User Manual

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✓ 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".
✓ If an Operating Error message displays, make sure the cables and adapters
are securely attached and the ignition key is ON. Cycle the ignition key to OFF
for 10 seconds, then ON. Attempt the test selected again. If the problem
remains, refer to “Error Messages” on page 7-3.
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 KOEO or 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
Function List and press
(17(5 . The tool
will retrieve the DTCs.
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