2/28/22, 9:37 PM
Powertrain Controls - ECM/PCM (ALL Diagnostic Trouble Codes ( DTC )) - ALLDATA Repair
1990 Cadillac Fleetwood Brougham V8-350 5.7L
Vehicle > ALL Diagnostic Trouble Codes ( DTC ) > Testing and Inspection > Manufacturer Code Charts > DTC 23
POWERTRAIN CONTROLS - ECM/PCM
Code 23 Chart
Wiring Diagram For MAT/IAT Sensor
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2/28/22, 9:37 PM
Powertrain Controls - ECM/PCM (ALL Diagnostic Trouble Codes ( DTC )) - ALLDATA Repair
CIRCUIT DESCRIPTION:
The Manifold Air Temperature (MAT) Sensor is a thermistor that controls the signal voltage to the ECM. The ECM
applies a reference voltage (about 5.0 volts) on circuit 472 to the sensor. When the air is cold, the sensor (thermistor)
resistance is high, therefore the ECM will sense a high signal voltage. If the air is warm, the sensor resistance is low,
therefore the ECM will see a low voltage.
TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.
1. A Code 23 will set under the following conditions:
a. The engine has been running longer than one minute.
b. The signal voltage indicates a MAT reading of less than -30°C (-22°F) for 12 seconds.
2. A Code 23 will set due to an open sensor, wire, or connection. This test will determine if the wiring and ECM are
OK.
3. This will determine if the MAT sensor signal circuit 472 or the MAT sensor ground circuit 452 is open.
DIAGNOSTIC AIDS:
1. If the engine has been allowed to cool to ambient temperature, coolant and MAT temperatures may be checked
with a "Scan" tool. The readings should be close to each other. After the engine starts, the MAT will increase due to
Thermic operation and underhood temperatures.
2. A "Scan" tool indicates the temperature of the air surrounding the air cleaner because the MAT sensor is mounted
to the air cleaner housing.
3. Carefully check harness and connections for possible open circuits 472 or 452. If Code 23 is intermittent, see
DIAGNOSIS BY SYMPTOM.
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