ing any button except the A/C button or turning
a knob will end the diagnostic test without
showing the rest of the trouble codes. There
also may be other trouble codes stored in the
BCM not related to the Climate Control System.
These codes can only be found using the
DRBIIIt scan tool.
ERASING DIAGNOSTIC TROUBLE CODES (DTC’s)
Diagnostic trouble codes can be cleared from the
memory two ways:
• The DRBIIIt scan tool
• Power to the BCM can be disconnected for ten
minutes by disconnecting the battery negative
remote cable.
If the scan tool is to be used, refer to the proper
LH Body Diagnostic Procedures Manual.
CAUTION: Fault code 26 can be created if the
in-car sensor thermistor is disconnected while the
BCM is operating. This can happen by disconnect-
ing connectors from the BCM or the ATC Control
Head when the battery is connected (even if the
ignition switch is OFF). To correct, clear the fault
code 26 from the BCM.
HEATER PERFORMANCE TEST
PRE-DIAGNOSTIC PREPARATIONS
Review Safety Precautions and Warnings in this
group before performing the following procedures.
Check the coolant level, drive belt tension, vacuum
line connections, radiator air flow and fan operation.
Start engine and allow to warm up to normal tem-
perature.
WARNING: DO NOT REMOVE RADIATOR CAP
WHEN ENGINE IS HOT, SEVERE PERSONAL
INJURY CAN RESULT.
If vehicle has been run recently, wait until engine
is cool before removing cap. Squeeze the radiator
hose to check temperature, and for pressure in the
system. If the hose is very firm, allow time to cool
down. Place a rag over the cap and turn it to the first
safety stop. Allow pressure to escape through the
overflow tube. When the system stabilizes, remove
the cap completely.
MAXIMUM HEATER OUTPUT: TEST AND ACTION
Engine coolant is provided to the heater system by
two 19 mm (3/4 inch inside diameter) heater hoses.
With engine idling at normal running temperature,
set the control to maximum heat, floor, and high
blower setting. Using a test thermometer, check the
air temperature coming from the floor outlets. Refer
to Temperature Reference Table.
If the floor outlet air temperature is insufficient,
refer to Group 7, Cooling Systems for specifications.
Both heater hoses should be HOT to the touch (cool-
ant return hose should be slightly cooler than the
supply hose). If coolant return hose is much cooler
than the supply hose, locate and repair engine cool-
ant flow obstruction in heater system.
POSSIBLE LOCATIONS OR CAUSE OF
OBSTRUCTED COOLANT FLOW
(1) Pinched or kinked heater hoses.
(2) Improper heater hose routing.
(3) Plugged heater hoses or supply and return
ports at cooling system connections, refer to Group 7,
Cooling System.
(4) Plugged heater core.
(5) Air locked heater core.
(6) If coolant flow is verified and outlet tempera-
ture is insufficient, a mechanical problem may exist.
POSSIBLE LOCATION OR CAUSE OF INSUFFICIENT
HEAT
(1) Obstructed cowl air intake.
(2) Obstructed heater system outlets.
(3) Blend-air door not functioning properly.
TEMPERATURE CONTROL
If temperature cannot be adjusted with the TEMP
knob/button on the control panel, the following could
require service:
(1) Blend-air door binding.
(2) Faulty blend-air door motor.
(3) Improper engine coolant temperature.
(4) Faulty Instrument Panel Control.
(4) Refer to the appropriate LH Body Diagnostic
Procedures Manual.
SUN SENSOR
The sun sensor is located so the sun hits the sen-
sor in the same way that it hits the driver and the
passenger. It is important that the area in front of
TEMPERATURE REFERENCE TABLE
Ambient Temp. Minimum
Floor
Outlet
Temp.
Celsius Fahrenheit Celsius Fahrenheit
15.5° 60° 62.2° 144°
21.1° 70° 63.8° 147°
26.6° 80° 65.5° 150°
32.2° 90° 67.2° 153°
24 - 10 HEATING AND AIR CONDITIONING LH
DIAGNOSIS AND TESTING (Continued)
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