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Fault Code 23 - intake air temp sensor voltage too high or low
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Code 23 indicates that the PCM has detected a problem with the air charge temperature (IAT) sensor circuit. This code indicates that the computer has detected a signal voltage from this circuit of more than 4.98 or less than 0.06. In other words, the temperature of the charge air (air in the manifold) or throttle body is either extremely high or extremely low.
One of the wires to the air temperature sensor should always have 0 volts. The other should have a voltage between 0.5 and 4.5. If the reading is in that range, the air temperature sensing circuit is probably working correctly. If the voltage also changes when the temperature of the air changes, then that proves the circuit is working.
Begin testing the circuit by turning the ignition switch off and disconnecting the air temperature sensor wiring harness. Measure the resistance of the IAT - it should be in the range specified in the chart below. If it is not, the sensor is probably bad.
Connect a digital voltmeter across the terminals of the harness side of the connection. Turn the ignition switch back on. The voltmeter should read 5 volts. If the voltmeter does read 5 volts, replace the air sensor. If it does not read 5 volts, there is a problem in the air sensor wiring harness or the PCM.
Next test the 5-volt reference. With the ignition switch still on, connect the voltmeter between the black and red wire on the IAT connector and the battery negative terminal. The voltmeter should read 5 volts. If it does not, disconnect the battery, remove the PCM connector, and check for continuity in the wiring harness between the IAT connector and pin 15 of the PCM connector.
If the 5-volt reference is good, turn the ignition switch off. Connect the digital voltmeter between the positive terminal of the battery and the black and light blue wire on the IAT connector. The voltmeter should read 12 volts. If it does not, disconnect the battery, remove the PCM connector, and check ground continuity between the IAT connector and pin 4 of the PCM connector.
If no wiring problems are found, check the PCM connectors for corrosion, and reconnect. Reconnect the battery and test the circuit again. If the problem still exists, the PCM is probably bad.
The air temperature sensor is very similar to a coolant temperature sensor. The primary difference is that the protective cover over the thermister is open to allow the air to come into direct contact with the sensing element.
Last Update: August 8, 2001