Larry_G_928

Good Morning.

The coolant light on my '87 S-4 comes on and will not go off. The coolant level is normal and the cooling system appears to be working normally. This warning light comes on when either the coolant level switch or the coolant pressure switch sets the warning in the central warning computer. Here is what I have done so far:

1. Cleaned connections to both the pressure switch and the coolant level switch, restarted the car, light is still on.

2. Disconnected the battery, jumpered the coolant level switch, reconnected the battery, and started the car, light is still on.

3. Disconnected the battery, jumpered the pressure switch, reconnected the battery, and started the car, light is still on.

4. Disconnected the battery, jumpered BOTH switches, reconnected the battery, and started the car, light is still on.

5. With both switches jumpered, drove around for a few minutes, restarted the car several times, light is still on.

Any suggestions?

Larry Gunter
Fredericksburg, VA

Lizard928

dont know the system 100%, but is there a relay

Larry_G_928

There is a fuse for the instrument warning lights, however, the light wouldn't be on if this fuse were out. If there is a relay, does anybody know what it is?

Larry_G_928

How can the pressure switch be tested? If it is stuck closed how can that be determined?

Porsche930

The very problem happened to me as well in my 88 S4. The coolant level in the expansion tank looked adequate. However believe it or not, I just simply added a cup or a little more coolant to the tank, the light shutted off ever since. Hope yours is as simple as mine. Good luck.
Tony
88 S4 auto

Larry_G_928

Tried that already. The way the switch works (I think) is when the float level reaches a certain point the circuit is completed and the light goes out. Jumpering the switch does the same thing. The coolant level is normal.

I just checked for a reading and ground at the connectors. It looks normal.

Larry_G_928

Okay I just jumpered the level switch with the pressure switch disconnected since jumpering the pressure switch will trigger the warning light...the light STILL stays on! I have a reading at the connectors. This problem is truly baffling me!

T_MaX

These two switches are wired together and like BerNard94 said, they are N/O (Normaly Open)!

Pull all jumpers off and do not reconnect the wires! Now try it and see if the light is off.

They are simple on and off switches, If the float in the coolant tank is at the top and you have continuity between the two poles, it time to replace it.

If you have continuity between the two poles of the of the PSI switch when the car is cold or removed from the car, it needs replacement.

Erik - Denmark

Larry,
Most properly that's your pressure sensor, the way it works is a little tricky, see the attached copy of Porsche's service manual from 1984
http://forums.rennlist.com/upload/pr...ensor_copy.jpg
Good luck with your 'study'
Regards from Erik in Denmark