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Each year, cars seem to get more and more complicated. Cars today might have as many as 50 microprocessors on them. Although these microprocessors make it more difficult for you to work on your own car, some of them actually make your car easier to service.

Some of the reasons for this increase in the number of microprocessors are:

Sophisticated Engine Controls
Before emissions laws were enacted, it was possible to build a car engine without microprocessors. With the enactment of increasingly stricter emissions laws, sophisticated control schemes were needed to regulate the air/fuel mixture so that the catalytic converter could remove a lot of the pollution from the exhaust. See How Catalytic Converters Work for more details.

 

The computer from a Ford Ranger

Controlling the engine is the most processor-intensive job on your car, and the Engine Control Unit (ECU) is the most powerful computer on most cars. The ECU uses closed-loop control, a control scheme that monitors outputs of a system to control the inputs to a system, to manage the emissions and fuel economy of the engine (as well as a host of other parameters). Gathering data from dozens of different sensors, the ECU knows everything from the coolant temperature to the amount of oxygen in the exhaust. With this data, it performs millions of calculations each second, including looking up values in tables, calculating the results of long equations to decide on the best spark timing and determining how long the fuel injector is open. The ECU does all of this to insure the lowest emissions and best mileage. See How Fuel-Injection Systems Work for a lot more detail on what the ECU does.

A modern ECU might contain a 32-bit, 40-MHz processor. This may not sound fast compared to the 500- to 1,000-MHz processor you probably have in your PC, but remember that the processor in your car is running much more efficient code than the one in your PC. The code in an average ECU takes up less than 1 MB of memory. By comparison, you probably have at least 2 GB of programs on your computer -- that's 2,000 times the amount in an ECU.

The processor is packaged in a module with hundreds of other components on a multi-layer circuit board. Some of the other components in the ECU that support the processor are:

Advanced Diagnostics
Another benefit of having a communications bus is that each module can communicate faults to a central module, which stores the faults and can communicate them to an off-board diagnostic tool.

This can make it easier for technicians to diagnose problems with the car, especially intermittent problems, which are notorious for disappearing as soon as you bring the car in for repairs.

This page lists the fault codes stored in the ECU for various carmakers. Sometimes, the codes can be accessed without a diagnostic tool. For instance, on some cars, by jumping two of the pins in the diagnostic connecter and then turning the ignition key to run, the "check engine" light will flash a certain pattern to indicate the number of the fault code stored in the ECU.

Let's take a look at how microprocessors and communications standards have made cars easier to build.

 

 

COMPUTER CODES for Honda Vehicles

This table may be used as a reference for interpreting your Honda vehicle's computer messages.

If codes other than these are indicated, repeat self-diagnosis. If codes reappear, substitute a known good ECM, and recheck codes. For 1985 through 1987. Note: OOOO all 4 lamps on, XXXX all 4 lamps off.

LED display

Symptom - Possible Cause for 1985 through 1987 Honda Vehicles

OOOO

Engine will not start - Check for disconnected control unit ground connector. Also check for a loose connection at the ECU main relay resistor. Possible faulty ECU.

OOOO

Engine will not start - Check for a short circuit in the combination meter or warning light wire. Also check for a disconnected control unit ground wire. Possible faulty ECU.

OOOX

System does not operate - Faulty ECU

OOXO

System does not operate - Faulty ECU

OOXX

Fuel-fouled spark plugs, engine stalls frequently - Check for a disconnected MAP sensor coupler or an open circuit in the MAP sensor wire. Also faulty MAP sensor.

OXOO

System does not operate - Faulty ECU.

OXOX

Hesitation, fuel-fouled spark plugs or engine stalls frequently - Check for disconnected MAP sensor vacuum hose.

OXXO

High idle speed during warm-up, continued high or hard starting at low temperature - Check for disconnected coolant temperature sensor connector or an open circuit in the coolant temperature sensor wire. Also faulty Coolant Temperature sensor.

OXXX

Poor engine response when opening the throttle rapidly, high idle speed or engine does not rev-up when cold - Check for a disconnected throttle angle sensor connector. Also check for an open circuit in the throttle angle sensor wire. Also faulty throttle angle sensor.

XOOO

Engine dose not rev-up, high idle speed or erratic idling - Check for a short or open in the crank angle sensor wire. Spark plug wires interfering with the crank angle sensor wire. Also faulty crank angle sensor.

XOOX

Same as above (XOOO)

XOXO

High idle speed or erratic idling when very cold - Check for disconnected intake air temperature sensor or an open circuit in the intake air temperature sensor wire. Also faulty Intake Air Temperature sensor.

XOXX

Continued high idle speed - Check for a disconnected idle mixture adjuster sensor coupler or an open circuit in the idle mixture adjuster sensor wire. Also faulty Idle Mixture Adjuster sensor.

XXOO

System does not operate at all - Faulty ECU

XXOX

Poor acceleration at high altitude when cold - Check for a disconnected atmospheric pressure sensor coupler or an open circuit in the atmospheric pressure sensor wire. Also faulty Atmospheric Pressure Sensor.

XXXO

System does not operate at all - Faulty ECU

XXXX</FONT< td>

Same as above (XXXO)

 

CODE

PROBABLE CAUSE for Honda Vehicles 1988 and later.

0

Faulty ECU (no signal)

1

Oxygen sensor or circuit.

2

Faulty ECU

3 & 5

Manifold Absolute Pressure (MAP) sensor or circuit.

4

Crank angle sensor or circuit

6

Coolant temperature sensor or circuit

7

Throttle angle sensor or circuit.

8

TDC position/crank angle sensor or circuit.

9

Crank angle sensor or circuit

10

Intake air temperature sensor or circuit.

11

No particular symptom shown or system does not operate - faulty ECU

12

Exhaust gas recirculation (EGR) failure

13

Atmospheric pressure sensor circuit.

14

Electronic air control valve (EACV)

15

No ignition output signal - possible faulty igniter.

16

Fuel injector circuit.

17

Vehicle speed sensor or circuit (VSS)

19

Lock-up control solenoid valve (automatic transmission)

20

Electronic load detector - possible open or grounded circuit in ECU wiring.

21

VTEC spool solenoid valve circuit (Civic & Del-Sol)

22

VTEC oil pressure switch circuit (Civic & Del-Sol)

23

Knock sensor (Prelude)

30

A/T control unit ECM fuel injection signal "A" (Accord & Prelude)

31

A/T control unit ECM fuel injection signal "B" (Accord & Prelude)

41

Heated oxygen sensor - heater circuit.

43

Fuel supply system circuit (except D15Z1 engine)

43

XX

45

Fuel system out of range - rich or lean

48

Heated oxygen sensor circuit (D15Z1 engine)

50

Mass airflow sensor.

61

Front oxygen sensor response slow.

63

Rear oxygen sensor circuit voltage out of range.

65

Rear oxygen sensor circuit malfunction.

67

Catalyic converter efficency low.

70

Automatic Transaxle problem.

71 through 76

Cylinder misfires

80

Insufficient EGR flow

86

Engine coolant temperature sensor circuit.

92

Evaporative emission purge valve problem.

Disclaimer:
Use this as a guide, not a Bible. These codes are assumed current through 1997. No warranties or guarantees as to correctness or fitness for use is stated or may be implied

 

 

 

 

Easier Design and Manufacturing
Having communication standards has made designing and building cars a little easier. A good example of this simplification is the car's instrument cluster.

The instrument cluster gathers and displays data from various parts of the vehicle. Most of this data is already used by other modules in the car. For instance, the ECU knows the coolant temperature and engine speed. The transmission controller knows the vehicle speed. The controller for the anti-lock braking system (ABS) knows if there is a problem with the ABS.

All of these modules simply send this data onto the communications bus. Several times a second, the ECU will send out a packet of information consisting of a header and the data. The header is just a number that identifies the packet as either a speed or a temperature reading, and the data is a number corresponding to that speed or temperature. The instrument panel contains another module that knows to look for certain packets -- whenever it sees one, it updates the appropriate gauge or indicator with the new value.

Most carmakers buy the instrument clusters fully assembled from a supplier, who designs them to the carmaker's specifications. This makes the job of designing the instrument panel a lot easier, both for the carmaker and the supplier.

It is easier for the carmaker to tell the supplier how each gauge will be driven. Instead of having to tell the supplier that a particular wire will provide the speed signal, and it will be a varying voltage between 0 and 5 V, and 1.1 V corresponds to 30 mph, the carmaker can just provide a list of the packets of data. Then, it is the carmaker's responsibility to make sure that the correct data is output onto the communications bus.

It is easier for the supplier to design the instrument panel because he doesn't need to know any details of how the speed signal is generated, or where it's coming from. Instead, the instrument panel simply monitors the communications bus and updates the gauges when it receives new data.

These types of communications standards make it very uncomplicated for carmakers to outsource the design and manufacture of components: The carmaker doesn't have to worry about the details of how each gauge or light is driven, and the supplier who makes the instrument panel doesn't have to worry about where the signals are coming from.

Smart Sensors
This technique is starting to be used on a smaller scale for sensors. For instance, a traditional pressure sensor contains a device that outputs a varying voltage depending on the pressure applied to the device. Usually, the voltage output is not linear, depends on the temperature and is a low-level voltage that requires amplification.

Some sensor manufacturers are starting to provide a smart sensor that is integrated with all the electronics, along with a microprocessor that enables it to read the voltage, calibrates it using temperature-compensation curves and digitally outputs the pressure onto the communications bus.

This saves the carmaker from having to know all the dirty details of the sensor, and saves processing power in the module, which otherwise would have to do these calculations. It makes the supplier, who is most up on the details of the sensor anyway, responsible for providing an accurate reading.

Another advantage of the smart sensor is that the digital signal traveling over the communications bus is less susceptible to electrical noise. An analog voltage traveling through a wire can pick up extra voltage when it passes certain electrical components, or even from overhead power lines.

Communication buses and microprocessors also help simplify the wiring through multiplexing. Let's take a closer look at how they do this.

Simplified Wiring
Multiplexing is a technique that can simplify the wiring in a car. In older cars, the wires from each switch run to the device they power. With more and more devices at the driver's command each year, multiplexing is necessary to keep the wiring from getting out of control. In a multiplexed system, a module containing at least one microprocessor consolidates inputs and outputs for an area of the car. For instance, cars that have lots of controls on the door may have a driver's-door module. Some cars have power-window, power-mirror, power-lock and even power-seat controls on the door. It would be impractical to run the thick bundle of wires that would come from a system like this out of the door. Instead, the driver's-door module monitors all of the switches.

Doors with lots of switches are becoming more and more common.

Here's how it works: If the driver presses his window switch, the door module closes a relay that provides power to the window motor. If the driver presses the switch to adjust the passenger-side mirror, the driver's door module sends a packet of data onto the communication bus of the car. This packet tells a different module to energize one of the power-mirror motors. In this way, most of the signals that leave the driver's door are consolidated onto the two wires that form the communication bus.

The development of new safety systems has also increased the number of microprocessors in cars. We'll talk about this in the next section.

Safety Systems
Over the last decade, we've seen safety systems such as ABS and airbags become common on cars. Other safety features such as traction-control and stability-control systems are starting to become common as well. Each of these systems adds a new module to the car, and this module contains multiple microprocessors. In the future, there will be more and more of these modules all over the car as new safety systems are added. At the 2001 North American Auto Show, we saw Volvo's Safety Concept Car (SCC), which showcased some of these upcoming safety features.

The Volvo Safety Concept Car

New technology developed for this car allows the vehicle's interior to adjust to the driver's body size and eye position. Sensors scan the precise position of the driver's eyes and then adjust the driver's seat to offer the best possible vision. The steering wheel, floor, pedals and center console also adjust to a more comfortable position for the driver.

The SCC includes active rearview mirrors and rear bumper sensors that alert the driver to approaching traffic in the car's blind spot. Rear-facing cameras also add to the driver's field of vision. Adaptive headlamps monitor the car's speed and steering wheel movements and adjust lighting accordingly. For example, at high speeds, light beams are given a longer reach. The car is also equipped with an infrared light enhancer to improve night vision.

Drivers moving outside of their lane will be warned by the SCC's remain-in-lane technology. Forward-facing cameras monitor the car's position in relation to the road's centerline and side-marker lines for 20 meters ahead of the car. If the car begins to veer out of the lane, a warning is sounded.

Each of these safety systems requires more processing power, and is usually packaged in its own electronics module. But it doesn't end there. In addition to more safety features, concept cars at the 2001 auto show were bursting at the seams with new convenience features, meaning still more microprocessors.

Comfort and Convenience
In coming years, we'll have all kinds of new features in our cars, and each of these requires more electronics modules containing multiple microprocessors. The Dodge Super8 Hemi concept car showcased some of these technologies.

This concept car has such features as wireless Internet access and voice control of many car functions, including audio, climate-control, phone and even e-mail!

The rear passengers have individual LCD touch screens so they can watch movies or access the Internet. The car has satellite radio and can play MP3 music that you transfer from your home stereo to the car while it is parked in the driveway or garage.

It seems that there is no limit to how much technology carmakers are going to pack into our cars. The addition of all these electronic features is one of the factors driving carmakers to increase the system voltage on cars from the current 14-V system to a 42-V system. This will help provide the extra power these modules require.

From web site

http://www.howstuffworks.com/car-computer.htm

 

The hyperlinks will take you back to the original web site.

The article has been copied here just in case the web site is not up.

 

 

 

 

 

 

 

 

 

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