Engine Temp Sensor Diagnostics

[wake74]

1995 318ti, with M42 engine.  I can't get water temperature gauge in car to work.  When key is moved to on position, it moves about 1/2 a needle to the full cold line.  I have pulled intake to access sensor.  New sensor, in boiling water, no change.  When I remove the sensor, and loop a wire between the two terminals on the socket, no change (should go full hot I think).  When I put the dash into diagnostic mode (hold dash button, turn key to start), the temp gauge will cycle all the way to hot at the same time as the rest of the gauges.  Rest of the gauges are fine during normal operation.

I'm not even sure where to go from here.  I don't know of any other wire junctions to check.

Thoughts?

Thanks!

Glenn

[DesktopDave]

Test the sensor's resistance with a digital multimeter or ohmmeter.  You should see high resistance when it's cool (like 3K ohms) and low resistance as it warms up (like 300 ohms).

[wake74]

Thanks.

I can check that but if I short the connector at the sender it should make the gauge go full hot. That is the part that has me stumped.

Any other thoughts?


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[colin86325]

The temp gauge sender has only one terminal (pole), so it sounds like you have the engine temp sensor and the gauge sender mixed up.  Pretty common actually.

[wake74]

At least on my E36 M42 both connectors (DME and gauge) are two conductors. The grounds go back to the dash or DME.   I think the older E30s grounded to the block.

I am actually wondering now if the temp gauge doesn't work without the car running. The gauge is apparently heavily dampened by the DME.

Anyone know if the temp gauge is supposed to function without the car running. on a '95 318ti?

Thanks for the continues suggestions!




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[colin86325]

My apologies, I just assumed you had an E30!  Hope you get it sorted.

[DesktopDave]

At least on my E36 M42 both connectors (DME and gauge) are two conductors. The grounds go back to the dash or DME.   I think the older E30s grounded to the block.

I am actually wondering now if the temp gauge doesn't work without the car running. The gauge is apparently heavily dampened by the DME.

Anyone know if the temp gauge is supposed to function without the car running. on a '95 318ti?

The E30 and early E36 systems are the same, with detail differences.  The E30 gauge sender does only have one connector wire, and is grounded to the block.  It's usually a blue body and/or connector mounted further forward in the head.  Make sure you have the right part number on that sender too - those two coolant senders are different part numbers and are not 100% compatible.  The E30s all have one pin on both the sender and the harness.

You have an oddball hybrid, but a Ti is more E30 than E36.  That cluster is unique to your car.  IMHO I'd suspect it's just an updated E30 cluster.  I'd be temped to check the gauge pins going through the board, or caps on the SI board.  They can die from temperature, age or just an unlucky overload.

The temp gauge won't report the temperature without power - the needle is powered by 12vdc to a small coil; the SI board should read sensor resistance (or indirectly shunt voltage) to determine output to the gauge's coil.  Don't short the connector to test a sensor - it's possible to damage the driver board that way.  I'd strongly recommend using only BMW's ETM (or Bosch's specs) to run tests - some items can't be tested directly without an oscilloscope and/or other exotic equipment.

Other E36 have a gauge test mode, but I don't think the Compact cluster can do that.  To test those, push the odo reset button in, insert the key and turn it to Position 1 (Accessory Power).

[Bald Eagle]

Had similar issue after Maint. Hooked up wires wrong. See this post for correct sensor wires:

http://www.m42club.com/forum/index.php?topic=2742.msg121435#msg121435

[wake74]

I guess I forgot to follow up on this forum and close out the thread. The issue turned out to be something faulty within the cluster. I swapped the cluster and now have the correct temp gauge readings. Thanks!