Design and Function, On-Board Diagnosis System (OBD)

Diagnostics of A/B Tool
Volvo's microprocessor-based on-board diagnostic system (OBD) can be divided into two functions:

1) Self-diagnosis:
Self-diagnosis enables individual electronic systems in operation to execute function testing and log any faults for later reading and analysis.

2) Test:
The diagnostic test mode (DTM) is a complement to self-diagnosis and acts as an aid during fault tracing and checking of the entire electronic system.

Data Link Connector (DLC)






There are:
cars without data link connector (DLC)
cars with only diagnostic tool A, cable not supplied
cars with diagnostic tool A, cable mounted as an accessory
cars with diagnostic tools A and B.
If the car is equipped with a data link connector (DLC), it is located in the engine compartment.

Manual readings can be performed using the data link connector (DLC)'s LED and push button.


Examples of fault tracing using the data link connector (DLC)





DLC A has an LED and a push button and a selector cable with a contact probe. Using DLC B2, one can perform diagnostics manually using the push button and LED for the cruise control system. Posted DTCs can be retrieved by reading the flashing LED or using a Scan Tool (ST).



Manual reading using the data link connector (DLC)






Place the selector cable contact probe in position 2 on DLC B.
Turn on the ignition.
Select diagnostic test mode (DTM) using the push button.

Data link connector (DLC) is not functioning
If the DLC is not working, fault tracing should be performed, Testing and Inspection Begining Fault tracing.


Manual reading and entering of codes






To activate a diagnostic test mode (DTM), press the push button on data link connector (DLC) A as many times as the number of the desired function, for examples five times for DTM 5.

Thus a DTM is referred to by a three digit code, composed of numbers 0-9. For example 1-4-1. Each digit is represented by as many flashes or pushes of the button, except the digit "0," which is represented by 10 flashes or pushes of the button. The digits are separated by a pause.


Reading






Logged DTCs are read by counting the flashes of the LED. The DTCs are read in the order that they were logged, i.e. first in, first out. A maximum of 7 DTCs can be saved. If the queue becomes full, the most recent code is erased if it has a lower priority than the new DTC.


Manual diagnosis for cruise control system

The cruise control OBD consisting of DTMs 1-2-4-5 is activated using position 2 on data link connector (DLC) B See the following table:

Data link connector (DLC) B2

Diagnostic test mode: Description of diagnostic function:
1: Self diagnosis Reading and erasing logged DTC's
2: Component test Test of included components.
4: Transfer rate Change data transfer rate between control module and DLC.
5: Reason for disengagement Shows most recent reason for cruise control system.

Erase DTCs

The cruise-control system's self diagnosis does not log DTCs (unlike other OBDs) but is instead cleared when ignition is turned off.

Diagnostics With Scan Tool







Scan Tools (ST)
By connecting a Scan Tool:
Volvo Diagnostic Key, one can quickly and easily perform diagnostics and read DTCs.
Performing diagnostics with use of a scan tool below.


Use Of Scan Tools (ST)

Connecting the Scan Tool:
Volvo Diagnostic Key

Note: When connecting to the OBD, the ignition should always be turned off.

See also the Scan Tool manual and Workshop Guide 134, or a later Workshop Guide.
Volvo Diagnostic key, P/N: 988 86570-7
Cabling for Diagnostic key Scan Tool (ST): 951 0040-0

General

Insert a memory cassette in the scan tool. Check to ensure that the correct cassette is used.
Install connector for ST toteminial B.
Attach battery cables to battery, red to positive terminal.
Turn on ignition.
Proceed to: B2
Initiate desired diagnostic test mode.