The California Air Resources Board (CARB) began regulation of
On Board Diagnostics (OBD) for vehicles sold in California beginning
with the 1988 model year. The first phase, OBD-I, required monitoring of
the fuel metering system, Exhaust Gas Recirculation (EGR) system and
additional emission related components. The Malfunction Indicator Lamp
(MIL) was required to light and alert the driver of the fault and the
need for repair of the emission control system. Associated with the MIL
was a fault code or Diagnostic Trouble Code (DTC) idenfying the specific
area of the fault.
The OBD system was proposed by CARB to improve air quality by
identifying vehicle exceeding emission standards. Passage of the
Federal Clean Air Act Amendments in 1990 has also prompted the
Environmental Protection Agency (EPA) to develop On Board Diagnostic
requirements. CARB OBD-II regulations were followed until 1999 when the
federal regulations were used.
The OBD-II system meets government regulations by monitoring
the emission control system. When a system or component exceeds emission
threshold or a component operates outside tolerance, a DTC will be
stored and the MIL illuminated.
The diagnostic executive is a computer program in the Engine
Control Module (ECM) or PowertrainControl Module (PCM) that coordinates
the OBD-II self-monitoring system. This program controls all the
monitors and interactions, DTC and MIL operation, freeze frame data and
scan tool interface.
Freeze frame data describes stored engine conditions, such as
state of the engine, state of fuel control, spark, RPM, load and warm
status at the point the first fault is detected. Previously stored
conditions will be replaced only if a fuel or misfire fault is detected.
This data is accessible with the scan tool to assist in repairing the
vehicle.
The center of the OBD-II system is a microprocessor called the Engine Control Module (ECM) or Powertrain Control Module(PCM).
The ECM or PCM receives input from sensors and other
electronic components (switches, relays, and others) based on
information received and programmed into its memory (keep alive random
access memory, and others), the ECM or PCM generates output signals to
control various relays, solenoids and actuators.
2. Configuration of hardware and related terms
1) GST (Generic scan tool)
2) MIL (Malfunction indication lamp) - MIL activity by transistor
The Malfunction Indicator Lamp (MIL) is connected between ECM
or PCM-terminal Malfunction Indicator Lamp and battery supply (open
collector amplifier).
In most cars, the MIL will be installed in the instrument panel. The lamp amplifier can not be damaged by a short circuit.
Lamps with a power dissipation much greater than total
dissipation of the MIL and lamp in the tester may cause a fault
indication.
? At ignition ON and engine revolution (RPM)< MIN. RPM, the MIL is switched ON for an optical check by the driver.
3) MIL illumination
When the ECM or PCM detects a malfunction related emission
during the first driving cycle, the DTC and engine data are stored in
the freeze frame memory. The MIL is illuminated only when the ECM or PCM
detects the same malfunction related to the DTC in two consecutive
driving cycles.
4) MIL elimination
•
Misfire and Fuel System Malfunctions:
For misfire or fuel system malfunctions, the MIL may be
eliminated if the same fault does not reoccur during monitoring in three
subsequent sequential driving cycles in which conditions are similar to
those under which the malfunction was first detected.
•
All Other Malfunctions:
For all other faults, the MIL may be extinguished after three
subsequent sequential driving cycles during which the monitoring system
responsible for illuminating the MIL functions without detecting the
malfunction and if no other malfunction has been identified that would
independently illuminate the MIL according to the requirements outlined
above.
5) Erasing a fault code
The diagnostic system may erase a fault code if the same
fault is not re-registered in at least 40 engine warm-up cycles, and the
MIL is not illuminated for that fault code.
6) Communication Line (CAN)
•
Bus Topology : Line (bus) structure
•
Wiring : Twisted pair wire
•
Off Board DLC Cable Length : Max. 5m
•
Data Transfer Rate
–
Diagnostic : 500 kbps
–
Service Mode (Upgrade, Writing VIN) : 500 or 1Mbps)
7) Driving cycle
A driving cycle consists of engine start up, and engine shut off.
8) Warm-up cycle
A warm-up cycle means sufficient vehicle operation such that
the engine coolant temperature has risen by at least 40 degrees
Fahrenheit from engine starting and reaches a minimum temperature of at
least 160 degrees Fahrenheit.
9) DTC format
•
Diagnostic Trouble Code (SAE J2012)
•
DTCs used in OBD-II vehicles will begin with a letter and are followed by four numbers.
The letter of the beginning of the DTC identifies the
function of the monitored device that has failed. A "P" indicates a
powertrain device, "C" indicates a chassis device. "B" is for body
device and "U" indicates a network or data link code. The first number
indicates if the code is generic (common to all manufacturers) or if it
is manufacturer specific. A "0" & "2" indicates generic, "1"
indicates manufacturer-specific. The second number indicates the system
that is affected with a number between 1 and 7.
The following is a list showing what numbers are assigned to each system.
•
1 : Fuel and air metering
•
2 : Fuel and air metering(injector circuit malfunction only)
•
3 : Ignition system or misfire
•
4 : Auxiliary emission controls
•
5 : Vehicle speed controls and idle control system
•
6 : Computer output circuits
•
7 : Transmission
The last two numbers of the DTC indicates the component or section of the system where the fault is located.
10) Freeze frame data
When a freeze frame event is triggered by an emission related
DTC, the ECM or PCM stores various vehicle information as it existed
the moment the fault ocurred. The DTC number along with the engine data
can be useful in aiding a technician in locating the cause of the fault.
Once the data from the 1st driving cycle DTC ocurrence is stored in the
freeze frame memory, it will remain there even when the fault ocurrs
again (2nd driving cycle) and the MIL is illuminated.
•
Freeze Frame List
a.
Calculated Load Value
b.
Engine RPM
c.
Fuel Trim
d.
Fuel Pressure (if available)
e.
Vehicle Speed (if available)
f.
Coolant Temperature
g.
Intake Manifold Pressure (if available)
h.
Closed-or Open-loop operation
i.
Fault code
3. OBD-II Readiness Test
[Kia Motors Drive Cycle]
Kia OBDII Drive Cycle is designed to execute and complete the
OBDII monitors. To complete a specific monitor for repair verification,
follow the Drive Cycle chart below.
Kia OBDII Drive Cycle consists of two modes (Mode 1 and Mode
2) and the Mode 2 is to perform the catalyst diagnostics on Dephi EMS
only.
–
Continental, Bosch or Kefico EMS : Mode 1 drive cycle should be done one time for diagnostics on all systems.
–
Dephi EMS : Mode 2 drive cycle should be done two times in a
row after Mode 1 is carried out one time for diagnostics on all systems
Smooth cornering
Avoid braking or gear changing in corners, especially when roads are wet. Ideally,
corners should always be taken under gentle acceleration. If you follow these suggestions,
tire wear will be he ...