A water temp sensor
located at heater unit detects coolant temperature. It contains negative
type themistor whoses resistance value is in inverse proportion to
temperature. Resistance of watersensor that varies with temperature makes
signal voltage of A/C ECU change. In this way A/C ECU detects temperature.
Signal of water sensor is used for cold engine lockout control - When the
driver operates the heater before the engine is warmed up enough, to
prevent driver from unpleasantness of cold air. the heater control unit
reduces blower motor speed until coolant temperature reaches the threshold
value.
The ECM sets DTC B1203
if there is a short circuit in water temp sensor signal harness or the
measured resistance value of the sensor is less than the threshold
value(1.27kΩ)
Item
|
Detecting
Condition
|
Possible Cause
|
DTC
Strategy
|
|
| •
|
Short Circuit in signal
harness |
| •
|
Faulty water temp.
Sensor |
| •
|
Faulty A/C control
unit | |
Threshold
value
|
|
Detecting
time
|
|
FAIL
SAFE
|
| •
|
Control with the value of
-2°C | |
※ Resistance value of
water temp sensor as a function of temperature.
Temperature(°C)
|
Resistance(kΩ)
|
Temperature(°C)
|
Resistance(kΩ)
|
-10
|
55.8
|
40
|
5.3
|
0
|
32.9
|
60
|
2.4
|
20
|
12.5
|
80
|
1.2
|
| 1. |
Connect scantool to Data Link
Connector(DLC). |
| 2. |
Warm up the engine to normal operating
temperature. |
| 3. |
Monitor DTC(Diagnostics Trouble Code) on the
scantool.
|
| 4. |
Is the same DTC displayed again?
|
|
▶ Go to "
Inspection/Repair " procedure .
|
|
|
▶ Fault is
intermittent caused by poor contact in the sensor's and/or
A/C-ECM connector or was repaired and A/C-ECM memory was not
cleared. Thoroughly check connectors for looseness,
poorconnection, bending, corrosion, contamination,
deterioration, or damage. Repair or replace as necessary and
go to "Verification of vehicle Repair"
procedure.
|
|
| 1. |
Many malfunctions in the electrical system are
caused by poor harness and terminals. Faults can also be caused by
interference from other electrical systems, and mechanical or
chemical damage. |
| 2. |
Thoroughly check connectors for looseness,
poor connection, bending, corrosion, contamination, deterioration,or
damage. |
| 3. |
Has a problem been found?
|
|
▶ Repair as
necessary and go to "Verification of Vehicle Repair"
procedure
|
|
|
▶ Go to
"Signal circuit Short Inspection"
procedure.
|
|
| Signal Circuit Short
Inspection |
| 2. |
A/C-ECU : Connect, Water temp. sensor :
Disconnect. |
| 3. |
Measure resistance between Signal(+) terminal
of Water temp. sensor harness connector and and chassis ground
.
|
| 4. |
Is "resistance" display near the specified
value?
|
|
▶ Go to "
Component inspection " procedure .
|
|
|
▶ Check for
short to ground in harness.
▶
Repair as necessary and then go to "Verification of Vehicle
Repair"
procedure.
|
|
| 2. |
A/C-ECU, Water temp. sensor :
Connect. |
| 3. |
Measure resistance between Signal(+) terminal
of Water temp. sensor harness connector and and Sensor ground
harness connector .(Component side)
Specification
: Refer the specifications in
fig.1
|
Temperature(°C)
|
Resistance(kΩ)
|
Temperature(°C)
|
Resistance(kΩ)
|
-10
|
55.8
|
40
|
5.3
|
0
|
32.9
|
60
|
2.4
|
20
|
12.5
|
80
|
1.2
|
※ Specifications : Resistance value of water
temp sensor as a function of temperature.
※ The actual value may differ from it
according to various engine
condition. |
| 4. |
Is "resistance" display near the specified
value?
|
|
▶ Go to
"Check A/C-ECU" procedure
|
|
|
▶
Substitute with a known-good Water temp. sensor and check for
proper operation. If the problem is corrected, replace Water
temp. sensor and then go to "Verification of Vehicle Repair"
procedure.
|
|
Check A/C-ECU
| 2. |
A/C-ECU : Connect, Water temp. sensor :
Disconnect. |
| 3. |
Ignition "ON"(ENGINE
"OFF"). |
| 4. |
Measure voltage between Signal(+) terminal of
Water temp. sensor connector and and chassis ground .(Component
side)
Specification
: approx. 5V
| |
| 5. |
Is "voltage" display near the specified
value?
|
|
▶ Check
connectors for looseness, poor connection, bending, corrosion,
contamination, deterioration, or damage. Repair or replace as
necessary and then go to "Verification of Vehicle Repair"
procedure.
|
|
|
▶
Substitute with a known-good A/C-ECU and check for proper
operation. If the problem is corrected, replace A/C-ECU and
then go to "Verification of Vehicle Repair"
procedure.
|
|
| Verification Of Vehicle
Repair |
After a repair, it is
essential to verifying that the fault has been corrected.
| 1. |
Connect scan tool and select "Diagnostic
Trouble Codes(DTCs)" mode. |
| 2. |
Using scantool, Clear
DTC. |
| 3. |
Operate the vehicle within DTC Enable
conditions in General information. |
| 4. |
Are any DTCs present?
|
|
▶ Go to the
applicable troubleshooting procedure.
|
|
|
▶ System is
performing to specification at this
time.
|
|
