Air Charge Temperature Sensor


The logic module uses the charge temperature sensor to monitor the temperature of the air/fuel mixture in the intake manifold.  It uses this information, in addition to the manifold pressure, to calculate the density of the air entering the engine.  This information is used to calculate how much fuel should be injected into the engine at WOT.  The 1984 style sensor used a thermistor/fixed resistor combination, which measures 5,290 ohms to 5,610 ohms at 77^F.  The fixed resistor increases sensor accuracy at high temperatures.  The 1985 and later sensor design is just the thermistor, which measures 9,120 ohms to 10,880 ohms at 77^F.  The voltage on both sensor designs should read about 2.5V at 77^F.  In 1988, the Turbo I engines no longer received this sensor.  The battery temperature and coolant temperature sensors were used to measure the incoming air since the turbo added a fairly consistent amount of heat to it.  Turbo II engines still received the sensor since the air charge temperature could vary based on the efficiency of the intercooler.

Fault Codes

This sensor is diagnosed similarly to the coolant temperature sensor.  If the sensor voltage is less than 0.157V or greater than 3.76V for 1984 models or less than 0.06V or greater than 4.98V for 1985 and later models, a fault code 23 is stored and the power loss light is turned on.  The system will enter limp-in mode and an air charge temperature of 70^F is assumed.

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Updated 12/17/2003.

Copyright © 1996-2003 Russ W. Knize.