Pinpoint Test DN: Motor Electronics Coolant Temperature (MECT) Sensor: Introduction

WARNING: TO PREVENT THE RISK OF HIGH-VOLTAGE SHOCK, ALWAYS FOLLOW PRECISELY ALL WARNINGS AND SERVICE INSTRUCTIONS, INCLUDING INSTRUCTIONS TO DEPOWER THE SYSTEM. THE HIGH-VOLTAGE HYBRID SYSTEM UTILIZES APPROXIMATELY 300 VOLTS DC, PROVIDED THROUGH HIGH-VOLTAGE CABLES TO ITS COMPONENTS AND MODULES. THE HIGH-VOLTAGE CABLES AND WIRING ARE IDENTIFIED BY ORANGE HARNESS TAPE OR ORANGE WIRE COVERING. ALL HIGH-VOLTAGE COMPONENTS ARE MARKED WITH HIGH-VOLTAGE WARNING LABELS WITH A HIGH-VOLTAGE SYMBOL. FAILURE TO FOLLOW THESE INSTRUCTIONS MAY RESULT IN SERIOUS PERSONAL INJURY OR DEATH.

NOTE: Carefully check the motor electronics cooling system integrity. Over-temperature diagnostic trouble codes (DTCs) can be stored as a result of extreme driving conditions. Under normal operating conditions, the motor electronics coolant temperature should not exceed 65°C (150°F) and maintain a temperature of approximately 11°C (20°F) over ambient temperature during a steady cruise above 65 km/h (40mph).

This pinpoint test is intended to diagnose the following:

MECT (12B579)
harness circuits: MECT, VREF, and SIGRTN
powertrain control module (PCM) (12A650)

Voltage values calculated for VREF = 5 volts. These values can vary by 15% due to sensor and VREF variations.

Fig 1: Motor Electronics Coolant Temperature (MECT) Sensor Temperature And Voltage Graph

Courtesy of FORD MOTOR CO.

TEMPERATURE SENSOR VOLTAGE AND RESISTANCE SPECIFICATIONS

Temperature		Temperature Sensor Values
°C	°F	Voltage	Resistance (K ohms)
120	248	0.28	1.18
110	230	0.36	1.55
100	212	0.47	2.07
90	194	0.61	2.80
80	176	0.80	3.84
70	158	1.05	5.37
60	140	1.37	7.70
50	122	1.77	10.97
40	104	2.23	16.15
30	86	2.74	24.27
20	68	3.26	37.30
10	50	3.73	58.75
0	32	4.14	95.85
-10	14	4.45	160.31

Fig 2: Motor Electronics Coolant Temperature (MECT) Sensor Connector

Courtesy of FORD MOTOR CO.

MECT SENSOR CONNECTOR PINS REFERENCE CHART

Pin	Circuit
2	SIGRTN (Signal Return)
1	MECT (Motor Electronics Coolant Temperature)

Fig 3: Powertrain Control Module (PCM) Connector

Courtesy of FORD MOTOR CO.

PCM CONNECTOR PINS REFERENCE CHART

Pin	Circuit
B66	VREF (Reference Voltage)
T40	SIGRTN (Signal Return)
T29	MECT (Motor Electronics Coolant Temperature)