MACS Service Reports - 2016 - JUL4

cal late model gas engine application are:

(14°F).
6. The DTC runs once per ignition cycle when
the above conditions are met.

1. DTC P0102, P0103, P0111, P0112, P0113,
P0114, P0117, P0118, P0119, P0121,
P0122, P0123, P0221, P0222, P0223, P0335,
P0336, P0501 or P111E are not set.
2. The increase in ECT after engine start is
within a calibrated range.
3. The engine not run time is greater than 30
minutes.
4. The start-up ECT is between -10 and +75°C
(14-167°F).
5. The start-up IAT is warmer than -10°C

Other non-continuous monitors such as catalytic converter efficiency and evaporative emissions
monitors have an even greater set of criteria in order for the OBD II trip to take place for that particular monitor. The fuel level may have to be a within
a certain level range (typically between 15 % and 85
%) for the evap monitor to run for example. Another
term is OBD II "Drive Cycle." A drive cycle consists
of meeting all the criteria to run all monitors. ■

ANATOMY OF AN ECT SENSOR / SENSOR COMMON WOES
An ECT sensor (Engine Coolant Temperature) is a
simple thermistor. In the case of the ECT that would
basically be a resistor that changes resistance as it
reacts to changes in the temperature of the coolant it is suspended in. Most all ECTs in use today
are of the NTC (Negative Temperature Coefficient)
design. When temperatures go up the sensor 's resistance goes down and vice versa. (Fig. 4) The
April 2015 MACS Service Report described in detail

ant through the sensor wiring. Contaminate coolant can also lead to an acidic nature of the coolant
which can then cause the creation of voltage in the
cooling system. Similar to a galvanic battery cell
in nature, acidic coolant with the dissimilar metals
found in most cooling systems can create a rise in
coolant voltage potential that not only causes cooling system damage due to corrosion but also create
an electrical problem for sensor accuracy. (Fig. 6)
Measuring the voltage from chassis ground to the
coolant itself by simply dipping the positive probe

Figure 4: Any NCT (Negative Coefficient Temp) sensor looks like this regarding it's affect on the 5 volts that the module sends it. The lower the temperature
the higher the resistance. The higher the resistance, the more voltage the sensor
drops.

Figure 6: The ground for ECTs can float up when coolant becomes corrosive
thereby creating inaccurate ECT values read by the ECM. This may or may
not be bad enough to set a sensor 'plausibility' DTC.

various thermistors used in the HVAC applications.
Their pattern failures include the sensor body being insulated from accurate coolant temperature
measurement (coolant corrosion on the sensor) as
well as sensor leakage through the electrical connector which can lead to the "wicking" of cool-

of your voltmeter is a time honored practice for
catching corrosion that can lead to trouble. DC voltage higher than 0.5 volts is the high limit. Higher
than that and it is time for a very thorough cooling
system flush. Engine coolant temperature accuracy
can also be adversely affected if coolant is not sur-

July 2016

MACS Service Reports

Table of Contents for the Digital Edition of MACS Service Reports - 2016