Governments have recently become interested in air quality and therefore emission related faults in vehicles. Regulations have been passed that require engine management systems to record any problem that is likely to adversely effect emissions, and to store the fault and the distance travelled since it was detected. The information must then be available to any compliant diagnostic tool. To ensure that vehicles comply with the above regulations, a standard has been developed called European On Board Diagnostics (EOBD). This is a part of the European standard, stage three emissions legislation, which becomes Law from 01\01\2001.
For a vehicle to be sold in any EEC member country it must first pass a vehicle type approval test. To pass this test after 01\01\2000 all vehicles with petrol engines must be fitted with the EOBD system (European directive 98/69/EC). Vehicles that have already passed the test can continue to be sold until 2001, when they too must comply with the standard. The deadline for both diesel and LPG (liquid petroleum gas) is 2003. For a more detailed history of OBD1, OBD2 and EOBD including the various legislative requirements go to 'Detailed History'.
When attempting to pinpoint a fault in any vehicle system, the technician has to go through three essential steps:
The ability to perform these processes effectively and efficiently is one of the most significant challenges facing technicians, workshops, and vehicle manufacturers today.
Traditional ways in which we can collect data include chatting to the driver, road testing, visual inspection, and using engine and emission analyser. The early 1980's saw the introduction of On Board Diagnostics (OBD), an in-built method of monitoring a vehicle system such as an engine management, brake or other control system. This brought two main benefits:
At the present time OBD abilities are not standard, but vary according to vehicle system and age. Therefore, the number, type and validity of the tests that can be carried out is primarily determined by that system's Electronic Control Module (ECM). Early OBD systems were very limited, most technicians who have worked with such systems will have come across a vehicle that has an obvious symptom, but reveals nothing through OBD tests. Worse still is the fact that early systems often gave the impression that a circuit was faulty, when in fact the circuit could not work because of a fault elsewhere.
The three methods described below (Automatic Fault Recognition and Coding, Output of Live System Information and Driving Actuators) need to be used at the correct times in a diagnosis. This timing will depend upon the symptom exhibited, but generally the following testing pattern should be used for most complicated diagnostics.
Diagnostic Trouble Codes should be read, written down and erased after a visual inspection of the engine, brake or other control system area. The erasing of the codes will allow you to see if they come back later.
Conventional analysis (such as with an engine analyser or multimeter) should be carried out next. This step is necessary to ensure that those components that are not checked by the OBD system are in good working condition.
The codes should now be examined again to see if they have returned.
Live readings should be used if no fault has been detected, or if a circuit fault is suspected, as this will allow you to carry out your own diagnosis.
Where a circuit or component is not working, start the circuit analysis off with an OBD actuator test.
With the ignition on, or engine running, the ECM monitors some or all of the circuits that are connected to it. Current is passed through these circuits and voltages are measured against pre-programmed parameters. If the readings taken are outside of these parameters, the ECM can log a Diagnostic Trouble Code, which is specific to that fault. There are several problems to be aware of:
When a fault is detected, its status, i.e. present fault, past fault, or intermittent fault may also be recorded. The ECM may now adopt a Limited Operation Strategy (LOS or limp home mode), if one is available and it would improve the operation of the vehicle in some way. There are three common strategies: value substitution, circuit substitution and ignoring the signal.
As already mentioned, the ECM may not always be able to detect a fault, and where it can, it simply provides data. The diagnosis is up to the technician. Most modern systems, therefore, also have the ability to provide data about what is happening in the individual circuits at the time. This allows the user to perform their own diagnosis of the symptoms or data.
The ability of the ECM to operate a circuit on the request of the technician allows for simple visual or audible confirmation of circuit continuity and basic component function. Although it can be excellent if you need to tell whether the fuel pump is working when it is in the fuel tank, it does not of course mean that the fuel pressure is correct.
Access to the data in the OBD system is gained through a diagnostic socket. The lack of standardization in Europe has meant that the socket is specific to the manufacturer, and could be located anywhere on the vehicle. Equipment, therefore, has had to be constantly updated to connect and communicate with newly emerging systems.
EOBD compliant vehicles must be fitted with a standard connector, to be located in a standard area of the vehicle. They must be capable of talking one of the approved EOBD languages (150 9141, J1850, Keyword protocol 2000 or Controller Area Network) and give access to a minimum quantity of data. The abbreviations used have been standardize and the driver must be warned that there is a fault with the system. This means that any competent garage/technician can, by using a suitable diagnostic tool, quickly locate, connect to, and use this diagnostic approach. Any faults reported will be done so in a consistent way regardless of the vehicle make, model and test equipment used. EOBD is a far more sophisticated monitoring system than OBD systems. It uses a 'map' of expected sensor inputs based on engine operating conditions, and components are empirically calibrated to the system. This means that replacement parts will need to be of high quality and may need to be specific to the vehicle and model.
Note: Unlike the American OBD II standard, EOBD does not monitor evaporative emissions from the fuel tank.
EOBD checks are also likely to become part of the annual MOT test, either alongside or integrated into the emissions test. Any vehicle with the MIL illuminated or with any recorded faults, including intermittent faults, will fail the test. The MIL will be located in the instrument cluster and, under normal operation, it should come on with the ignition and extinguish once the engine is started. If a fault is detected that will significantly effect emissions, the lamp will be illuminated to alert the driver. If the lamp flashes, it indicates a misfire that may cause damage to the catalyst. The vehicle should be checked as soon as possible in both cases. It is expected that it will also become an offence to drive a vehicle with the warning lamp on.
The first time a fault occurs, the system will not illuminate the MIL. Data about the fault will be stored along with information such as:
This gives the technician the details relating to a particular fault necessary to make an accurate diagnosis.
If a fault is not re-detected within the next three trips the MIL will be switched off. After this, faults that do not reoccur are deleted from the memory after a fixed number of warm up cycles.
Once a repair has been carried out, checks will need to be made to ensure that the system is happy with the work. Experience from the USA has shown that the new monitoring systems are so sensitive that the ECM may fail replacement components if they are not exact equivalents of the manufacturer's original.
The ECM will start a drive cycle as soon as the engine is started (from hot or cold) and ends when the engine is switched off. The drive cycle should include a warm up cycle. The EOBD drive cycle will be similar to the one used in OBD II in America. A complete drive cycle should allow the system to perform diagnostics on all areas and to run all monitors. For the technician or the EOBD system to perform a full drive cycle, all of the following conditions will need to be met:
Obviously as this cycle is very complex it may take several trips to complete.
On the Ford EEC-IV EOBD system, for example, the warm up cycle is completed when the coolant temperature has both risen by 23°C and exceeded 71°C.
A trip, like a drive cycle, is commenced when the vehicle is started, hot or cold, and ends when all the monitors have been completed. This process can take place over a number of drive cycles.
This is the variation in oxygen content as measured by the oxygen sensor. It is used to control the amount of fuel injected.
As for short-term fuel trim but recorded over a predetermined number of seconds in order to apply a permanent correction factor.
Some vehicle manufacturers use the crankshaft sensor signal in the monitoring of misfires. The crankshaft rotational speed increases during the power stroke of each cylinder and the ECM monitors the pattern of these speed increases via the signal from the crankshaft sensor over several engine revolutions. Irregularities in this acceleration pattern indicate that a misfire has occurred.
Misfires that are likely to cause overheating of the catalyst will result in a flashing MIL, these are 'type A' misfires. Misfires that are likely to cause an increase in emissions will result in the MIL being illuminated, these are 'type B' misfires.
EOBD requires a second oxygen sensor to be mounted downstream of the catalytic converter. The job of this sensor is also to monitor the mixture strength in order that the ECM can judge the effectiveness of the catalyst. The frequency of the signal is compared to that of the pre-catalyst sensor and if the signals are similar, the catalyst is inefficient. Of course, this comparison can only be achieved under certain conditions, the engine will need to be warm and the vehicle must be running in closed loop mode.
Low tension ignition system, crankshaft sensor, knock sensor.
Fuel tank level, fuel pump relay, injection circuit, mass air flow sensor, throttle position sensor, manifold absolute pressure sensor, coolant temperature sensor, intake manifold temperature sensor, camshaft sensor.
Idle air control valve, intake manifold runner control valve.
The ECM memory, air conditioning, transmission oil temperature and cooling fan circuits.
For the vehicle connector to comply to the EOBD regulations, the connector must be mounted in the driver compartment of the vehicle, preferably between the steering column and the centre line of the vehicle, and should be easily accessible from the driver's seat. Access to the connector must be possible without the need for any tools to remove covers or barriers. The connector should be located so as to permit a one handed or blind insertion out of view of the vehicle occupants, but visible to a crouched technician.
Both the vehicle and test equipment connectors should be capable of containing 16 pins, the vehicle connectors pins should be female and the test equipment male, and both should be 'D' shaped (J1962).
Pin 16 of the vehicle connector is used to provide a permanent battery positive supply and pin 4 a ground to power up the test equipment. Pins 2, 5, 6, 7, 10, 14, and 15 may be used for communication between the ECM and test equipment, depending on the protocol in use on the vehicle. Pins 2 & 10 are allocated to the EOBD communications, Pin 2 +ve and Pin 10 -ve. Pins 6 & 14 are allocated to CAN_High and CAN_Low respectively. Pins 7 & 15 are allocated to 'K' & 'L' lines respectively. Vehicle manufacturers will use differing combinations of these pins, but test equipment must use all of the above pins to ensure all protocols can be used. See the Pintable and/or Wiring Diagram.
The test equipment must be capable of providing all of the following basic functions:
Once the test equipment has been connected to the vehicle and powered up it automatically interrogates the ECM to establish which of the communication protocols the vehicles uses. This process does not require any user input. When the protocol has been established the user will be given the choice of what data they wish to display.
The process of accessing any stored DTCs takes place in two steps:
The purpose of this function is to allow access to any data values present at the time of test, including analogue and digital inputs and outputs and any system status information. The ECM will then make available for display the last data value determined by the system for the various sensors and actuators fitted. All data values displayed will be actual readings from the sensors, not default or substitute values.
This function allows the user to access data relating to stored DTCs. This data will have been stored at the time the sensor or actuator fault occurred and will provide extra information concerning the system operation at that time. The data transmitted from the ECM will be actual sensor readings and not default or substitute values.
The EOBD scan tools must be capable of clearing all stored codes and any related freeze frame data from the memory.
EOBD is similar to the OBD II that is used in the USA but has a few differences. Feedback from the use of this system has thrown up some very conflicting views, with some people singing the praises of the system and others saying that it has made diagnosis harder - technicians do not know how to properly use the information retrieved from the system, or they have been given incorrect information from technical support groups. Several reports have stated that the skill level of the technician using the equipment needs to be higher than before in order to find the cause of problems, especially intermittent ones, which people are still finding difficult to diagnose. The biggest concern with the system is the misfire monitoring. Many misfires that are illuminating the MIL are being caused by basic engine mechanical faults that repair technicians are overlooking. This is leading to unneeded replacement of components such as spark plugs, leads, distributor caps, ignition coils, etc. before the problem is correctly diagnosed. On top of this, the system has been designed to pick up very small misfires that may appear to be have no symptom as the vehicle driver cannot feel them, and they are very difficult to pin down to any fault. Again, a good understanding of basic engine diagnosis is needed to find the true cause.
Training has also been highlighted as a very important factor in order to be able to understand the information given by the system, as well as already having a good knowledge of basic emissions and fuel systems.
The majority of feedback that has come back regarding the extra information now available using the new scan tools is very good. The technicians have access to data they never used to be able to see, although as mentioned above a lot of training is needed to enable them to correctly interpret this extra data and to understand when the monitors run and do not run.
