DFI ECM Tests W/Codes: Action:

ECM turns on "ENGINE CONTROL SYSTEM" 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 is greater than or equal to 40°C. ECM uses coolant temperature for MAT when coolant temp is less than or equal to 40°C.

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

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

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

NOTE: Test numbers refer to test numbers on diagnostic chart.

With a shorted sensor, ECM parameter Code ED05 should read 142°C or greater. If not, sensor is not shorted. See NOTES ON INTERMITTENTS.
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.
Fault is most likely at ECM connector or ECM. See CHART C1 - ECM REPLACEMENT CHECK, before ECM is replaced.
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.