Copyright © 1998 General Motors Corp.
6–1
W T E C I I E L E C T RO N I C C O N T RO L S T RO U B L E S H O OT I N G M A N UA L
6–1.
DIAGNOSTIC CODE MEMORY
Diagnostic codes are logged in a list in memory (sometimes referred to as the queue), listing the most recently
occurring code first and logging up to five codes. The codes contained in the list have information recorded as
shown in the chart below (codes are examples). Access to the code list position, main code, subcode and active
indicator is through either the shift selector display or the Pro-Link
®
9000 diagnostic tool. Access to ignition cycle
counter and event counter information is through the diagnostic tool only. Further detail on the use of
Pro-Link
®
9000 is presented in Appendix N of this manual.
The following paragraphs define the different parts of the code list.
A.
Code List Position.
The position which a code occupies in the code list. Positions are displayed as
“d1” through “d5” (Code List Position #1 through Code List Position #5).
B.
Main Code.
The general condition or area of fault detected by the ECU.
C.
Subcode.
The specific area or condition related to the main code in which a fault is detected.
D.
Active Indicator.
Indicates when a diagnostic code is active. The shift selector displays
MODE ON
,
the diagnostic tool displays
YES
.
E.
Ignition Cycle Counter.
Determines when inactive diagnostic codes are automatically cleared from
the code list. The counter is incremented each time a normal ECU powerdown occurs (ignition
turned off). Inactive codes are cleared from the code list after the counter exceeds 25.
F.
Event Counter.
Counts the number of occurrences of a diagnostic code. If a code is already in the
code list and the code is again detected, that code is moved to position d1, the active indicator is
turned on, the Ignition Cycle Counter is cleared, and 1 is added to the Event Counter.
6–2.
CODE READING AND CODE CLEARING
Diagnostic codes can be read and cleared by two methods: by using the Pro-Link
®
9000 diagnostic tool or by using
the shift selector display. The use of the Pro-Link
®
9000 diagnostic tool is described in the instruction manual
furnished with each tool. The method of reading and clearing codes described in this section refers to only entering
the Diagnostic Display Mode by the proper button and/or lever movements on the shift selector.
The Diagnostic Display Mode may be entered for viewing of codes at any speed. Codes can only be cleared when
the output speed = 0 and no output speed sensor failure is active.
A.
Reading Codes.
Enter the diagnostic display mode by pressing the
⇑ (
Up
)
and
⇓ (
Down
)
arrow
buttons at the same time on a pushbutton selector, or by momentarily pressing the
DISPLAY MODE
button on a lever shift selector.
Table 6–1. Code List
Code List
Position
Main Code
Subcode
Active Indicator
Ignition Cycle
Counter
Event Counter
d1
21
12
YES
00
10
d2
41
12
YES
00
04
d3
23
12
NO
08
02
d4
34
12
NO
13
01
d5
56
11
NO
22
02
Displayed on shift selector and diagnostic tool
d = “diagnostic”
YES =
MODE ON
displayed
Not available on shift selector display
S
ECTION
6 — DIAGNOSTIC CODES
