Instruments - Coolant Light is ON, Switch Testing

Group 17
Radiator

Bulletin Number
17 02 96

Woodcliff Lake, NJ
May 1996
Product Engineering

SUBJECT:
Coolant level switch, part number 61 31 1 384 739

MODELS:
E34 with M50 and M20 engines
E36 with M50, S50 and M52 (up to May 96 production) engines

Situation:

A substantial number of coolant level switches are being replaced under warranty. The most frequent dealer comment is "coolant light is on, replaced coolant level switch". A detailed investigation of the replaced parts showed that more than 60% of them were non-defective.

Action:

It is necessary to ensure that the cause for the complaint "coolant light is on" is due to a defective coolant level switch before replacing it.

Procedure:

When a vehicle is brought in with the complaint "coolant light is on", use the following method to identify a defective coolant level switch:

1. Open the cap of the radiator/expansion tank and locate the coolant level switch mounted in the bottom. Use an appropriate piece of wire to slide the float up and down. Ensure that the float moves easily and stays in the up position by itself while the coolant level is correct. If the float sinks in the coolant, the coolant level switch has to be replaced.

2. Disconnect the cable connector on the coolant level switch and connect an ohmmeter to the both contact pins of the installed coolant level switch. Measure the ohmic resistance of the coolant level switch in both float positions. The following resistance values indicate a defective coolant level switch, that has to be replaced:

float up: resistance more than 1 ohm
float down: resistance less than 40 k/ohm

3. If the coolant level switch shows correct resistance values in both float positions, check the cable connector for corrosion or soiling. Ensure proper electrical contact and connect the cable connector again.

4. With the ignition on, slide the float down until it stops and hold it in this position. Wait at least 20 seconds and turn the ignition off. A coolant level warning should be displayed in the instrument cluster/information display.

Let the float slide back to the up position. Turn the ignition on, wait at least 20 seconds and turn the ignition off again. The instrument cluster/information display should not show a coolant level warning.