Diagnostic Aids

If the engine is allowed to cool overnight, the coolant and MAT sensors, when measured with a "Scan" tester, should read close to each other.

When Code 15 is set, the ECM will turn on the cooling fan. A Code 23 will also result if circuits No. 472 or 469 become open.

Fig 1: Code 23 Schematic, MAT Sensor Temp Low

Fig 2: Code 23 Flow Chart, MAT Sensor Temp Low