Test Point 1 - Sensor Circuit (Ohmmeter)
Test Point 1 - SENSOR CIRCUIT (Ohmmeter)1. Total Sensor Circuit
The entire sensor circuit can be checked for breaks on the control unit operating motor after removing the footwell shelf on the driver's side.
Testing
Pull off 12-pin plug on the control unit operating motor.
Connect ohmmeter (range: x 100) on plug terminals 4 (yellow) and 12 (yellow).
Ohmmeter should display some resistance. Move temperature switch from 18° to 30° to 18°.
The displayed resistance value must change (approx. 1000 ohms). No change in test value - see section 1.4.
If ohmmeter shows infinite ohms, there is a break in the sensor circuit.
Note: Breaks could be on wire connections in plug, on plug connections, on inside or outside sensor and on the control switch.
1.2 Outside Sensor
The outside temperature sensor is located front left in the alternator's cooling air hose.
Electric connection is made with a 2-pin plug in the left headlight housing and a 4-pin flat male plug behind the right center console trim panel.
Testing
Remove trim panel on right side of center console.
Disconnect 4-pin plug (term. 3/4 both with yellow wire).
Connect ohmmeter (range: x 10) on term. 3 (yellow) and 4 (yellow) on socket end of plug.
Ohmmeter should display following values:
approx. 933 ohms at 0 °C
approx. 588 ohms at 20 °C
approx. 457 ohms at 30 °C
Important: To change the resistance, the cooling air hose can be disconnected on the alternator and air blown into the hose with a hot air blower - the displayed value must drop.
Repeat tests on the sensor itself (plug in headlight housing), if test values are not reached.
(Possibly high resistance, loose wires, etc.)
Display of infinite ohms indicates a break.
Note: If the sensor wire has a break, the system will be regulated in heating direction and can no longer be regulated with the temperature switch (18 - 30 °C).
If the sensor has a short, the system will be regulated in warm direction, but only half of the control distance.
1.3 Inside Sensor
The inside temperature sensor is located in the sensor housing (to the right of the center nozzle) in the draft of a small blower. The electric connection is made with a 4-pin flat male plug behind the right center console trim panel.
Testing
Remove trim panel on right side of center console.
Disconnect 4-pin flat male plug (term. 1/2 both with yellow wire).
Connect ohmmeter (range: x 100) on plug pins of term. 1 and 2 (both yellow).
Ohmmeter must display the following values.
approx. 2570 ohms at 20 °C
approx. 2220 ohms at 25 °C
approx. 1900 ohms at 30 °C
Important: The test value measured in the sensor housing must drop by heating up the sensor resistor with a hot air blower. Replace the sensor, if there is not display or no change in resistance. Repeat this test before installing a new sensor.
Blower Test
Connect plug.
Turn on ignition. Set program switch optionally to
The sensor blower must be running!
Place a small piece of paper on the inlet opening or, if you smoke and smoking is permitted, blow cigarette smoke against the intake opening.
If the paper is not held or the smoke not drawn in, check whether blower is running or wire has a break or power supply is missing.
Note: If the sensor wire has a break, the system will be regulated in heating direction and it can no longer be regulated with the temperature switch (18 - 30 °C).
If the sensor has a short, the system will be regulated in cold direction (not in 30° position).
If the sensor blower does not run, even only sometimes, there will be very sluggish temperature regulation in the passenger compartment.
1.4 Temperature Adjusting Potentiometer in Control Switch
A potentiometer, which is adjusted by the temperature switch, is installed in the control switch.
a) Test
Remove trim panel on right side of center console.
Disconnect 4-pin plug of inside sensor. Connect ohmmeter (range: x 10) on socket end term. 1 (yellow).
Temp. lever at 18 °C = approx. 760 ± 100 ohms
Temp. lever at 30 °C = approx. 1760 ± 100 ohms
It is important, that the resistance value changes by approx. 1000 ohms each time.
Remove control switch, if values are not reached or there is no change in resistance between 18 °C - 30 °C - 18°C.
b) Test
Connect ohmmeter on platinum paths 13 and 14 of the platinum connection. Repeat test described above.
No display - replace control switch.
Display - break in wire.
1.5 Control Unit - Operating Motor
See nominal functions in point A.
It is recommended to connect a new part for comparison, if there is no function and the sensor circuit (test points 1.1 to 1.4) is okay. If the operating motor crank moves as described in point A or if the crank moves when changing the temperature of the inside or outside sensor (control switch/temperature switch in position A), it can be assumed that the installed operating motor is faulty.