E037

TEST CONDITIONS
1. Codes EO14 and EO15 not set;
2. Coolant temperature less than or equal to 100°C.

FAILURE CONDITIONS
MAT equal to or greater than 148°C

ACTION TAKEN
1. ECM turns on "Engine Control System Fault" telltale;
2. ECM commands BCM to display "Service Soon" message on Driver Information Center (DIC);
3. AIR management system is disabled;
4. ECM substitutes 40°C for MAT when coolant is equal to or greater than 40°C;
5. ECM substitutes coolant temp for MAT when coolant temp less than or equal to 40°C.

DESCRIPTION
The MAT sensor is a thermistor, or variable resistor, that varies resistance based on temperature. The MAT sensor is a "Two-wire" sensor with a reference, or signal, voltage coming from the ECM to sensor pin B (CKT 472), and a sensor reference ground on Pin A (CKT 476). As the temperature of the sensor increases, resistance decreases. As the resistance decreases, the signal voltage from the ECM decreases due to less voltage drop across the MAT sensor. High temperature will result in low signal voltage on CKT 472 and low temperature will result in high signal voltage on CKT 472.

The ECM uses MAT information to correct the fuel delivery rate for the temperature of the air that is entering the intake manifold.

Code EO37 sets when the ECM sees a MAT sensor reading of 148°C when the coolant is less than 100°C.

Notes on Fault Tree
1. If the MAT sensor is shorted, ECM Data ED05 should read 148°C or greater. If it does not, then the sensor is not shorted, see Note on Intermittents.
2. Checking for sensor shorted or CKT 472 shorted to ground. If ECM Data ED05 stays at 142-151°C with the sensor unplugged, then CKT 472 is shorted to ground.
3. MAT sensors can be damaged by a backfire in the intake manifold. If the vehicle has had more than one MAT sensor replaced, check for signs of backfire or high intake manifold temperature due to improper valve train operation.
4. Fault is most likely at ECM connector or ECM. Before ECM is replaced, perform "ECM Replacement Check," Chart C-1. Chart C-1 Vehicle Will Not Enter Diagnostics

Notes on Intermittents
Manipulate CKT 472 wiring, the MAT sensor connector and the ECM connector while observing ECM Data ED05. If the failure is induced, the manifold air temperature will jump from its normal value to the shorted reading 142°C-151°C. Remove and replace both the MAT and ECM connectors and ensure that they are latched. If wiring and connectors check out ok, substitute a known good MAT sensor and retest.