Coolant Temperature Override (CTO) Switch
NOTE:
Engine coolant temperature must be below 100°F (38°C) to perform this test.
- Check vacuum lines for leaks and correct routing. Disconnect vacuum line at back pressure sensor (if equipped) or at EGR valve, and attach this line to vacuum gauge.
- Operate engine at 1500 RPM. No vacuum should be indicated on gauge. If vacuum is shown, replace CTO switch.
- Idle engine until coolant temperature exceeds 115°F (46°C) on 6-cylinder and V8 engines.
- Accelerate engine to 1500 RPM. Carburetor ported vacuum should be shown on gauge. If not, replace CTO switch.