Cold engine oil is quite viscous. This leads to high oil pressure, which causes the control lamp to go out when starting the engine or immediately after. In a warm engine in hot summer, the oil is thinner, and with correspondingly low pressure, the control lamp goes out only at high engine speeds.
Troubleshooting
If the oil pressure warning light suddenly comes on while driving, it is always a warning sign:
If it lights up briefly during sudden braking or when turning quickly, the oil level has dropped below the minimum mark - check the oil level; if necessary, top it up.
If the light is constantly on, you should stop immediately.
Check the oil level.
If everything is OK, the next step is to check if there is a short circuit in the wire from the oil pressure switch to the warning light: turn on the ignition, disconnect the wire connector on the oil pressure switch.
The light should go out when the engine is not running; it is best for the assistant to observe this.
But if it continues to burn, then somewhere the wire has worn through and is in contact with the ground. This does not matter for the engine, and you can continue driving.
Typically, when the oil pressure light comes on, it means that the engine's lubrication points are not getting the proper oil pressure.
In most cases, the reason for this is not a defect in the oil pump, but much more often in the jamming of the pressure control valve (see chapter on engine).
It is also possible that a sudden oil leak could occur due to a loose oil drain plug that was not tightened properly.
If a defect is found that poses a danger to the engine, do not continue driving under any circumstances. The Vectra must be towed.
If the oil pressure warning light keeps flashing, it is often a faulty oil pressure switch. The only way to check this properly is to replace the switch.
Temporary road test: Move the oil pressure switch connector tab back and forth. Does the light go out now if the engine was started briefly?
Oil pressure light does not come on when you turn the ignition key? Turn the ignition on, disconnect the plug connector on the oil pressure switch and apply it to bare metal.
If the warning light now lights up, the problem is in the oil pressure switch. Replace the switch.
If the bulb does not light, then the defect is in the current-supplying wire or in the incandescent bulb itself.
The oil pressure switch (arrow) on the right side of the engine, via the oil pressure indicator light in the instrument panel, signals whether there is sufficient oil pressure in the engine bearings.
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