KC-613

4/29/22, 11:02 AM
Article
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Ambient Air Temperature Reading In Instrument
Cluster ( IC ) Is Different From The Reading in
Premium Tech Tool ( PTT ); Outside Temperature
Prevents Guided Diagnostics ( GD ) Operations For
the Exhaust Aftertreatment System ( EATS ) From
Being Perfo
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Internal Content
Overview
The Ambient Air Temperature signal is monitored by the Instrument
Cluster. The Cluster provides a live reading on the Driver Information
Display ( DID ) and should reflect the current outside air temperature.
Modules that require the ambient tempurature reading, namely the
Engine Management System ( EMS ), receive the value from the
instrument cluster via the J1939 Data Link. Premium Tech Tool reads
the Ambient Temperature value from the EMS.
To prevent false readings due to heat soak at the ambient
temperature sensor, the EMS will lock the ambient temperature value
when coolant temperature exceeds 50°C (122°F). The only point when
temperature is updated with coolant and oil temperatures above 50°
is after an hour of continuous operation, which occurs along with an
engine fan activation. In addition, if the EMS is showing low coolant
and oil temperatures and the ambient temperature value changes
significantly in a short period of time, the EMS may consider the
reading to be incorrect.
If a chassis is pulled into a shop for diagnostic work while the engine
is still hot, the EMS may still have the ambient temperature value
locked at the temperature the sensor reported when the coolant
temp originally exceeded 50°C. Conversely, if a chassis is started cold
and immediately pulled into a warm shop, the sudden ambient
temperature change when compared to coolant and oil temperature
reading and rate of change may cause the EMS to disregard the
ambient temperature reading as incorrect.
Resolution
A chassis with a warm engine should be allowed to cool down with
UI
; Live
the engine Off until coolant and oil temperatures drop below 40°C
(104°F) before it is pulled into the shop Lifting the hood will help to
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4/29/22, 11:02 AM
Article
(104 F) before it is pulled into the shop. Lifting the hood will help to
accelerate cool down.
A chassis with a cold engine should be allowed to run until coolant
and oil temperatures reach 20°C (68°F) before it is pulled into the
shop. Engine oil temperature can be monitored from the Driver
Information Display ( DID ) This will put oil and coolant sensor
readings at approximately room temperature and the ambient
temperature change from being pulled inside will not be considered
incorrect.
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k06837732
volvo
cu15
cu12 cng
cu9 cng
cu9
mack
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