Action Taken:

ECM turns on "SERVICE SOON" light. ECM commands BCM to display "SERVICE SOON" message on CCDIC panel. ECM turns off both AIR management solenoids. ECM substitutes 40°C for MAT when coolant temperature is greater than or equal to 40°C. ECM uses coolant temperature for MAT when coolant temperature is less than or equal to 40°C.

The MAT sensor is a thermistor that varies its resistance with temperature. The MAP sensor is a 2-wire sensor with a 5-volt reference voltage coming from the ECM to sensor terminal "B" over circuit No. 472, and a sensor reference ground on terminal "A" over circuit No. 476.

As temperature of sensor increases, sensor resistance is lower. The monitored signal voltage from ECM to terminal "B" decreases as sensor temperature increases, current flows from terminal "B" through sensor element to terminal "A", sensor ground.

High temperature means low signal voltage on circuit No. 472. Low temperature means high signal voltage on circuit No. 472. Code EO37, shorted MAT sensor, sets because ECM assumes that MAT cannot be 142°C or greater with a coolant temperature of less than 105°C.

1. With a shorted sensor, ECM parameter ED05 should read 142°C or greater. If not, sensor is not shorted. See NOTES ON INTERMITTENTS.
2. Check for sensor short or circuit No. 472 shorted. If ECM parameter EDO5 stays at 142-151°C with sensor unplugged, short is in circuit No. 472.
3. Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK before ECM is replaced.
4. MAT sensors can be damaged by a backfire in the intake. If vehicle has had more than one MAT sensor replaced, check for signs of backfire or high intake manifold temperatures due to improper valve train operation.