* Faulty Oil Pressure Sending Unit: This is the most common culprit. The sending unit measures oil pressure and sends a signal to the oil pressure gauge *and* the oil pressure warning light. The gauge might be getting a weak or intermittent signal, displaying seemingly acceptable pressure, while the light is triggered by a lower threshold or a different signal interpretation. The sending unit itself could be failing, giving incorrect readings to both the gauge and the light.
* Wiring Issues: A break, short, or poor connection in the wiring between the sending unit and either the gauge or the light could also cause this discrepancy. A bad ground connection is another possibility.
* Oil Pressure Gauge Inaccuracy: While less likely if the gauge is showing a reasonable reading, it's possible the gauge itself is faulty and not accurately reflecting the actual oil pressure. It's more probable that the gauge is only partially malfunctioning and is only reporting some of the fluctuation, while the warning light is reading the true condition.
* Low Oil Level (despite good pressure): While you mention good pressure, it's still possible to have enough oil for a *momentary* reading of pressure, but not enough for sustained lubrication. Check your oil level using the dipstick to rule this out. It's not as common a cause in this situation, but it is possible that the pump is just barely able to build up enough pressure for a short period.
Troubleshooting Steps:
1. Check the oil level: This is the first thing you should always do. Low oil, even with some pressure momentarily, is dangerous.
2. Inspect the oil pressure sending unit: Look for any obvious damage or corrosion.
3. Check the wiring: Carefully inspect the wiring harness connected to the sending unit for any breaks, chafing, or corrosion. Pay close attention to the ground wire.
4. Test the oil pressure sending unit: This requires a mechanical oil pressure gauge to accurately measure the oil pressure. You can borrow or rent one, or have a mechanic do it. Compare the mechanical gauge reading to the dash gauge. A significant difference indicates a faulty sending unit.
5. Replace the oil pressure sending unit: This is often the most cost-effective solution and is the most likely culprit. They are relatively inexpensive and easy to replace.
Important Note: Driving with the oil light on, regardless of the gauge reading, is risky. Continuing to drive could cause serious engine damage. It's best to address this issue immediately. If you're not comfortable performing these checks yourself, take your Ranger to a qualified mechanic.
