APPENDIX C 

NEW YORK CITY TAXI & LIMOUSINE 

TRAINING PRESENTATIONS 
Introduction To OBD II Introduction To OBD II

George E. Pataki Raymond P. Martinez Erin M. Crotty

Governor DMV Commissioner DEC Commissioner

Introduction

Onboard Diagnostics, OBD, technology 

benefits motorists, technicians and the 

environment by monitoring a vehicles 

performance every time it is driven, 

identifying performance and emissions 

problems immediately and providing 

technicians with information to help 

them quickly and accurately diagnose 

and repair malfunctions 
Early OBD Systems (Pre – 1996)

 The first OBD systems appeared on vehicles 

in the 1980’s (OBD I) and monitored fuel, 

ignition and emissions systems components. 

 When a fault was found a code was stored in 

the vehicles onboard computer and in many 

instances a “Check Engine” light was lit to 

alert the driver. 

 Technicians could connect to the computer 

and see what codes had been set and make 

a diagnosis of the problem

Early OBD Systems (Pre – 1996)

(Continued)

While the concept was a good one, several practical 

problems were found in actual use.....

 No Standardization of data link connectors – a 

different one needed for each manufacturers vehicles

 Trouble codes not consistent between manufacturers

 No standardization of emissions control device and 

system names between manufacturers

 Criteria to light check engine light not consistent 

between manufacturers

 Type of stored information in vehicles computer 

varied from manufacturer to manufacturer 
OBD II Systems

Noting that OBD systems were valuable technology in 

maintaining good performance and lower emissions in 

vehicles, the U.S. EPA developed regulations that 

required all vehicles meet specific and consistent 

standards for OBD systems, OBD II, by 1996 

These regulations resulted in standardization of,

 Data Link Connector and location in vehicle

 Terminology for vehicle emissions control components

 Diagnostic trouble codes

 Freeze Frame – storage of engine conditions at time a 

DTC is set

 Requirements for lighting MIL (Check Engine Light)

 Determination and recording of readiness status of 

system monitors

DLC

Standardized Data Link Connector

 Allows generic scan tool to be used on all 

OBD II equipped systems.

 Contains 16 terminals – some OBD II 

dedicated and some manufacturer 

discretionary.

 Location of DLC standardized. 
Standardized Terminology

 Different manufacturers used different names 

/ acronyms for essentially the same 

components / systems. 

 The Society of Automotive Engineers, 

S.A.E., developed standardized terminology 

for engine and emissions systems.

 See Glossary in Inspectors Reference Guide

for examples.

OBD Failure Criteria

Reasons for failing an OBD II inspection

MIL does not light with key on – engine off 

(KOEO)

MIL is lit with the key on - engine running 

(KOER)

Scan tool indicates DTC’s, and MIL is 

commanded on by the PCM, even if it is not lit

More than the allowable number of monitors 

are found to be “not ready”

DLC is missing or damaged – communications 

failure
MIL

Malfunction Indicator Light

 The MIL is a light on the dashboard to alert the 

driver of an emissions related problem. The MIL 

will be lit if one of the following conditions is 

present,

 Severe misfire which could cause catalytic converter 

damage will cause it to flash on and off.

 A steadily lit MIL indicates a DTC has been set.

 The OBD II system can turn the MIL off on it’s 

own if it detects that the cause of the MIL being lit 

has been corrected.

DTCs

Diagnostic Trouble Codes

 Prior to OBD II each manufacturer had it’s 

own list of trouble codes. 

 Under OBD II all manufacturers must use a 

universal 5 digit code system. 
DTC’s

Diagnostic Trouble Codes (Continued)

There are two types of DTC’s, 1 trip DTC’s and 2 

trip DTC’s

A 1 trip DTC is for a condition that requires 

immediate attention such as a catalyst damaging 

misfire. 

A 2 Trip DTC is one that a condition must be found 

during 2 consecutive trips such as an EGR fault.

Most Monitors do not set a DTC and light the MIL 

when a vehicle fails a test for the first time during a 

DRIVE CYCLE. If a test is failed on a second 

consecutive DRIVE CYCLE the MIL will light and a 

DTC is stored in the vehicles powertrain control 

module (PCM).

System Monitors 

& Readiness Status

 One of the features of OBD II testing is that the 

vehicle need not be warmed up or preconditioned before doing the test.

 The OBD system periodically runs what are called 

MONITORS to determine if the various emissions 

control devices and systems are READY and able 

to operate as they were designed.

 Some Monitors are CONTINUOUS monitors and 

some are NON-CONTINUOUS monitors.

 Monitors are run during what are called

DRIVE CYCLES
Continuous & Non-Continuous 

Monitors

Some vehicle components are 

continuously tested by OBD II while 

others are only tested under certain 

operating conditions.

Continuous Monitors Continuous Monitors

• Misfire

• Fuel System

• Comprehensive Components

Non-Continuous Monitors Continuous Monitors

• EGR System

• O2 Sensors

• Catalyst

• Evaporative System

• Others (if vehicle equipped) –

Secondary Air, Heated Catalyst,

A/C System

System Monitors 

& Readiness Status

(Continued)

 If a Monitor is run completely and the system / 

component being tested operates properly, the 

monitor is recorded in the powertrain control 

module (PCM) as ready, complete or done. 

 Disconnecting the vehicles battery or clearing 

stored DTCs from the PCM will usually reset the 

monitor readiness status to NOT READY

 1996 – 2000 model year vehicles FAIL if more 

than 2 monitors are “Not Ready”.

 2001 and Newer model year vehicles FAIL if more 

than 1 monitor is “Not Ready”.
Drive Cycles

 What constitutes a DRIVE CYCLE can vary 

from monitor to monitor and across all 

makes and models.

Freeze Frame

 Whenever an emissions related malfunction 

occurs, OBD II stores the operating 

parameters (conditions) present at the time 

the malfunction occurs. 

 Parameters recorded are, but are not limited 

to:

• Fuel Pressure

• Fuel Trim Value ( Rich or Lean )

• Engine Coolant Temperature

• Intake Manifold Pressure

• Open or Closed Loop Status

• This data is valuable to assist technicians in diagnosing the 

cause of the malfunction.

•DTC Description

•Engine Speed

•Vehicle Speed

•Air Flow

•Engine Load
System Reports

The TLC equipment will continue to produce 

reports as in the past.

Rejection Notices for vehicles failing an OBD II 

inspection will contain the following added 

information,

 Status of communication with PCM

 Listing of DTC’s found stored

 Number of monitors found “Not Ready”

 MIL status check 
Ford Crown Victoria Ford Crown Victoria 

&

OBD/IM Readiness OBD/IM Readiness
Contents Contents

 Introduction To OBD Review Of OBD Monitors P1000 Code & IM Readiness OBD Emission Inspection OBD Resources
What Is OBD? What Is OBD?

 Real-time, on-board monitoring system that is 

embedded in the Powertrain Control Module (

 Monitors all emission related components and 

systems as mandated by government agencieEPA and CARB.

 Fault is communicated to the customer by me

the “Check Engine” light, also known as the Malfunction Indicator Light (MIL), along with Diagnostic Trouble Code (DTC) set in the PCM
Brief History Of OBD Brief History Of OBD

 OBD-I was implemented 

for 1988 and later model year vehicles.

 Monitoring limited to –

 Oxygen Sensor EGR System Fuel System Input Components

 MIL illuminated only 

while the fault is present.

 OBD-II was implemen

all vehicle lines in 199year vehicles.

 Monitoring extended t

 Oxygen Sensor (enhan EGR System (enhanced Fuel System (enhanced Input/Output Compone Catalyst Efficiency Misfire Evaporative System Secondary Air System

 MIL is illuminated and 

until there are 3 consewithout the fault being 
OBD Monitors OBD Monitors

MisfireExhaust Gas Re-circulation (EGR)EVAPHeated Exhaust Gas Oxygen Sensor (HECatalyst EfficiencyFuelSecondary AirComprehensive Component Monitoring 
What Turns On The MIL? What Turns On The MIL?

Front HEGORear HEGOHEGO HeatersProcessorWiring harness

HEGO

Vacuum linesFuel InjectionAir inlet systemFuel pumpThermostatPositive CrankVentIntake ManifoldThrottle BodyExhaust ManifoldExhaust PipesExhaust Mufflers-ResonatorsFuel LinesMass AirFlow SensorWiring harnessIdle Air ControlProcessorFuel pressure reg.

Fuel

Base engineProcessorFuel InjectorSpark PlugSpark PlugWireIgnition CoilIgnition CoilWireEDISCrank PositionSensorCrank PositionWheelDamperIgnition DiagnosticMonitorFuel Pressure RegulatorWiring harnessOil qualityFuel Quality

Misfire

EGR ValveEGR HosesElectronic VacuumRegulationDelta PressureFeedback Sens.EGR Valve Pos.SensorWiring harnessEGR TubeManuf. or exhaustgas debrisVacuum linesReservoirEGR

Air PumpAir Control ValveVacuum SolenoidWiring harnessVacuum lines

Sec. Air

CatalystFront HEGORear HEGOProcessor PinsWiring harness

Catalyst

Vapor MgmntValveCanister VentSolenoidGas CapVapor CanisterFuel Tank Press.TransducerVapor HosesWiring harnessVacuum linesFuel pump

Evap

Distribution Relays, battelectricalVacuum linIgnition CoiWiring harnFuel Temp.Flex Fuel STransmissioRange SensShift SolenoTurbine ShaSpeed SensElectronic PSolenoidOutput ShaSpeed SensAir ChargeTemp.Cooling FanThermostatKnock SensIntake ManiCommunicaControl

MIL ON
Fault Filtering Fault Filtering

 Typically, circuit fault have to be present for 

consecutive seconds before a DTC is stored.

 DTC is stored if fault is detected. MIL is illuminated only if fault is present for 2 

consecutive drive cycles.

 The MIL is turned off after 3 consecutive trips 

without the fault being present.

 The DTC is erased from memory after 40 war

without the fault being present.
P1000 Code & IM Readiness P1000 Code & IM Readiness

 "P1000" code. Don’t look at a P1000 code as a fault code. "P1000" code. Don’t look at a P1000 code as a fault code. I/M pr

a set of I/M Readiness flags that tell which OBD monitors a vehicle has, abeen run since codes were last cleared (or battery disconnected).

 EPA's OBD Technical Guidance, applicable to testing of 1996 and later Mo

duty vehicles (< 8500 lbs. GVWR) allows:

9 no more than two unset readiness monitors for 1996 through 2000 M

vehicles

9 and no more than one unset readiness monitor for 2001 and newer M

vehicles. 

9 Note that the Guidance is not applicable to vehicles which exceed 850

States are, however, allowed to conduct such testing, but readiness ceither rejection from testing or pass/fail determination may vary amo

 Not all monitors need to be run in order to get through an I/M te

eliminate the P1000, it means all monitors have been run, even though threquirement could have allowed up to two monitors to be not ready. 

*To run all the monitors when it is not necessary, is a waste of ti

resources.
How Do I Pass The OBDII Emission Ins

How Do I Pass The OBDII Emission Ins

 Essentially, five things must be satisfied to pass the inspection:

1. The emissions MIL must illuminate with the key on and eng2. The emissions MIL must be commanded off by the OBD II sy3. Required readiness monitors must be completed.4. No MIL with the key on engine running (KOER)5. Must have communication 

*You can easily verify that you will pass the 1st criteria by confirming that the 

up when the key is turned to the engine on position (but not started). You cathe engine and see if the MIL stays on. If it is on, you will fail the 2nd criteria

vehicle must be repaired before you can pass the test.
My Taxi Didn’t Pass My Taxi Didn’t Pass

Now What Do I do? It depends on why it didn’t pass.

 If the emissions MIL is on, the OBD II system has fou

problem that needs to be fixed. 

 If the MIL won’t light, then the bulb and/or circuitry 

repaired. 

 If the required readiness monitors are not set, then a

driving is required.

* There are many reasons the monitors could be set to “not ready

this is caused by routine maintenance. For instance, if the battedisconnected for any reason, the monitors of most vehicle are rservice technician may have to reset them as part of a repair pr

* Essentially, the car must be driven to reset the monitors. See ha

“Drive Cycle Recommendations”.
OBD Resources OBD Resources

California Air Regulatory Board (CARB) 

web site –

arbis.arb.ca.gov/msprog/obdprog/obdpro

Environmental Protection Agency web s

www.epa.gov/OMSWWW/obd.htm
OBD Resources OBD Resources

www.motorcraft motorcraft.com