DTC 25

Fig. 006 - WIRING DIAGRAM for Code 25 Manifold Air Temperature (Signal Voltage Low). VIN S:

CODE 25, MANIFOLD AIR TEMPERATURE (MAT) SENSOR

(SIGNAL VOLTAGE LOW)
The Manifold Air Temperature Sensor uses a thermistor to control the signal-voltage to the ECM. The ECM applies a voltage on CKT 996 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.
Code 25 will set if:
a. Signal voltage indicates a manifold air temperature greater than 135°C for 3 seconds.
b. Time since engine start is 8 minutes or longer.
c. Due to the conditions necessary to set a Code 25 the check engine light will only remain on while the signal is low and vehicle speed is present.

Code 25 Manifold Air Temperature (Signal Voltage Low):

1. If voltage is above 4 volts, the ECM and wiring are OK.
2. If resistance is less than 185 ohms, replace the sensor.