ECM Code EO37: Shorted Mat Sensor Circuit: Action:

ECM turns on SERVICE ENGINE SOON light. ECM substitutes 104°F (40°C) for MAT when coolant temperature is greater than or equal to 104°F (40°C). ECM uses coolant temperature for MAT when coolant temperature is less than or equal to 104°F (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. 469.

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 288°F (142°C) or greater with a coolant temperature of less than 221°F (105°C).

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

Test Number 1) With a shorted sensor, ECM parameter ED05 should read 148°C or greater. If not, sensor is not shorted. See NOTE ON INTERMITTENTS.

Test Number 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.

Test Number 3) 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.

Test Number 4) Fault is most likely at ECM connector or ECM. See CHART C1, ECM REPLACEMENT CHECK before ECM is replaced.