of the 5-way connector. If continuity is not present,
repair circuit for an open. If present, continue to step
4.
(4) Install 5-way connector back into the mode
door actuator. Then check for continuity between
pins #7 and #16 of the 21-way connector. If continu-
ity is present, replace the ATC control. If continuity
is not present, replace the mode door actuator.
DIAGNOSTIC TROUBLE CODE 19—MODE
DOOR FEEDBACK SHORTED TO GROUND
(1) Remove the 21-way connector from the control,
and the 5 way connector from the mode door actua-
tor.
(2) Check for continuity between pin #16 of the
21-way connector and chassis ground. If present, re-
pair circuit for short to ground. If not present, con-
tinue to step 3.
(3) Plug in the 5-way connector and measure resis-
tance between pins #7 and #16 of the 21-way con-
nector. If the resistance is less than 10 ohms, replace
the actuator. If not, replace the control head.
DIAGNOSTIC TROUBLE CODE 20—BLEND
DOOR MOVED DURING MODE DOOR TEST
(1) Remove the 21-way connector from the control
and the 5-way connector from the three actuators.
(2) Check for continuity between pin #4 of the 21-
way connector and pin #4 of each actuator. If conti-
nuity is not present for a particular actuator circuit,
repair that circuit and retest system. If continuity is
present for all circuits, continue to step 3.
(3) Plug in the 5-way connectors and check for re-
sistance between pins #4 and #6 of the 21-way con-
nector for the blend air actuator. Then check pins #4
and #5 of the 21-way connector for the mode actua-
tor. The resistance should be between 20-50 ohms. If
either of the actuators do not pass the resistance
tests, replace that particular actuator and retest the
system. If both pass the resistance test, replace the
ATC control.
DIAGNOSTIC TROUBLE CODE 21—ROM
CHECK SUM ERROR
During the Diagnostics test, the computer will ver-
ify it’s own internal program. If it finds any part to
be bad, a Diagnostic Trouble Code 21 will be set.
This Diagnostic Trouble Code is not serviceable. If a
Fail Code 21 occurs, the ATC Control Module must
be replaced.
DIAGNOSTIC TROUBLE CODE 22—COMPUTER
ERROR
If incorrect data is found in the ATC Control com-
puter module, a Diagnostic Trouble Code 22 will be
set. This Fail Code is not serviceable. If a Diagnostic
Trouble Code 22 occurs, the ATC Control Module
must be replaced.
DIAGNOSTIC TROUBLE CODE 23—BLEND
DOOR FEEDBACK FAILED
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
back failure immediately upon power up, but the Di-
agnostic Trouble Code will not be set until the time
limit has been met.
Diagnostic Trouble Code 23 will be stored within
the ATC Control, and must be cleared after the fail-
ure has been repaired. To clear this Diagnostic Trou-
ble Code, refer to Erasing Diagnostic Trouble Codes
23 through 28 from ATC Control.
Follow service procedures for Diagnostic Trouble
Codes 14 and 15 when repairing.
DIAGNOSTIC TROUBLE CODE 24—MODE
DOOR FEEDBACK FAILED
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
back failure immediately upon power up, but the Di-
agnostic Trouble Code will not be set until the time
limit has been met.
Diagnostic Trouble Code 24 will be stored within
the ATC Control, and must be cleared after the fail-
ure has been repaired. To clear this Diagnostic Trou-
ble Code, refer to Erasing Diagnostic Trouble Codes
23 through 28 From ATC Control.
Follow service procedures for Diagnostic Trouble
Codes 18 and 19 when repairing.
DIAGNOSTIC TROUBLE CODE 25—AMBIENT
TEMPERATURE SENSOR FAILURE
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
back failure immediately upon power up, but the Di-
agnostic Trouble Code will not be set until the time
limit has been met.
Diagnostic Trouble Code 25 will be stored within
the ATC Control, and must be cleared after the fail-
ure has been repaired. To clear this Diagnostic Trou-
ble Code, refer to Erasing Diagnostic Trouble Codes
23 through 28 from ATC Control.
Follow service procedures for Diagnostic Trouble
Code 11 when repairing.
DIAGNOSTIC TROUBLE CODE 26—IN-CAR
TEMPERATURE SENSOR/ASPIRATOR FAILED
This Diagnostic Trouble Code is set during normal
ATC operation. The Diagnostic Trouble Code will be
set only after the ATC control has been operating for
15 minutes. The control will compensate for the feed-
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HEATING AND AIR CONDITIONING
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