Engine Coolant Temperature (Ect) Sensor; Testing And Replacing - BMW 5251 Service Manual

130-1 0
Fuel
Injection
Remove MAF sensor:
Release clips from air filter housing (A).
Disconnect harness connector (B).
Loosen intake boot clamp (C) and remove MAF sensor.
Note large sealing O-rings.
Installation is reverse of removal.
No adjustment to MAF sensor is possible.
Check intake hoses for cracks and vacuum leaks.
Engine coolant temperature (ECT) sensor,
testing and replacing
R
1
-4
The ECT sensor is located below cylinder 1 intake port
The ECT sensor is a dual temperature sensor. One circuit
provides coolant temperature information to the ECM while
the other circuit provides coolant temperature information to
the instrument cluster.
The ECM determines the correct ignition timing and airlfuel
mixture required for the engine by monitoring an applied volt-
age (5 vdc) to the sensor. The voltage drop across the sensor
varies as the coolant temperature (sensor resistance) chang-
es.
NOTE-
The ECT sensor is an NTC (negative temperature coeffi-
cient) type sensor. in other words, as the temperature rises,
resistance through the sensor decreases.
If the ETC sensor input is faulty or non-plausible, the MIL is il-
luminated when OED II fault criteria are exceeded. The ECM
assumes asubstitute value (80°C1 176°F) to maintainengine
operation. The ignition timing is set to a conse~ativelsafe ba-
sic setting.
-
Check ECT sensor resistance using a multimeter at sensor
terminals.
-
WARNING
-
Due to risk of personal injury, be sure the engine is cold be-
fore disconnecting or reconnecting ECT sensor.
ECT
sensor resistance
@ 20" C (68°F) 2.2
-
2.7
Temperature gauge sensor resistance
@
20°C
(~B"F)( 6.7
k