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Level 21

Thermistors


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Resistor
A thermistor is a type of ___ whose resistance varies significantly with temperature, more so than in standard resistors.
Negative Temperature Coefficient
Nearly all automotive thermisters are NTC. NTC means ___ ___ ___
Resistance, Increases
A NTC sensor will vary its ____ in relation to temperature, it decreases as its temperature ___
Less, Rise
Vehicle wiring is more like PTC - when its cold there is ___ resistance, but once hot with increasing current its resistance will ___ .
Signal, Rises
For a thermister the 5v supply is also the ___ wire, this is pulled down towards ground as temp ___.
Output State Monitoring
The OSM circuit stands for ___ ___ ___. This is the internal PCM 10Mohm voltmeter circuit that reports on the signals received.
10Mohm
The OSM acts as a voltmeter with an internal impedance of ___. It doesn't support current flow.
Cold
A ___ thermistor will have greater resistance so we expect a high voltage reading near 4.5V
Hot
A ___ thermistor will have lower resistance so we expect a low voltage reading nearing 0v
Open, 5
If there is an ___ in the circuit then there will be no current flow so no voltage drop. So computer will always read ___V on the signal line
Step, Resistors
A ___ thermistor can have 2 different ___ to allow for more accuracy in reading the temperatures between cold and hot running.
Cold
Step thermistors will use a 10Kohm resistor for the ___ curve
Hot
Step thermistors will use a 1Kohm resistor for the ___ curve
Air Fuel, 15
The ECT sensor is the main input for calculating the __ ___ ratio when cranking, typical cold cranking injection duration could be as long as ___ms
Low, Flooded
If temperature is reading too ___ (5v) due to open in thermistor this will cause a hard hot start due to the plugs being ___ with fuel
Open, Stoichiometric
Faulty ECT sensor will cause the system to stay in ___ loop, emissions will be high as the computer only tries to achieve ___ in closed loop.
Cold, High
Faulty temp sensor reading too ___ can cause, a ___ idle when hot (auto choke) and hard hot start (flooding)
Warm
Faulty temp sensor reading too ___ can cause, a cold start and stall (too lean) and lean hesitation during warmup
Cold, 5
Compare the IAT and ECT when engine is ___, they should be within ___ degrees of each other
Substitute, Voltage
If a DTC fault is logged the PCM can ___ a temperature reading but the ___ will still read true. The PCM only substitutes values with a hard fault DTC
Unplug, 5
___ the sensor should create a ___V signal (-40 degrees on the scanner). Can then cross signal wire to the ground pin to test if it gets pulled down to 0v (126 degrees) correctly.
Shorted
If the signal is showing 0v all the time then unplug sensor, if signal line jumps to 5v then sensor is ___ pulling signal to ground.
5
If the signal is showing ___V (0 or 5) then check the sensors ground, if ground is good then either connector or thermistor is bad (open)
Current Limiting Resistor
The thermister circuit has an internal ____ ___ ___, means we can short the 5V temperature reference to ground without damaging the computer.
0.5, 1.5
A typical reading for a hot engine would be ___V to ___V
100
A ground voltage drop test should never be any higher then ___mV for sensors
Shorted
If we have 0V on both wires to thermister, unplugging sensor then brings one wire to 5V what is the problem. Thermistor is ___
B
If both pins at plugged in thermistor read 5V. Could this be A:Shorted thermistor, B:Open in ground wire or C:Open thermistor