Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 147

DIAGNOSIS - OBD-I[ (On-Board Diagnostic System )
FO
REFERENC E
BD-
If
(On-Board Diagnostic system )
OBD regulations refer to those regulations used in the U .S .A .
In order to detect if the vehicle is emitting harmful exhaust gases into the atmosphere, the OBD system
enables the Engine ECU *' to detect any malfunctions of the engine and exhaust control systems and
warn the driver of such conditions via the "CHECK ENGINE" lamp * z .
There are two types of OBD regulations, namely OBD- I and OBD-I[ . OBD- I regulations are satisfied
with the diagnostic system that has been conventionally used by Toyota . OBD-II regulations require the
functions shown in the table below against OBD- I regulations .
* i
*z
SAE term ; ECM ( engine control module)
SAE term ; MIL (malfunction indicator lamp)
0= Required .
x =
Not require d
Required item
OBD- I
OBD-II
• Detect malfunctions and turn on "CHECK ENGINE" lamp
0
( 8 items)
0
(41 items )
• Standardize malfunction codes x
0
• Output Engine ECU data
x
0
(17 items )
• Freeze-frame data*
x
0
(13 items )
• Communicate between Engine ECU and diagnostic tool x
0
• Standardize diagnostic tools
x
0
• Standardize diagnostic connectors x
0
*An Engine ECU function to store important control data into internal memory during the detection of a
malfunction .
The main characteristic of OBD-II is the unifica-
tion of diagnostic codes and the use of a
special-purpose tester . As a result, communica-
tion protocol between the tester and the DLC
(Date Link Connector) and Engine ECU are stan-
dardized . Furthermore, in the case of OBD-II,
measurement of engine rpm and inspection of
each function of the Engine ECU cannot be per-
formed without using a special-purpose tester .
Toyota employs a system in which original
functions have been added to those required by
OBD-II regulations . The following describes
some of the major differences between
Toyota's conventional OBD system and the
new OBD system (OBD-II) provided in vehicles
sold in the U .S .A . and Canada .