Eeprom

An electrically erasable PROM works in a similar way to the EPROM, the main difference is that the memory can be erased and reset by a special charge pump circuit that is controlled by the microcontroller according to the working program of the ECM. The RAM, or random access memory, is the section of memory that is used for temporary storage of data while it is being worked on. It must be the type of memory that can be written to (i.e. data is placed in it) and read from (i.e. data is taken...

Canl

The CAN-H wire switches between 2.5 and 3.5 V and the CAN-L wire switches between 2.5 and 1.5 V. When CAN-H and CAN-L are at 2.5 V, there is no voltage difference between them and this represents computer logic 0. Computer logic 1 is created when there is a 2 V difference between the two wires as happens when CAN-H is at 3.5 V and CAN-L is at 1.5 V. In order to provide further insight into the way in which vehicle systems are networked it will be helpful to consider the following details of a...

461 Vacuum Pumps And Gauges

A vacuum pump and gauge of the type shown in Fig. 4.17 can be used for a range of purposes, such as checking a MAP sensor performance, EGR valves and other devices that are vacuum operated. Fig. 4.15 Part of the procedure for use of the Bosch KTS 500 instrument Fig. 4.15 Part of the procedure for use of the Bosch KTS 500 instrument When used to check the performance of a manifold absolute pressure sensor, or an exhaust gas recirculation valve, the vacuum pump is used to replace the manifold...

862 Secondary Air Injection

The aim of secondary air injection into the exhaust system is to reduce CO and HC emissions in the period after start-up and during the warm-up phase. The extra oxygen that is introduced assists the catalytic converter with the oxidation process. Figure 8.17 shows a system used by Volvo cars. Fig. 8.17 Secondary air injection system Fig. 8.17 Secondary air injection system With reference to Fig. 8.17, the solenoid valve (4) is under the control of the ECM, as is the relay (2) that provides the...

633 Pulse Width Modulated Injectors

Pulse modulated (power control) injectors have a high initial current to provide rapid opening of the injector valve. After the initial pulse, the ECM switches the earthing transistor on and off at high frequency. This permits the injector to remain open for the required time whilst preventing the circuit from overheating. Figure 6.7 shows the type of oscilloscope trace that should be obtained from this type of injector. Fig. 6.7 Oscilloscope trace for a pulse width modulated injector Fig. 6.7...

412 Obd Ii Type Diagnostic Equipment

Much of the diagnostic capability that is known as OBD II has been in use for some time. The main effect of the OBD II legislation seems to have been to focus attention on the desirability of standardization, particularly in the areas of means of access to diagnostic data on vehicle systems and the availability of supporting documentation. This means that some of the techniques described under this heading will, in some cases, be available on non-OBD II systems. Firstly the principal features...

The Computer ECM

Computer System Transmission

Whilst vehicle computers (ECMs) are not made to be repaired in garage workshops, there are certain factors that require technicians to have an appreciation of computer technology. For example, diagnostic trouble codes (DTCs) are an important part of fault finding and DTCs are stored in the computer memory. The means by which these codes are read out varies from vehicle to vehicle and it is helpful for technicians to understand why a procedure for reading DTCs on one vehicle may not work on...

Common technology

The aim of this chapter is to review a number of computer controlled vehicle systems that are in current use and to make an assessment of the technology involved that is common to a range of systems. It is this knowledge that is 'common' to many systems that enables a vehicle technician to develop a 'platform' of skills that will assist in diagnostic work across the spectrum of vehicles, from small cars to heavy trucks. Subsequent chapters concentrate on aspects of the technology that enable...

1111 Spill Control

Rotary Type Injection Pump

Figure 1.34 shows a cross-section of a rotary-type fuel injection pump. The high pressure pump chamber that produces the several hundred bars of pressure Spill Control Valve Fuel Temp. Sensor Fig. 1.33 Computer controlled diesel engine system Fig. 1.33 Computer controlled diesel engine system Fig. 1.34 Rotary-type fuel injection pump Fig. 1.34 Rotary-type fuel injection pump that operate the fuel injectors, has two outlet ports. One of these outlet ports connects to the solenoid-operated spill...

Test Instruments Connected To These Pins

When the box is inserted it permits electrical access to most elements, such as sensors actuators and circuits, that make up the system that is being controlled by the ECM in question. A major advantage of the breakout box is that it permits resistance, continuity and dynamic tests of sensor and actuator circuits to be performed more easily because it overcomes the need to access the contacts inside the harness to ECM connector. The breakout box's electrical connections are numbered to match...

Diagnostic tools and equipment

This chapter covers the types of tools and equipment and other aids that are available to assist technicians to perform accurate and efficient diagnosis and repair of automotive systems. It is not intended to be a catalogue, because there is a large number of companies that make and supply equipment. Addresses of several of these companies are given in the Appendix. Where a particular make of tool has been selected as a case study it is because the makers have supplied the information that...

Selfdiagnosis and fault codes

Whilst a computer controlled system is operating normally, the processor is constantly monitoring the electrical state of input and output connections at the various interfaces of the ECM. This monitoring (reading) of the inputs and outputs occurs so that the instructions that the computer processor has to perform, such as to compare an input value with a programmed value stored in the ROM, means that the ECM is ideally placed to 'know' what is happening at many parts of the system that is...

Acknowledgements

Thanks are due to the following companies who supplied information and in many cases permission to reproduce illustrations. Robert Bosch Ltd Mr Richard Clayton - Garage equipment dept. Rover Car Company Society of Automotive Engineers, Inc. Reprinted with permission from Special thanks also to Shirley and to Phil Handley who persuaded me that the effort was worthwhile, especially when the going was hard.