Pcm Code EO37, Shorted Mat Sensor Circuit: Action:

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

With a shorted MAT sensor, PCM parameter ED05 should read 148°C or greater. If not, sensor is not shorted. See NOTE ON INTERMITTENTS.
Check sensor short or circuit No. 472 shorted. If PCM parameter EDO5 stays at 142-151°C with sensor unplugged, then circuit No. 472 is shorted to ground.
MAT sensors can be damaged by a backfire in the intake. If vehicle has had more than one MAT sensor replaced, check signs of backfire or high intake manifold temperatures due to improper valve train operation.
Fault is most likely at PCM connector or PCM. See PFI CHART C-1, PCM REPLACEMENT CHECK before PCM is replaced.