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Old 19-06-2010, 03:41 PM
Gibbmodoll Gibbmodoll is offline
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Join Date: Oct 2009
Location: Madley in Herefordshire Uk.
Posts: 458
Thumbs up About EOBD.

ON BOARD DIAGNOSTICS

What do I need
Scantool software.
INTRODUCTION

On Board Diagnostics and our European On Board Diagnostics (formerly called OBDII) originated in the USA as this quote from their Environmental protection Agency shows.
"On-Board Diagnostics, or "OBD," is a computer-based system built into all 1996 and later light-duty vehicles and trucks, as required by the Clean Air Act Amendments of 1990. OBD systems are designed to monitor the performance of some of an engine's major components including those responsible for controlling emissions"
OBD is accessed via a 16pin connector - the DLC (Data Link Connector) aka diagnostic socket.
This has to be sited close to the drivers footwell, so sometimes it is behind a lift up flap low down on the dash, or in the case of the 45, it is at the front of the centre console on the drivers side near the clutch pedal.
All petrol vehicles sold in the USA from 1996 had to have this socket and fully implemented OBD. This means those never destined for the USA may be, may partially be, or may not be compliant at all. In Europe petrol vehicles from 2001 and diesel vehicles from 2004 had to be compliant.
Please note, pin 16 is permanently at battery volts and only a few of the positions will be fitted with a contact.
Faults which affect the emissions result in a fault code - a DTC (diagnostic trouble code) being logged by the ecu, which can then be read out to determine the problem and possible cause.
Serious faults also turn on the check engine light/engine warning light, more correctly known as the MIL (Malfunction Indicator Light) to indicate that you should take the vehicle to a dealer for attention.
Very serious faults affecting safety or resulting in engine damage can also cause a reduction in power - so called limp home modes. These vary from just a moderate lack of power & reduced rev limit to almost complete power loss - with just enough to crawl home or to a garage at 30mph.


What can I use it for?
A) Listing and clearing DTCs & resetting the MIL.
You can identify the DTC & what has caused it, clear it & reset the MIL if your vehicle is fully EOBD compatible.
On fully compliant cars, you can also examine the 'freeze frame' data.This is a snapshot of the sensor data at the instant the DTC was logged by the ecu.
This is a list of modes which should be supported. Often not all are, even though the software can appear to support all of them.
In other words, just because the software reports no DTCs, doesn't mean there aren't any. Only if your vehicle is reported as being OBD COMPLIANT, should you believe exactly what you see!.
01 SHOW CURRENT DATA including OBD compatibility
02 SHOW FREEZE FRAME DATA - sensor data at the time a DTC was logged.
03 SHOW STORED TROUBLE CODES
04 CLEAR TROUBLE CODES AND STORED VALUES - also may reset learned values.
05 SHOW TEST RESULTS - OXYGEN SENSORS - CONTINUOUSLY MONITORED
06 SHOW TEST RESULTS - NON CONTINUOUSLY MONITORED
07 SHOW PENDING TROUBLE CODES - faults that have been detected but have not recurred enough times to be a 'current' DTC.
08 SPECIAL CONTROL MODE - often used to activate idle steppers, egr valves etc.
09 REQUEST VEHICLE INFO - eg VIN etc
B) Displaying & logging sensor data. I can select from some or all of the following & view & log the data whilst driving.
AIR INTAKE TEMP
COOLANT TEMP
MASS AIR FLOW To convert gm/sec into kg/hr, multiply by 3.6
BOOST PRESSURE To convert Kpa absolute to psi relative, multiply by 0.145 and subtract 14.5.
RPM Shows my tacho to be about 150rpm high at 2500rpm
VEHICLE SPEED - speedo also reads high though the true speed depends upon the tyre rolling radius being factory specd.
INJECTION TIMING ADVANCE
CALCULATED LOAD VALUE not as much use as you might think.
THROTTLE POSITION handy to be able to see that you are getting full throttle.

__________________
All the best Gibbmodoll.
(Gibbins Motors Technology and Gibbmodoll Uk Group).
The more you know, the less you know.
Here is one more great site run by the Group,

http://www.uklovedollforums.co.uk/home.php
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