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HOMESERVICE MANUALSFORD1991AEROSTAR VAN CARGO EXTENDED, 4.0 X, AWDREPAIR AND DIAGNOSIS (SINGLE PAGE)TRANSMISSIONAUTOMATIC TRANSDIAGNOSIS - A4LDDESCRIPTION & OPERATION
1991 Ford Aerostar Van Cargo Extended, 4.0 X, AWD

Description & Operation

1991 Ford Aerostar Van Cargo Extended, 4.0 X, AWDSECTION Description & Operation

The center of the EEC-IV system is the Electronic Control Assembly (ECA). The ECA receives information from various sensors and switches. Based on information received, the ECA generates output signals to control engine and transmission operation. The EEC-IV system controls 3 major areas of engine operation: air/fuel mixture, ignition and emission control. In addition, the system controls A/C compressor clutch operation, idle speed, transmission converter clutch and 3-4 shift solenoids. The system has self-diagnostic capabilities.

The engine control system consists of the ECA, sensors, switches and solenoids. In order for the ECA to perform properly, it must be kept constantly informed of engine operating conditions. It is the task of the engine sensors to supply the ECA, via electrical signals, with specific information required to determine engine operating conditions. The ECA will then send out electrical signals to control air/fuel ratio, emission controls, idle speed, ignition timing, and transmission solenoids.

Perform all possible test steps under TROUBLE SHOOTING in the AUTO TRANS OVERHAUL - FORD A4LD article. If referred here by trouble shooting charts or testing procedure, proceed with self-diagnostics. CIRCUIT TEST TC under CIRCUIT TEST  may also be used to help bench test and diagnose solenoids. Transmission fault codes are only output in the KOEO Self-Test.

NOTE: Only 2 transmission fault codes are used for this transmission. Additional fault codes may be output during QUICK TEST procedure. These fault codes may pertain to engine performance and must be repaired first, as engine performance will greatly affect transmission operation. For information and testing procedures of engine related components, see appropriate TESTS W/CODES - EEC-IV article in the ENGINE PERFORMANCE section.
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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.