Checking the wiring and connections

Check the brake light switch and control unit connectors for contact resistance and oxidation as described in Contact resistance and oxidation .

Check the wire between brake light switch #1 and the battery for an intermittent open circuit as described in Open-circuit, intermittent faults .

Check the wire between brake light switch #2 and ABS control unit #23 for an intermittent open circuit as described in Open-circuit, intermittent faults , an intermittent short circuit to ground as described in Short-circuit to ground, intermittent faults , and for an intermittent short circuit to voltage supply as described in Short-circuit to supply voltage, intermittent faults .

Also check the wire between brake light switch #2 and engine control module (ECM) #B26 and central electronic module (CEM) #B4 for an intermittent short circuit to ground as described in Short-circuit to ground, intermittent faults , and an intermittent short circuit to voltage supply as described in Short-circuit to supply voltage, intermittent faults .

Do the necessary corrective action.

Additional information:

To connect the test box to the ABS control unit, see Connecting the breakout box .
To connect the test box to the central electronic module (CEM), see Connecting the breakout box .
To connect the test box to the engine control module (ECM), see Connecting the breakout box

Fig 1: Identifying Ohm Meter

Courtesy of VOLVO CARS OF NORTH AMERICA.

Fig 2: Identifying Brake (Stop) Light Switch

Courtesy of VOLVO CARS OF NORTH AMERICA.