OBD (On Board Diagnostics)
To combat its smog problem in the Los Angela’s basin, the State of California started requir- ing emission control systems on 1966 model cars.The US federal government extended these controls nationwide in 1968. In 1970 the US Congress passed the Clean Air Act and established the Environmental Protection Agency (EPA).The Environmental Protection Agency has been charged with reducing ‘mobile emissions’ from cars and trucks and given the power to require manufacturers to build cars which meet increasingly stiff emissions standards. To meet these standards,manufacturers turned to electronically controlled fuel and ignition systems. Sensors were incorporated to measure engine performance and adjust the systems to provide minimum pollution. These sensors were also accessed to provide early diagnostic information. In 1988, the Society of Automotive Engineers (SAE) set a standard connector plug and a set of diagnostic test signals.The EPA adopted a number of the recommended standards.OBD-II is an expanded set of standards and practices developed by SAE and adopted by the EPA and CARB (California Air Resources Board) which were implemented in 1996.OBD-II provides a universal inspection and diagnosis method to be sure the car is performing to OEM standards.All cars built since 1, January 1996 have OBD-II systems.
EOBD (European On Board Diagnostics)
EOBD is an EU directive and is a part of the Euro Standard Stage 3.This means the compul- sory introduction of a standard system which has the facility to record errors in a vehicle’s engine management system that would affect the output of emissions.
EOBD was introduced on 1 January 2000 for vehicle type approval, which means that only new vehicles conforming to EOBD are licensed in Europe. In simplistic terms, the directive means that all European vehicles manufactured after this date will be fitted with standard 16-pin diagnostic connectors allowing access to emission data. Up to this date manufacturers used a wide range of diagnostic connectors. EOBD is based on the EPA OBD system. The vehicle’s computer must communicate with one of the stated EOBD protocols. In the event of a failure the ‘Malfunction Indicator Light’ (MIL) on the instrument cluster will illuminate to advise the driver that they must take the vehicle to a repair outlet immediately.At the very least, these faults must be rectified before the vehicle will pass an MoT (Ministry of Transport) test.
OBD and EOBD systems were not only designed to reduce pollution being emitted from
vehicles with faults that affect emissions.The systems were also designed to assist in diagnos-
ing any OBD related faults which existed before the vehicle left the assembly line ensuring
that the vehicle conformed to emission standards immediately. OBD also assists in providing
information for the technician on sensor and actuator operation.This often allows technicians
to evaluate system performance, providing valuable diagnostic information. If the system
recognises a fault with a sensor or actuator, then the control module can use ‘failsafe’ measures
to reduce the possibility of producing excessive pollutant from the vehicle. For example, if the
engine coolant temperature sensor failed and provided a signal relating to 0°C for an extended
period then the control module would ignore the signal and use a stored value of 80°C which
would correspondingly reduce the amount of fuel injected into the engine thus reducing pol-
lutants being emitted.The system will operate at a reduced performance but this is often accept-
able enough to allow the vehicle to get back to base.
EOBD and OBD testers
An illuminated or flashing MIL will notify the driver prompting them to take the vehicle to the
workshop for investigation.An EOBD compliant tool will be required to communicate with a
system that complies with EOBD and OBD standards. It is important if working on a range of
manufactured vehicles that your diagnostic tool has the facility to communicate using required
protocols:
SAE protocol – J1850PWM, J1850VPW
ISO protocol – ISO 9141-2, ISO11898, 11519 (CAN) and ISO 14230-4KW2000
Note – in the future (2008) diagnostic testers will communicate with control modules via the
CAN bus (ISO 15765-4).
A car manufacturer can choose any one of these protocols, so make sure that any tools are
fully EOBD/OBD compatible. OBD/EOBD testers will automatically detect which commu-
nication protocol the vehicle uses.Not all EOBD/OBD testers give the same level of informa-
tion. Some will only give a basic code reading facility while others will give access to full data
stream, freeze frame and special test facilities.
Fault codes
The increase in the number of available codes can now give the technician a better under-
standing of where the problem exists.Vehicles with OBD II and EOBD may use up to seven
or eight possible codes relating to an individual sensor or actuator fault. Fault codes must only
be used as information or a guide to prompt further investigation into a system or component.
A check of the associated wiring and components is always required before replacing the sen-
sor or actuator.Remember it is the technician who makes the diagnosis, the machine only pro-
vides them with information and measurements. An appreciation between mechanical and
electronic components must exist.
Fault codes are often referred to as Diagnostic Trouble Codes (DTC) and have been
standardised.This means that all new EOBD and OBD fault codes have a 5 digit alphanumer-
ical code.
A DTC is made up of 5 digits.The information below shows the composition of a DTC code
‘P0100’.
The first digit of the code identifies the system that has the fault, for example:
● B for the body
● C for chassis
● P for powertrain
● U for network communication system
The second digit identifies the standard manufacturer’s code ‘P0100’ or the standard
ISO/SAE code ‘P1100’.
The third digit identifies the diagnostic trouble code group the fault belongs to.
Diagnostic trouble code group
P01. Fuel and air metering
P02. Fuel and air metering
P03. Ignition system or misfire
P04.Auxiliary emission controls
P05.Vehicle speed and idle control system
P06. Computer output circuit, trip computer etc.
P07.Transmission
P08.Transmission
P09. Reserved for ISO/SAE
P00. Reserved for ISO/SAE
The fourth and fifth digits identify the fault, 0–99.
Example codes
Trouble code Fault location
B1343 A/C sunlight sensor – short/open circuit
B1347 A/C foot well vent temperature sensor – short circuit
B1348 A/C foot well vent temperature sensor – short/open circuit
B1352 In-car temperature sensor – short circuit
B1353 In-car temperature sensor – short/open circuit
B1355 A/C/heater blower motor/in-car temperature sensor – supply voltage
B1360 A/C control module – keypad fault
B1493 A/C control module/combination control module/relay – signal fault
B1498 Heated rear window – short circuit
B1515 Common sensor earth – short circuit
B1605 A/C control module – defective
B1675 A/C/heater air direction motor – defective
B1676 A/C/heater recirculation motor – faulty
B1677 A/C/heater air mix flap motor – faulty
B2402 A/C/heater air direction motor – short circuit
B2403 A/C/heater air direction motor – open circuit
B2404 A/C/heater air direction motor – short circuit
B2405 A/C/heater air direction flap – loose
B2406 A/C/heater air direction flap – jammed
B2413 A/C/heater recirculation flap motor – open circuit
B2414 A/C/heater recirculation motor – short circuit
B2426 A/C/heater blower motor – control defective
B2427 A/C/heater blower motor – control defective
B2428 A/C/heater blower motor – control defective
B2492 A/C/heater air mix flap motor – short circuit
B2493 A/C/heater air mix flap motor – open circuit
B2494 A/C/heater air mix flap motor – short circuit
B2495 A/C/heater air mix flap – loose
B2496 A/C/heater air mix flap – jammed
There are two categories of DTC that apply to EOBD and OBD II.
Type A:
1. Emissions related.
2. Requests illumination of the MIL after one failed driving cycle.
3. Stores a freeze frame DTC after one failed driving cycle.
Type B:
1. Emissions related.
2. Sets a pending trouble code after one failed driving cycle.
3. Clears a pending trouble code after one successful driving cycle.
4. Turns on the MIL after two consecutive failed driving cycles.
5. Stores a freeze frame after two consecutive failed driving cycles.
Malfunction Indicator Light (MIL)
The MIL is located in the instrument cluster and takes the form of an engine symbol (inter-
national standard).Whenever the ignition is switched on the system carries out a self-test and
upon successful completion will switch the MIL off. If the MIL does not go out a fault exists
relating to emissions.
Fault detection and storage
A drive cycle begins when the engine is started and ends when the engine is switched off.
During this trip all sensors and actuators are monitored if operated.A readiness trip is when
the engine is started and ends when the monitoring of the systems has completed the tests. This
can occur over a number of drive cycles (due to temperature ranges, distance covered, speed).
A dealer test cycle (dealer drive cycle) is one readiness trip. This means that the vehicle is
driven under a number of conditions (varying load, temperature etc.) to enable the monitor-
ing of all EOBD systems.
MIL signals during these drive cycles are as follows:
1. Occasional flashes show momentary malfunctions. It stays on if the problem is of a more
serious nature, affecting the emissions output or safety of the vehicle.
2. A constantly flashing MIL is a sign of a major problem which can cause serious damage if
the engine is not stopped immediately.
In all cases a ‘freeze frame’ of all sensor readings at the time is recorded in the vehicle’s central
computer.Hard failure signals caused by serious problems will cause the MIL to stay on any time
the car is running until the problem is repaired and the MIL reset. Intermittent failures cause the
MIL to light momentarily and they often go out before the problem is located.The freeze frame
of the car’s condition captured in the computer at the time of the malfunction can be very valu-
able in diagnosing these intermittent problems.However, in some cases if the car completes three
driving cycles without a reoccurrence of the problem, the freeze frame will be erased.
Data link connector (SAE J1962)
The EOBD interface connector allows technicians and traffic monitoring authorities to read
data relating to EOBD and any faults that are present which affect the vehicle’s emission output.
The traffic authorities gain access to the system data using a generic scan tool.This information
figure 3.125
may eventually be used to determine a penalty for a vehicle keeper who is driving a vehicle with
an emission related fault causing the MIL to be illuminated over a prolonged period.
J1962 pin allocation
Pin Definition Purpose
Pin Definition Purpose
1 Ignition control Activation of the low-tension switch (relay etc.) for actuating
the ignition circuit
2 Bus ( ) SCP (J1850) SCP (standard corporate protocol) communication
3 SCL ( )/STAR (out)/ SCL communication (self-test output)/mid-speed CAN
MS-CAN ( ) communication
4 Chassis ground Ground for power supply to data link connector
5 Signal ground Signal return for programming
6 Class C link bus ( ) High speed data transmission bus ( )
7 K cable for ISO 9141 Communications cable for vehicles to ISO 9141
8 Tripping signal Multiple module output
9 Battery power supply Power supply through ignition switch
10 Bus ( ) SCP (J1850) SCP (standard corporate protocol) communication
11 SCL ( )/STAR (in)/ SCL communication (selftest output)/mid-speed CAN
MS-CAN ( ) communication
12 Module programming Programming of flash EEPROM
13 Module programming Programming of flash EEPROM
signal
14 Class C link bus ( ) High speed data transmission bus ( )
15 L cable to ISO 9141 Communications cable for vehicles to ISO 9141
16 B Battery positive power supply to data link connector
The serial link operates at a baud rate (bit rate) of 5–10 Kbaud on a single wire interface or
as a two wire interface with a separate data line using a ‘K’ and ‘L’ line.
Dealer drive cycle (GM)
When a fault code in the memory of a module has been cleared some systems produce a readi-
ness code that is stored in the KAM (Keep Alive Memory).The readiness code P1000 is only
deleted after complete execution of a successful dealer drive cycle.A complete dealer driving
cycle will perform diagnostics on all monitored systems and can usually be completed in less
than 15 minutes.
Preparation – cold start below 50°C and at least 20% in the fuel tank.
Performing a GM OBD II driving cycle:
1. Cold start. In order to be classified as a cold start the engine coolant temperature must be
below 50°C and within 6°C of the ambient air temperature at start-up.Do not leave the key
on prior to the cold start or the heated oxygen sensor diagnostic may not run.
2. Idle.The engine must be run for 21
⁄2 minutes with the air-conditioner and rear defroster on.
The more electrical load you can apply the better.This will test a range of sensor and actu-
ators such as O2 sensor, canister purge,misfire and if closed loop is achieved, fuel trim.
3. Accelerate smoothly. Turn off the air-conditioner and all the other loads and apply half
throttle until 55mph is reached.During this time the misfire, fuel trim, and purge flow diag-
nostics will be performed.
4. Hold steady speed. Hold a steady speed of 55mph for 3 minutes. During this time the O2
response, EGR, purge,misfire, and fuel trim diagnostics will be performed.
5. Decelerate. Let off the accelerator pedal.Do not change gear, touch the brake or clutch. It
is important to let the vehicle coast gradually slowing down to 20mph (32 km/h). During
this time the EGR, purge and fuel trim diagnostics will be performed.
6. Accelerate.Accelerate at
3
⁄4 throttle until 55–60mph.This will perform the same diagnostics
as in step 3.
7. Hold steady speed.Hold a steady speed of 55mph for 5 minutes.During this time, in addi-
tion to the diagnostics performed in step 4, the catalyst monitor diagnostics will be per-
formed. If the catalyst is marginal or the battery has been disconnected, it may take five
complete driving cycles to determine the state of the catalyst.
8. Decelerate.This will perform the same diagnostics as in step 5.Again, don’t press the clutch
or brakes or shift gears.
0 comments :
Post a Comment