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 MANUALSFORD1988AEROSTAR VAN PASSENGER, AUTOMATICREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMEEC-IV CEC SYSTEMQUICK TESTTEST D9 - CONVERTER CLUTCH OVERRIDE (CCO) SHIFT SOLENOID 3/4-4/3 (SS 3/4-4/3)CODES 85 OR 86 DISPLAYED
1988 Ford Aerostar Van Passenger, Automatic
Codes 85 Or 86 Displayed
1988 Ford Aerostar Van Passenger, AutomaticSECTION Codes 85 Or 86 Displayed
- Checking SS 3/4-4/3 Resistance - Turn key off and wait 10 seconds. Set DVOM on 200-ohm scale. Disconnect SS 3/4-4/3 connector and measure solenoid resistance between SS and VPWR. If resistance is less than 26 ohms or more than 40 ohms, diagnose A4LD transmission. If resistance is between 26 and 40 ohms, go to next step.
- Checking Voltage to VPWR Circuit - Disconnect SS 3/4-4/3. With KOEO, set DVOM on 20-volt scale and measure voltage at SS 3/4-4/3 solenoid connector between VPWR circuit and ground. If reading is less than 10.5 volts, repair open circuit in harness and repeat QUICK TEST . If reading is 10.5 volts or more, go to next step.
- Checking Continuity of SS 3/4-4/3 Circuit - Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box, leaving ECA and shift solenoid disconnected. Set DVOM on 200-ohm scale. Measure resistance between Test Pin No. 42 and shift solenoid circuit at solenoid harness connector. If reading is 5 ohms or more, repair open in harness. Repeat QUICK TEST . If reading is less than 5 ohms, go to next step.
- Checking Circuit For Short to Ground - Turn key off and wait 10 seconds. Leave breakout box installed and ECA disconnected. Disconnect shift solenoid. Set DVOM on 200K-ohm scale. Measure resistance between Test Pin No. 42 and Test Pins No. 40, 46, and 60 at breakout box. If any reading is less than 10K ohms, repair short to ground and repeat QUICK TEST . If all readings are 10K ohms or more, go to next step.
- Checking SS 3/4-4/3 Circuit For Short to Power - Turn key off and wait 10 seconds. Leave breakout box installed, ECA and shift solenoid disconnected. Set DVOM on 200K-ohm scale. Measure resistance between Test Pin No. 42 and Test Pins No. 37 and 57 at breakout box. If all readings are 10K ohms or more, replace ECA and repeat QUICK TEST . If any reading is less than 10K ohms, repair short to power and repeat QUICK TEST. If code is repeated, replace ECA.
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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.