Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSJEEP1987COMANCHE LAREDO, 4.0 M, RWD, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMEGR FUNCTION TESTINGTESTINGCOOLANT TEMPERATURE OVERRIDE (CTO) SWITCH
1987 Jeep Comanche Laredo, 4.0 M, RWD, Automatic
Coolant Temperature Override (CTO) Switch
1987 Jeep Comanche Laredo, 4.0 M, RWD, AutomaticSECTION 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 backpressure 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 100°F (38°C) on 4-cylinder engines, or 115°F (46°C) on 6-cylinder and V8 engines.
- Raise engine speed to 1500 RPM. Ported vacuum should be shown on gauge. If not, replace CTO switch.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.