Features and technology of
5.4.4 Features and technology of
the catalytic converter with respect to emis- sions of HC only.
current systems
● The presence of engine misfires in the engine To avoid false detection, the legislation allows operation region within the following bound-
verification and healing strategies. These are out- ary conditions.
lined as follows.
● Oxygen sensor deterioration. ● Other emission control system components or
MIL activation logic for detected
systems, or emission-related powertrain com-
malfunctions
ponents or systems which are connected to a computer, the failure of which may result in
To avoid wrong detections the legislation allows tailpipe emission exceeding the specified limits.
verification of the detected failure. The failure is ● Any other emission-related powertrain com-
stored in the fault memory as a pending code ponent connected to a computer must be moni-
immediately after the first recognition but the tored for circuit continuity.
MIL is not activated. The MIL will be illuminated ● The electronic evaporative emission purge
in the third driving cycle, in which the failure has control must, at a minimum, be monitored for
been detected; the failure is then recognised as a circuit continuity.
confirmed fault.
On-board diagnostics 79
Speed (km/h)
Part Two 120
Part One
80 Elementary urban cycle
0 Time(s) 195
Figure 5.20 New European driving cycle (NEDC)
MIL healing
● closed or open loop operation (if available); The MIL may be de-activated after three subse- ● the fault code which caused the data to be
quent sequential driving cycles during which the
stored.
monitoring system responsible for activating the MIL ceases to detect the malfunction and if no
5.4.5 OBD cycles
other malfunction has been identified that would independently activate the MIL.
Directive 98/69/EC defines three different types of driving cycle:
Healing of the fault memory
1. Type 1 test (the NEDC, (Figure 5.20)) defined The OBD system may erase a fault code, dis-
in Annex III, Appendix 1 of the directive; tance travelled and freeze-frame information if
2. A ‘driving cycle consists of engine start-up, a the same fault is not re-registered in at least forty
driving mode where a malfunction would be engine warm-up cycles.
detected if present, and engine shut off;
3. A ‘warm-up cycle’ means sufficient vehicle
Freeze frame
operation such that the coolant temperature This is a feature that can assist in the diagnosis of
has risen by at least 22°C from engine starting intermittent faults. Upon determination of the
and reaches a minimum temperature of 70°C. first malfunction of any component or system, ‘freeze frame’ engine conditions present at the time must be stored in the computer memory.
5.4.6 Monitors and readiness
Stored engine conditions must include, but are
flags
not limited to: An important part of the OBD system is the system
● calculated/derived load value; monitors and associated readiness flags (Figure ● engine speed;
5.21). These readiness flags indicate when a mon- ● fuel trim values (if available);
itor is active. Certain monitors are continuous, for ● fuel pressure (if available);
example, misfire and fuel system monitors. ● vehicle speed (if available);
Monitor status (Ready/Not Ready) indicates ● coolant temperature;
if a monitor has completed its self evaluation ● intake manifold pressure (if available);
sequence. System monitors are set to ‘Not Ready’
80 Advanced automotive fault diagnosis
Figure 5.22 Sixteen Pin DLC OBD2/EOBD connector
occur with the engine electronic control system; particularly faults that could affect the emission control system and this is one of its primary functions. For the diagnostic technician this is a powerful feature which can clearly assist in locating and rectifying problems on the vehicle when they occur.
The diagnostic socket used by systems con- forming to EOBD/OBD2 standards (Figure 5.22) should have the following pin configuration:
Figure 5.21 System monitors (marked as ‘Complete’) and live data shown in scan tool
1. Ignition positive supply
2. Bus ⫹ Line, SAE J1850 (PWM)
3. Manufacturer’s discretion if cleared by scan tool and/or the battery is discon-
4. Chassis ground
nected. Some of the monitors must test their com-
5. Signal ground
ponents under specific, appropriate preconditions.
6. CAN bus H
● The evaporative system monitor has tempera-
7. K Line
8. Manufacturer’s discretion ● The misfire monitor may ignore input on
ture and fuel fill level constraints.
9. Manufacturer’s discretion rough road surfaces to prevent false triggers.
10. Bus – Line (PWM)
● The oxygen sensor heater must monitor from
11. Manufacturer’s discretion
a cold start.
12. Manufacturer’s discretion
13. Manufacturer’s discretion Most other system monitors are not continuous
14. CAN bus L
and are only active under certain conditions. If
15. L line or second K line these conditions are not fulfilled then the readi-
16. Vehicle battery positive. ness flag for that monitor is set to ‘not ready’.
Until the readiness flags are set appropriately. It With the introduction of OBD2 and EOBD this is not possible to perform a test of the OBD sys-
feature was made even more powerful by making tem and its associated components.
it more accessible. Standardisation of the interface There is no universal drive cycle that is guaran-
connector known as the diagnostic link connector teed to set all the system monitors appropriately for
(DLC) and communication protocol allowed the
a test of the OBD system. Most manufacturers and development of generic scan tools, which could be even cars have their own specific requirements and
used on any OBD compliant vehicle. irrespective of this, there are still some specific
Most systems in use involve two types of codes. vehicles that have known issues when trying to set
The generic codes associated with the OBD stand- readiness flag status. As mentioned above, some
ard and manufacturer specific codes. The generic allowance has been made for vehicles of model
codes have a specific structure that allows easy year 1996 to 2000 which can show two readiness
identification and are common across all manufac- flags to be ‘not ready’. After this, 2001 onwards,
turers (Figure 5.23). That is, a certain fault code one readiness flag is allowed to be ‘not ready’ prior
means the same thing on any vehicle, irrespective to a test.
of the manufacturer (Figure 5.24). All basic scan tools are capable of reading these generic codes.