Diagnostic Aids

If engine is allowed to cool overnight, coolant temperature sensor and MAT sensor should read close to each other, when measured with a scan tester. A Code 25 will also result if sensor signal circuit is shorted to ground.

CODE 25 ECM TERMINAL & CIRCUIT WIRING IDENTIFICATION

Application	ECM Terminal	Wire Color
2.5L
Signal	C12	Tan
MAT Ground	D2	Black/Orange

TEMPERATURE-TO-RESISTANCE VALUES ⁽¹⁾⁽²⁾

°F (°C)

Ohms

210 (100)

185

160 (70)

450

100 (38)

1800

70 (20)

3400

40 (4)

7500

20 (-7)

13,500

0 (-18)

25,000

-40 (-40)

100,700

⁽¹⁾	Measure resistance across sensor terminals.

⁽²⁾	Temperatures are approximates.

Fig 1: Code 25, Schematic, MAT Sensor Temp. High (2.5L)

Courtesy of GENERAL MOTORS CORP.

Fig 2: Code 25, Flow Chart, MAT Sensor Temp. High (2.5L)

Courtesy of GENERAL MOTORS CORP.