Manifold Air Temperature/Intake Air Temperature Sensor

Code 23 Manifold Air Temperature Sensor Circuit, intake air temp sensor out of range, low

Manifold Air Temperature/Intake Air Temperature Sensor

§  Operation

§  Removal & Installation

§  Testing

Operation

The MAT or IAT sensor (as equipped), is a thermistor (resistor which changes value based on temperature) mounted either in the air intake snorkel or the manifold (depending on the application). Low intake air temperatures produce a high resistance—100,000 ohms at -40°F (-40°C), while high temperatures cause low resistance—70 ohms at 266°F (130°C).

The control module provides a 5 volt reference signal to the sensor through a resistor in the module and measures the voltage. The voltage will be high when the air is cold and low when the air is hot. By measuring the voltage, the control module knows the intake/manifold air temperature.

The air temperature signal is used by the control module to delay EGR until the temperature reaches approximately 40°F (5°C). The control module also uses the signal to retard ignition timing during high air temperatures.

Removal and installation of the MAT/IAT sensor is covered in Section 3 of this manual. Please refer there for further information.

Testing

Refer to Engine Coolant Temperature Sensor testing.

Using an ohmmeter, measure the resistance between the terminals. Refer to the appropriate chart for your engine. If the resistance is not as specified, replace the sensor.

Removal & Installation

Except 3.1L Engine

1. Disconnect the negative battery cable.
2. Make sure ignition switch is in the OFF position.
3. Detach the electrical connector from the IAT sensor.

1. Carefully remove the sensor from the intake manifold or air cleaner housing.

To install:

1. Coat the sensor threads with sealer 9985253 or equivalent, then install the IAT sensor in the intake manifold.
2. Tighten the sensor to 6 ft. lbs. (8 Nm)
3. Attach the electrical connector to the sensor.
4. Connect the negative battery cable.

Code 32 Exhaust Gas Recirculation System, egr circuit fault.

Exhaust Gas Recirculation System

§  Description & Operation

§  Removal & Installation

§  Testing

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Testing

Refer to the appropriate chart to test the EGR system.

Code 34 Manifold Absolute Pressure Sensor Malfunction, map sensor signal out of range, low.

Manifold Absolute Pressure Sensor

§  Operation

§  Removal & Installation

§  Testing

Operation

The Manifold Absolute Pressure (MAP) sensor measures the changes in intake manifold pressure, which result from engine load and speed changes and converts this information to a voltage output. It is found on all engines except the 3.0L (VIN L) and 3.3L (VIN N). The MAP sensor reading is the opposite of a vacuum gauge reading: when manifold pressure is high, MAP sensor value is high and vacuum is low. A MAP sensor will produce a low output on engine coastdown with a closed throttle while a wide open throttle will produce a high output. The high output is produced because the pressure inside the manifold is the same as outside the manifold, so 100% of the outside air pressure is measured.

The MAP sensor is also used to measure barometric pressure under certain conditions, which allows the ECM to automatically adjust for different altitudes.

The MAP sensor changes the 5 volt signal supplied by the computer control module (ECM or PCM as applicable), which reads the change and uses the information to control fuel delivery and ignition timing.

Removal and installation of the manifold absolute pressure sensor is covered in Section 3 of this manual. Please refer there for further information.

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Testing

Animations and Tech Tips

Click to view: Testing a MAP sensor

1. Backprobe with a high impedance voltmeter at MAP sensor terminals A and C.
2. With the key ON and engine off, the voltmeter reading should be approximately 5.0 volts.
3. If the voltage is not as specified, either the wiring to the MAP sensor or the PCM may be faulty. Correct any wiring or PCM faults before continuing test.
4. Backprobe with the high impedance voltmeter at MAP sensor terminals B and A.
5. Verify that the sensor voltage is approximately 0.5 volts with the engine not running (at sea level).
6. Record MAP sensor voltage with the key ON and engine off.
7. Start the vehicle.
8. Verify that the sensor voltage is greater than 1.5 volts (above the recorded reading) at idle.
9. Verify that the sensor voltage increases to approximately 4.5. volts (above the recorded reading) at Wide Open Throttle (WOT).
10. If the sensor voltage is as specified, the sensor is functioning properly.
11. If the sensor voltage is not as specified, check the sensor and the sensor vacuum source for a leak or a restriction. If no leaks or restrictions are found, the sensor may be defective and should be replaced.