Outside Temperature Display: Testing and Inspection

Testing electrical outside temperature display

Preceding work:
Instrument cluster removed. Service and Repair


A. Test

Up To 08/87:

As Of 09/87:

- Test voltage at 5-pin coupling of outside temperature display (A1p4) between contact 5 (terminal 15) and contact 1 (ground).
Key in position "2". Specification: battery voltage.

- Test lighting at 5-pin coupling for outside temperature display (A1p4) between contact 1 (ground) and contact 2 (instrument lighting). Lighting switched on. The voltage measured is dependent on the position of the rheostat (A1r1) of the instrument lighting.
- If the specifications are not achieved, check contacts and wiring for open circuit.
Main ground behind instrument cluster (W1), fuse and relay box (F1) and terminal block, terminal 58d (X6) to plug connection, outside temperature display.
- Test temperature sensor, outside temperature display (B14).



- Test outside temperature display (A1p4). Feed in resistances with ohms decade at 2-pin coupling.




Note: Measuring range -38 °C to +58 °C (Readout at intervals of 0.5 °C).


B. Function

- Up to 08/87, the outside temperature display is supplied direct by the temperature sensor.
- As of 09/87, the outside temperature display analyzes the road speed signal from the Hall sensor.
- When the engine is started, the temperature measured is displayed. The memory is activated if, after starting the engine, the vehicle has been driven no faster than 20 km/h.
- As the temperature drops, the readout always appears immediately no matter the speed.
- At speeds below approx. 20 km/h the temperature last measured is stored and displayed.
- If the temperature rises, the stored temperature is displayed in order to avoid any incorrect measurement. This prevents an incorrect temperature being displayed when driving slowly or when the car is stopped and the temperature sensor is heated up e.g. as a result of exhaust gases from the vehicle in front or from heat radiated by the radiator.
- At speeds between approx. 20-60 km/h the temperature displayed changes after about 5 minutes in line with the temperature measured. The change in the readout is open from approx. 60 km/h.

Note: Only display units with 5-pin connector (with road speed signal) are stocked as replacement parts. If these display instruments are installed in vehicles manufactured up to an including model year 1987, the coupling at the connection cable should also be replaced by the coupling supplied.

Special Tools:

Commercially Available Tester: