obd ii diagnostic trouble codes

OBD-II Diagnostic Trouble Codes

What is OBD-II?

On-Board Diagnostic systems are in most cars and light trucks on the

road today. During the '70s and early 1980's manufacturers started

using electronic means to control engine functions and diagnose engine

problems. This was primarily to meet EPA emission standards. Through

the years on-board diagnostic systems have become more sophisticated.

OBD-II, a new standard introduced in the mid-'90s, provides almost

complete engine control and also monitors parts of the chassis, body

and accessory devices, as well as the diagnostic control network of

the car.

Why do we need it?

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. The manufacturers must further maintain the emission

standards of the cars for the useful life of the vehicle. OBD-II

provides a universal inspection and diagnosis method to be sure the

car is performing to OEM standards. While there is argument as to the

exact standards and methodology employed, the fact is there is a need

to reduce vehicle emitted pollution levels in our cities, and we have

to live with these requirements.

Does my car have OBD-II?

All cars built since January 1, 1996 have OBD-II systems.

Manufacturers started incorporating OBD-II in various models as early

as 1994. Some early OBD-II cars were not 100% compliant. to see the

dates OBD-II started being included on specific makes and models.

There are three basic OBD-II protocols in use, each with minor

variations on the communication pattern between the on-board

diagnostic computer and the scanner console or tool. While there have

been some manufacturer changes between protocols in the past few

years, as a rule of thumb, Chrysler products and all European and most

Asian imports use ISO 9141 circuitry. GM cars and light trucks use SAE

J1850 VPW (Variable Pulse Width Modulation), and Fords use SAE J1850

PWM (Pulse Width Modulation) communication patterns. to see which cars

use each system.

You may also tell which protocol is used on a specific automobile by

examining the connector socket carefully. If the dash connector has a

pin in the #7 position and no pin at #2 or #10, then the car has the

ISO 9141 protocol. If no pin is present in the #7 position, the car

uses an SAE protocol. If there are pins in positions #7 and #2 and/or

#10, the car may use the ISO protocol.

While there are three OBD-II electrical connection protocols, the

command set is fixed according to the SAE J1979 standard.

Tell me about that "Check Engine Light".

The service industry calls the Check Engine light on your dash an

"MIL" or Malfunction Indicator Light. It shows three different types

of signals. 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. 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 central computer of the

vehicle.

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 valuable in diagnosing these

intermittent problems. However, in some cases if the car completes

three driving cycles without a re-occurrence of the problem, the

freeze frame will be erased.

OBD-II and your car's health

Because of their investment in the equipment required, most repair

shops charge a fee, some-times substantial, to attach the scanning

equipment and diagnose problems using the OBD-II system signals. Home

mechanics and small shop technicians have been restricted from working

with these signals by the cost and technical complexity of the

equipment. With the introduction of more economical and user friendly

scanning devices, it is now practical for almost anyone to access

OBD-II signals and use them for their own testing and repairs.

Scanners vary greatly in their complexity. The best connect easily and

use software to quickly and automatically call up the OBD-II

information. They should have recording ability so that data can be

collected during a test drive without distracting the technician

driving the car. A system connecting to a laptop or desk top computer

provides expanded memory for data and the ability to export data to a

spreadsheet or graphing utility.

Proprietary Sensor Readings

Though not part of the EPA's OBD II standard, the diagnostic read-outs

used by dealership technicians are also read through the OBD II

connector. These service codes show you such things as knock sensor

operation, FI pulse width, ignition voltage, individual cylinder

misfires, transmission shift points and ABS brake condition. There can

be over 300 readings available, depending on the vehicle manufacturer

and model. Vehicles vary in the readings they will support. Scanners

vary widely in the number of these signals that they can read. Some

show just the basic OBD or OBD II signals, others show the full range

of service codes.

OBD-II and performance tuning

While the vast number of drivers want nothing more than dependable,

economical transportation, many of us are looking to OBD-II for extra

performance. Earlier on-board computer systems had chips that could be

replaced to adjust engine parameters for extra speed and power. While

the OBD-II systems are sealed and do not allow chip replacement, they

do provide a real time data acquisition system that is useful to

tuners.

Power loaders can actually reprogram the performance parameters of the

OBD-II system to accommodate performance options. At the current time

the number of models they can service is limited, but the range is

being extended. Be sure the person doing your reprogramming keeps the

car in compliance with EPA emission standards. As aftermarket

manufacturers develop additional solutions, we will add their

information to our links.

For information on the AutoTap PC and PDA-based OBDII scan tool, visit

www.autotap.com.

OBD-II Diagnostic Trouble Codes

*

* P0100- P0199

* P0300-P0399

* P0500-P0599

* P0700-P0799

* P0900-P0999

* P01100-P1199

* P1300-P1399

* P1500-P1599

* P1700-P1799

* P1900-P1999

* P0200-P0299

* P0400-P0499

* P0600-P0699

* P0800-P0899

* P100-P1099

* P1200-P1299

* P1400-P1499

* P1600-P1699

* P1800-P1899

Source: Auto Repair