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Checking the brake lights switch (TCS)

Checking the brake lights switch (TCS)


In order for the Cruise Control system to work, at least one of the brake light bulbs must be OK.

This means than pin G (7) of the Cruise Control connector must be grounded (through the brake light bulbs) before the Cruise Control system can be activated.


1. Check that the brake light bulbs are OK.

If they are not OK, change them and check again that they light up.

2. If the brake light bulbs are not OK, continue fault diagnosis as described in the section headed "ICE" in Service Manual 3:5 "Electrical system, instruments".

If the bulbs are OK, check the operation of the Cruise Control system.

3. If the Cruise Control system still does not work, check that about 12 V is present across pin G (7) of the Cruise Control connector and a good ground when the brake pedal is depressed.




4. If voltage is OK, continue fault diagnosis with .


If the voltage is not OK, connect an ISAT Scan Tool and go to the TCS system. Select "BRAKE LIGHT SWITCH" in the "OBTAIN READOUTS" menu. Check the operation of the Cruise Control system.

If it is OK, continue with point 5.

If it is not OK, proceed to point 6.

5. Select "DISENG CRUISE CONT" in the "OBTAIN READOUTS" menu of the Scan Tool and measure the voltage across pin G (7) and a good ground.


When "DISENG CRUISE CONT" is "ON", the voltage should be 12 V.

If voltage is OK, continue fault diagnosis with .

If the voltage is not OK, continue with point 6.

6. Check the wiring for continuity or a short circuit by measuring the resistance across pin 1 of the brake lights switch connector and pin 23 of the TCS control module connector.


If the resistance is > 1 ohm, rectify the fault.

If the resistance is > 1 ohm, continue with point 7.

7. Check the wiring for continuity or a short circuit by measuring the resistance across pin 5 of the TCS control module connector and pin G (7) of the Cruise Control connector.


If the resistance is > 1 ohm, rectify the fault.

If the resistance is > 1 ohm, continue fault diagnosis as described in Service Manual 2:7 "Traction Control System".