Diagnostic Aids

The coolant temperature sensor, in rare cases, may fail to indicate the correct coolant temperature without setting a malfunction code (Code 14 or 15). This could result in turning on the hot light without having an overheating condition. It could also result in engine overheating without turning on the hot light. Check coolant sensor temperature-to-resistance values.

Monitor the voltage of each terminal while moving related harness connectors, including ECM harness. If the fault is induced, the voltage will change. This may help locate intermittent problems. If code reappears with no apparent problems, replace ECM.

Fig 1: Code 26 Troubleshooting Flowchart (3.8L W Body W/ECM)

Courtesy of GENERAL MOTORS CORP.

B) (3.8L W Body Without ECM-Controlled Temp Light) This determines which circuit is out of specification. If all circuits check out okay, the in-line resistor (used in place of the hot light) and related wiring should be checked. In-line resistor is taped into engine harness between right power center and ECM pigtail, about 2 inches from ECM pigtail junction.

Fig 1: Code 26 Troubleshooting Flowchart (3.8L W Body W/O ECM)

Courtesy of GENERAL MOTORS CORP.

This determines if the problem is the circuit or the component. Factory-installed ECM has an internal fuse and it's unlikely ECM needs replacing.

Fig 2: Code 26 Troubleshooting Flowchart 2 Of 2 (3.8L W Body)

Courtesy of GENERAL MOTORS CORP.