Section 5 - Gm Diagnostics; Gm Historic (Obd I) Diagnostics; Manual Info; Read Codes - Actron Professional Enhanced Scan Tool 9640A User Manual

Section 5 – GM Diagnostics
If the Scan Tool displays an Error Message , make sure the cables and
adapters are securely attached and the ignition key is ON. Cycle the igni-
tion key to OFF for 10 seconds, then ON. Attempt the test selected again.
If the problem remains, refer to " Error Messages " on page 8-2.

GM HISTORIC (OBD I) DIAGNOSTICS

Some 1994 and 1995 vehicles use the 16-pin OBD II connector, but are not
OBD II compliant. They still use the OBD I application software. Refer to
" Appendix A - Data Link Connectors ".

Manual Info

The Manual Info function instructs the user what section of the manual to use.
This section covers GM Historic (OBD I) Diagnostics .

Read Codes

The Read Codes function is used to retrieve all stored Diagnostic Trouble
Codes (DTCs) from the control module(s). This can be performed with key ON
engine OFF (KOEO) or key ON engine RUNNING (KOER). Two types of codes
were used by GM in the Historic System: Current codes and History codes.
Prior to 1986, all codes were referred as Current Codes. From 1986 through
1995, both codes were used as the PCM was able to differentiate them.
The tool automatically displays the type of codes that pertain to the vehicle
under test. The DTC types are defined as follows:
• History Codes — intermittent codes placed in the vehicle's memory when
the trouble originally occurred, and will remain there even if the trouble has
been corrected. If no trouble after 50 engine warm-up cycles, the DTC
erases.
• Current Codes — codes transmitted through the PCM's data stream when
a trouble condition is active and cannot be erased. The problem must be
repaired to remove the DTC.
On some vehicles, all codes are Current Codes, because the PCM cannot
distinguish Current Codes from History Codes. The only way to determine
this is to erase the code and then drive the vehicle to see if the code
returns.
Perform the following:
1) Set Parking Brake
2) Turn Key On-Engine Off or Running.
3) Put Transmission In Park Or Neutral.
Select Read Codes from the GM Func-
tion List and press
will retrieve the DTCs.
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