Introduction of vehicle emissions control strategies

5.1.4 Introduction of vehicle emissions control strategies

To meet the ever increasing but justifiable and ‘wanted’ need of vehicle emissions control legisla- tion, vehicle manufacturers were forced to invest heavily in the research and development of Vehicle Emission Control Strategies. Building upon the foundation laid by PCV, the two-way and three- way catalyst, manufacturers further developed emissions control hardware. Such systems included exhaust gas re-circulation, secondary air injection, fuel tank canister purge, spark timing adjustment, air/fuel ratio control biasing, fuel shut off under

Figure 5.3 Malfunction indicator lamp symbols

64 Advanced automotive fault diagnosis tend to use the engine symbol on an orange

background. When the fault occurs the system stores a diag- nostic trouble code (DTC) that can be used to trace and identify the fault. The system will also store important information that pertains to the operat- ing conditions of the vehicle when the fault was set. A service technician is able to connect a diag- nostic scan tool or a code reader that will commu- nicate with the microprocessor and retrieve this information. This allows the technician to diag- nose and rectify the fault, make a repair/replace- ment, reset the OBD system and restore the vehicle emissions control system to a serviceable

Figure 5.4 New mass airflow sensor (Source: Bosch)

status. As vehicles and their systems become more complex, the functionality of OBD is being

within the cylinder. It may be that tailpipe emis- extended to cover vehicle systems and components sions are likely to rise beyond legislated limits. that do not have anything to do with vehicle emis- Also the MAF sensor is used by other emis- sions control. Vehicle body, chassis and accessories sions control systems on the vehicle – now that such as air conditioning or door modules can now its input is unreliable it follows that those sys- also be interrogated to determine their service- tems are no longer working at their optimum levels ability as an aid to fault diagnosis. and may not work at all. This is the reason for the

malfunction indication lamp (MIL) illumination,

which says, in as many words: Whilst driving, a vehicle owner observes that the

5.2.1 OBD scenario example

An emissions control system/sub system or vehicle’s engine ‘lacks power’ and ‘jumps some-

component has become unserviceable! times’. This is a problem often faced by techni-

Visual inspection of the MAF sensor reveals that cians in that customers often have no engineering

it has become damaged beyond repair and needs or automotive knowledge and use lay terms to

replacing. This is carried out, the technician describe what is happening with a very complex

clears the DTC from the OBD system memory, system. The driver does however report that the

resets the system, and a short test drive later the MIL has been illuminated.

diagnostic scan tool confirms that the DTC is no The technician connects a scan tool that can

longer present. The road test also confirms that communicate using an industry standard com-

the previous drive issue is no longer apparent. munications protocol. The OBD code memory is

checked and data is presented in a way that also conforms to a standard. DTC P1101 with the