fuel cap to major faults with the emissions systems. Code systems vary by manufacturer, but can be easily researched and cross referenced online and are cleared either automatically by fixing the problem (closing your gas cap) or manually using most OBD-II code readers.

ETC: Electronic throttle control

When I first started wrenching on cars, the gas pedal in the footwell was physically connected to the engine's throttle body with a cable. If you pushed the pedal to the metal, the throttle opened all of the way up. If you went half way, you got half throttle. These days, a sensor connected to the pedal sends an electronic signal to the ECM, which in-turn decides how much air to let into the engine for optimal acceleration and efficiency. This is how electronic throttle control (or drive-by-wire) works.

The Ford Focus' EPS system enables the vehicle's computers to take over steering for automatic parallel parking. Josh Miller/CNET

EPS: Electronic power steering

Electronic power steering systems multiply the energy exerted by the driver on a vehicle's steering wheel using an electric motor attached to the vehicle's steering rack. All power steering systems make vehicles easier to handle at low speed, where unassisted steering systems would require a massive amounts of effort to turn, but electronic power steering systems have the advantage of being both lighter and more efficient than traditional hydraulic power steering systems. EPS systems can also be taken over by the vehicle's computers for safety and convenience features such as automatic parking and lane keep assistance.

That's it for this very basic first installment of the ABCs of Car Tech. If there's a term that you think that I missed, don't worry, there are plenty more to come. If you've got an aspect of car tech that confuses you, send me an e-mail at or sound off in the comments section below and you could see it explained in a future installment of the ABCs of Car Tech.

Next week, we'll be discussing popular tuner terminology and lingo.