History of O B DOn 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

1980

Who knows what

A L D L

Stands for ?

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”

A L D L

the ALDL was not intended for use outside the factory.

California vehicles for the 1980

the rest of the United States in 1981

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.

QuickTime™ and aAnimation decompressor

are needed to see this picture.

We didn’t use scannerswe used paper clips

1987 Ford Escort cost $6895

The California Air Resources BoardCARB

requires that all new vehicles sold in California

have some basic OBD capability

1988beginning in

the official of OBD 1

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 lightto let you know they’ve done something.

Each O E M did their own thing and had their own

connector

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

1994because we needed emission testing

CARB The California Air Resources Board

issues specifications and mandatethat they be adopted for all cars

sold in California beginning in 1996

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”

1996 OBD 1 was made mandatoryfor all cars sold in the United States

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

C A N Controller Area Network

All cars sold in the United States

are required to use CAN

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

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

•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

•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

•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

•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

•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

OBD trouble codes

•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

•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

P codes

• 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

•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

End