Owner's Problem Description
The owner of a 1996 Ford Escort with a 1.9L engine (no A/C) reports that the cooling fan turns on immediately after starting the engine and remains on until the engine is turned off. It does not activate when the key is turned on, only after the engine starts. The engine operates within normal temperature ranges, and the owner has checked the relays and wiring for corrosion without finding any issues. They've observed similar behavior in other Ford vehicles and are questioning whether it could be a faulty relay or a ground issue related to the computer.
Professional Technical Analysis
This 1996 Ford Escort, equipped with a 1.9L engine and no air conditioning, has been reported to have its cooling fan running continuously after the engine is started. This symptom is particularly interesting as the fan should typically be controlled by a temperature sensor or the PCM (Powertrain Control Module). The vehicle has been inspected for common issues such as faulty relays or corroded wiring, but no obvious faults were found. The fact that the fan operates only after the engine starts, and not when the key is turned on, suggests that the issue may lie within the fan control circuit rather than the fan or its relay itself. The high-side fan activation could indicate a malfunction of the temperature sensor or a short circuit causing the fan to receive an incorrect signal. Given the owner's observation of similar occurrences in other Ford models, it is worthwhile to consider the possibility of a design flaw or common failure point in the Ford cooling systems of that era. Safety-wise, while the engine is not overheating, leaving the fan on continuously could lead to premature wear on the fan motor and electrical components. A systematic diagnostic approach using an OBD-II scanner to check for any related fault codes, along with inspecting the wiring diagrams to trace the fan control circuit, would be prudent steps to take. Additionally, assessing the voltage levels at the fan relay and testing the temperature sensor's resistance under varying temperatures could provide further insight into the underlying issue.
Possible Causes
Most common causes (ordered by frequency):
- Faulty Cooling Fan Relay: The relay controlling the cooling fan may have a stuck contact or internal failure, causing the fan to receive a constant power signal once the engine is running. Checking the relay with a multimeter for continuity and testing the relay operation under load conditions is essential. The relay should have an OEM part number of F67Z-8C607-A. A new relay typically costs around $30-$50. - Constant operation of the cooling fan upon engine start, audible relay clicking when testing.
- Temperature Sensor Malfunction: The temperature sensor may be providing incorrect readings to the PCM, leading to a false signal that activates the fan continuously. Testing the sensor's resistance at various temperatures can help diagnose this issue. The typical resistance should be around 2.5k ohms at 20°C and decrease as the temperature rises. The part number for the OEM sensor is F7DZ-12A648-AB, costing approximately $40-$60. - Inconsistent fan operation based on engine temperature, potential stored codes related to temperature sensor.
- Wiring Issues: Corroded or damaged wiring in the fan control circuit could be causing the fan to operate continuously. Inspecting the wiring harness for visible damage and ensuring solid ground connections will be necessary. A continuity test should reveal any breaks or high-resistance areas in the wiring. Repairing or replacing damaged wiring could cost around $50-$150 depending on the location and extent of damage. - Visual inspection reveals wear on wiring insulation, intermittent connectivity issues when testing.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - Initial Diagnostic Scan: Begin with a comprehensive OBD-II scan using a professional scanner or GeekOBD APP to check for any stored fault codes related to the cooling system. Look for codes specific to the temperature sensor or fan relay malfunctions. This helps to identify any electronic issues that might be contributing to fan operation.
- STEP 2 - Physical Inspection: Conduct a physical inspection of the cooling fan relay, wiring harness, and temperature sensor connections. Check for corrosion, loose connections, or damaged wires. Ensure that the ground connections are solid. This step could reveal visible issues that may not show up in electronic diagnostics.
- STEP 3 - Relay Testing: Test the cooling fan relay by applying voltage directly to the relay terminals to see if the fan operates as expected. Use a multimeter to check for continuity and resistance. A good relay should show continuity and operate without overheating. If it fails these tests, replacement is necessary.
- STEP 4 - Temperature Sensor Verification: Verify the temperature sensor readings by measuring its resistance at varying temperatures. Compare the readings to the expected values. If the readings are outside the normal range, replacement may be required. Use the GeekOBD APP to monitor live data and confirm the sensor's operation while the engine is running.
