MPI –
Troubleshooting
13-10
Code No. 21 Engine coolant temperature sensor system
Probable cause
Range of Check
D
Ignition switch: ON
D
Excluding 60 seconds after the ignition switch is turned to ON or immediately
after the engine starts.
Set conditions
D
Sensor output voltage is 4.6 V or more (corresponding to an engine coolant
temperature of –45
_
C or less) for 4 seconds.
or
D
Sensor output voltage is 0.1 V or less (corresponding to an engine coolant
temperature of 140
_
C or more) for 4 seconds.
D
Malfunction of the engine coolant temperature sensor
D
Improper connector contact, open or short-circuited
harness wire of the engine coolant temperature sensor
circuit
D
Malfunction of the engine-ECU
Range of Check
D
Ignition switch: ON
D
Engine speed is approx. 50 r/min or more
Set conditions
D
The sensor output voltage increases from 1.6 V or less (corresponding to an
engine coolant temperature of 40
_
C or more) to 1.6 V or more (corresponding
to an engine coolant temperature of 40
_
C or less).
D
After this, the sensor output voltage is 1.6 V or more for 5 minutes.
Check the engine coolant temperature
sensor. (Refer to P.13-32.)*
NG
Replace
OK
Measure at the engine coolant temper-
ature sensor connector A-38.
D
Disconnect the connector, and
measure at the harness side.
D
Voltage between 1 and earth
(Ignition switch: ON)
OK: 4.5– 4.9 V
D
Continuity between 2 and earth
OK: Continuity
NG
Check the following connector:
B-62
NG
Repair
OK
Check trouble symptom.
NG
Check the harness wire between the
engine-ECU and the engine coolant
temperature sensor connector.
NG
Repair
OK
Replace the engine-ECU.
Check the following connector:
A-38
OK
Check trouble symptom.
NG
Replace the engine-ECU.
NG
Repair
OK
NOTE
*:
Refer to Workshop Manual for LANCER EVOLUTION-IV and EVOLUTION-V (Pub. No. S9806CNCP9).