Diagnostic Aids
The Scan tester reads engine temperature in degrees centigrade. After engine is started, temperature should rise steadily to about 194°F (90°C), then stabilize when thermostat opens. When a Code 15 is set, the ECM will turn on engine cooling fan. A Code 15 will result if circuits No. 410 or 452 are open. If Code 15 is intermittent, see INTERMITTENTS in TESTS W/O CODES article.