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.
1991 Mercury Cougar LS, 3.8 4FACTORY OEM SERVICE PROCEDURE
Code E5
- Disconnect harness connector at sensor and both connectors at temperature control assembly. Using an ohmmeter, measure resistance across sensor terminals. Sensor is a photodiode and produces resistance based on available light.
- If ohmmeter reading is greater than zero, sensor is okay. If ohmmeter reading is zero, sensor is shorted. Replace sensor. If sensor is okay, check for short to ground or short circuit in wiring harness. Repair as necessary. See WIRING DIAGRAM .
Factory Service Tools
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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.
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