DTC 25

Fig. 009 - WIRING DIAGRAM for Code 25 Manifold Air Temperature. VIN J:

CODE 25

MANIFOLD AIR TEMPERATURE (MAT) SENSOR

1.8L TURBO "J" SERIES

FUEL INJECTION (PORT)

The Manifold Air Temperature Sensor uses a thermistor to control the signal-voltage to the ECM. The ECM applies a voltage on CKT 472 to the sensor. When manifold air is cold the sensor (thermistor) resistance is high, therefore the ECM will see high signal voltage.
As the air warms, the sensor resistance becomes less, and the voltage drops. At normal engine operating temperature, the voltage will measure about 1 to 2 volts at the ECM terminal C-12.
Code 25 will set if Signal voltage indicates a manifold air temperature above - 135°C (275°F) for more than 2 seconds.
Possible causes of a Code 25 are:
a. Faulty wiring or terminals
b. CKT 472 shorted to ground
c. A shorted MAT sensor
d. A faulty ECM
Manifold air temperature is one of the inputs used to control:
a. Fuel delivery.
b. Engine Timing (EST)
c. Idle (IAC)

Fig. 008 - Chart - Code 25 Manifold Air Temperature (Signal Voltage Low):

1. If voltage is above 4 volts, the ECM and wiring are OK.
2. If checking resistance at the manifold air sensor is difficult because of sensor location, disconnect the ECM connectors and check resistance between harness connector terminals C-12 and A-11.