COOLING SYSTEM DIAGNOSIS CHART
CONDITION POSSIBLE CAUSES CORRECTION
TEMPERATURE GAUGE
READS LOW
1. Has a Diagnostic Trouble Code
(DTC) been set indicating a stuck open
thermostat?
1. Refer to Group 25, Emission Systems
for On-Board Diagnostics and DTC
information. Replace thermostat if
necessary.
2. Is the temperature sending unit
connected?
2. Check the temperature sensor
connector. Refer to Group 8E. Repair
connector if necessary.
3. Is the temperature gauge operating
OK?
3. Check gauge operation. Refer to
Group 8E. Repair as necessary.
4. Coolant level low in cold ambient
temperatures accompanied with poor
heater performance.
4. Check coolant level in the coolant
reserve/overflow tank and the radiator.
Inspect system for leaks. Repair leaks
as necessary. Refer to the Coolant
section of the manual text for
WARNINGS and CAUTIONS associated
with removing the radiator cap.
5. Improper operation of internal heater
doors or heater controls.
5. Inspect heater and repair as
necessary. Refer to Group 24, Heating
and Air Conditioning for procedures.
TEMPERATURE GAUGE
READS HIGH OR THE
COOLANT WARNING
LAMP ILLUMINATES.
COOLANT MAY OR MAY
NOT BE LOST OR
LEAKING FROM THE
COOLING SYSTEM
1. Trailer is being towed, a steep hill is
being climbed, vehicle is operated in
slow moving traffic, or engine is being
idled with very high ambient (outside)
temperatures and the air conditioning is
on. Higher altitudes could aggravate
these conditions.
1. This may be a temporary condition
and repair is not necessary. Turn off the
air conditioning and attempt to drive the
vehicle without any of the previous
conditions. Observe the temperature
gauge. The gauge should return to the
normal range. If the gauge does not
return to the normal range, determine
the cause for overheating and repair.
Refer to Possible Causes (2-20).
2. Is the temperature gauge reading
correctly?
2. Check gauge. Refer to Group 8E.
Repair as necessary.
3. Is the temperature warning
illuminating unnecessarily?
3. Check warning lamp operation. Refer
to Group 8E. Repair as necessary.
4. Coolant low in coolant reserve/
overflow tank and radiator?
4. Check for coolant leaks and repair as
necessary. Refer to Testing Cooling
System for Leaks in this Group.
5. Pressure cap not installed tightly. If
cap is loose, boiling point of coolant will
be lowered. Also refer to the following
Step 6.
5. Tighten cap
6. Poor seals at the radiator cap. 6. (a) Check condition of cap and cap
seals. Refer to Radiator Cap. Replace
cap if necessary.
(b) Check condition of radiator filler
neck. If neck is bent or damaged,
replace radiator.
DN COOLING SYSTEM 7 - 11
DIAGNOSIS AND TESTING (Continued)
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