History of OBD

1. History of O B D
On Board Diagnostics
1975: Datsun 280Z
largely motivated by their need for real-time tuning of fuel
injection systems
Simple OBD
no standardization in what is monitored or how it is reported

2. 1980

3. Who knows what
A L D L
Stands for ?

4. 1980: General Motors implements a proprietary interface and
protocol for testing of the engine control module (ECM) on the
vehicle assembly line.
The “assembly line diagnostic link”
ALDL

5. the ALDL was not intended for use
outside the factory.
California vehicles for the 1980
the rest of the United States in 1981

6. QuickTime™ and a
Animation decompressor
are needed to see this picture.
 The only available function was "Blinky Codes".
 By connecting pins A and B (with ignition key ON and engine
OFF), the 'Check Engine Light' (CEL) blinks out a two-digit
number that corresponds to a specific error condition.
We didn’t use scanners
we used paper clips

7. 1987 Ford Escort cost $6895
CARB The California Air Resources Board
requires that all new vehicles sold in California
have some basic OBD capability
beginning in
1988
the official of OBD 1

8. Even though OBD 1 is now official
The data link connector and its position are not standardized, nor is
the data protocol.
Each OEM can basically do whatever they want
but they have to turn on the check engine light
to let you know they’ve done something.

9. Each O E M did their own thing
and had their own connector

10. Later in 1988
The Society of Automotive Engineers (SAE)
recommends a standardized diagnostic connector and
set of diagnostic test signals
The OEMS begin ramping up their
OBD 1 functionality

11. 1994
because we needed emission testing
CARB The California Air Resources Board
issues specifications and mandate
that they be adopted for all cars
sold in California beginning in 1996

12. 1996 OBD 1 was made mandatory
for all cars sold in the United States
Mandatory..........
What’s that mean exactly
Every OEM had their own version
and their own trouble codes
and their own diagnostic procedures
They even had their own “Scan Tool”
None of it was “interchangeable”

13. OBD II OBD II
OBD 2 was invented to alleviate OBD 1’s flaws
OBD 2’s main objective is emissions related
 Standardizing all OBD 2 systems – universal fault
codes, data connectors and diagnostic procedures – this
makes it easier for a technician to work on different
makes of cars

14. C A N Controller Area Network
All cars sold in the United States
are required to use CAN

15.  OBD 1 was required to monitor 3 systems:
 EGR systems
 Fuel Metering
 Major sensor inputs – cam, throttle, etc.
 OBD 2 monitors:
 Catalyst efficiency
 Engine misfire
 Enhanced EGR monitor
 Enhanced sensor inputs and outputs
 Enhanced fuel system monitor
 Enhanced heated O2 monitor
 Evaporative emission system integrity
 Secondary AIR system function
 CFC’s in the air conditioning system

16. Terminology
• Diagnostic Monitor – tests by the PCM to
check all OBD systems – failure by any
monitor turns the MIL light on
• Enabling criteria – sensor inputs during specified
driving conditions – must be received by the
PCM before the monitor can be run (engine
temp, speed, load, gear, etc.)
• Warm up cycle – the time it takes the
engine to warm from ambient to 160*F

17. • Active test – a test that forces a monitor to
run or a component to operate – a scan tool
is usually used to run the test
• Failure record – stored DTC memory in the
PCM – stored in order that they occurred,
usually with some freeze data to indicate
conditions – they must be repaired in the order
of 1st to last

18. • Drive cycle – a set of driving conditions that
run all monitors – after all monitors are run,
then the vehicle sets “readiness” for
inspection/maintenance (IM) flags – all tests
have passed when readiness is set
• Passive test – a test that checks the
performance of a vehicle system during
normal operation

19. • Trip – a key on, engine running, key off
cycle in which all the diagnostic criteria
to run a specific monitor is met
• Freeze frame data – serial data values
that are stored the instant a DTC is
set – sped, temp, load, conditions, etc.
• Inspection/maintenance (IM) ready
status – called Readiness – all monitors
have run and passed

20. • Closed loop operation – occurs when the PCM
processes electrical inputs from all sensors to
control the fuel delivery and all systems associated
with the running engine – the engine is getting data
from the sensors, not a base PCM map
• Open loop – vehicle is running and warming
up based on PCM maps – no sensor input is
recognized by the PCM until engine warms
and closed loop occurs

21. OBD trouble codes
• A DTC is displayed as an alphanumeric
designator followed by a 3 digit number
• These codes are displayed on the scanner
• All OBD codes are now standardized, so a
P0411 for a Ford will be the same for a VW,
Chrysler, BMW, etc

22. • Codes fall into 4 groups:
• Body codes : B0, B1, B2, B3
• Chassis codes : C0, C1, C2, C3
• Powertrain codes : P0, P1, P2, P3, P4
• Network codes : U0, U1, U2, U3

23. P codes
• Engine performance DTC’s are found in the
P codes
• If the code is P0xxx – it is a generic,
standardized SAE code – the same code for
all autos
• If the code is a P1xxx – it is a manufacturer
specific code that needs a manufacturer
specific diagnostic procedure – these codes
are not standardized

24. • The second number of a P code, as in P01xx,
designates the affected systems
• 1 – fuel and air metering
• 2 – fuel injectors
• 3 – ignition or misfire systems
• 4 – auxiliary emission controls
• 5 – vehicle speed control and idle
• 6 – computer output circuits
• 7 – transmission
8 – transmission

25. • The last 2 numbers, as in P0137, is the
specific fault
• So, P0137 is a generic engine code, affecting
the fuel metering, and indicates the number
2 heated oxygen sensor on cylinder bank 1
is producing a low voltage
• The number 1 cylinder bank always
contains number 1 cylinder

27. End