23A LO Temperature Indicated

Code 23A MAT Circuit:

Code 23A MAT Diagnostic Chart (Low Temp Indicated):

CIRCUIT DESCRIPTION:

The Manifold Air Temperature (MAT) sensor uses a thermistor to control the signal voltage to the ECM. The ECM applies a voltage (4-6V) through CKT CKT 472 to the sensor. When manifold air is cold, the sensor (thermistor) resistance is high, therefore, the ECM will see a high signal voltage. As the air warms, the sensor resistance becomes less, and the voltage drops.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. This step checks to see if Code 23A is the result of a hard failure or an intermittent condition. A Code 23A will set if:

a. Engine has been running for longer than 255 SECONDS.
b. Signal voltage indicates an MAT temperature less than -30°C.

2. This test simulates conditions for a Code 23B (High Temperature Indicated). If the Scan tool displays a high temperature, the ECM and wiring are OK.

3. This step checks continuity of CKTs 472 and 452. If CKT 452 is open, there may also be a Code 21A.

DIAGNOSTIC AIDS:

If the engine has been allowed to cool to an ambient temperature (overnight), coolant and MAT temperatures may be checked with a Scan tool and should read close to each other. A Code 23A will result if CKTs 472 and 452 become open. If Code 23A is intermittent,
Intermittant Check Procedure