Jaguar XJS Oil Pressure Switch: Common Problems and the Usual Causes
The oil pressure switch is like a fire alarm in your house. Just as the fire alarm sounds off when it senses smoke, the oil pressure switch turns on the warning light of your dashboard when the oil pressure is low. This will let you avoid a possibly catastrophic engine failure. You may get false warnings once in a while, but it's forgivable, given its very important job. When the false alarms become much more frequent, you'll need to have the unit checked right away. Here's how you can diagnose such problems associated with the Jaguar XJS oil pressure switch:
Oil pressure warning light switches on and off
When the oil pressure warning light first switches on, the first thing you must always do is to check the oil level of the Jaguar. If the reading on the Jaguar's dipstick shows that the oil level is between the minimum and maximum level, then you should check the oil pressure switch next. Disconnect the oil switch and check the oil gauge. If the warning light disappears, then it means that your oil switch is bad and needs to be replaced. If warning light is still on, there might be a problem with the electrical circuit of the oil pressure warning light.
Oil pressure light switches on when idle
If the XJS is idling, it is natural for the oil pressure in the engine to be low. Oil pressure switches are supposed to take that into account and prevent themselves from switching on the warning lights during idling. As always, once the light comes on, be sure to check the oil pressure of your Jaguar first. If the oil level is okay, try testing the switch with an ohmmeter. Test the switch with the Jaguar's engine off and do it again with the engine on; record both readings. The difference of both readings should be at least 500 ohms; any less means that there is a problem with the oil switch.
Other troubleshooting tips
Always assume the worse. When your oil warning light switches on, always assume that both your oil pressure and oil level is low. Check the oil level first before you try troubleshooting the oil pressure switch.