What does it mean?
B1958 is a Body (airbags, seat belts, body electronics) fault code. It indicates: Rear MICU Lost Communication with Combination Switch Control Unit (WIPSW Message) .
Symptoms
- Wipers do not respond to the stalk, or only run in one speed
- Intermittent wipe delay settings ignored
- Wipers switch on by themselves or keep running after the stalk is switched off
- Rear wiper or washer inoperative on vehicles where the rear unit drives them
- Other stalk functions affected and further communication codes stored
Likely causes
- Broken or shorted multiplex wire between the column switch unit and the rear control unit
- Corroded or loose connector at the column switch assembly
- Fuse failure or an open supply wire leaving the column switch unit without power
- Water reaching the column or the cowl area and corroding terminals
- Internal fault in the wiper switch section of the combination switch control unit
- Poor ground shared by the column switch unit and other body modules
- Damaged rear control unit or corrosion inside it
How to fix it
- Operate the wiper stalk through every position and note exactly which functions are lost
- Scan all modules and compare the reported lost communication entries to find the common unit
- Check the fuse and supply for the combination switch control unit, then verify its ground with a voltage drop test
- Watch the wiper switch input in live data, if it never changes the message really is missing rather than the wiper motor being at fault
- With both units disconnected, check the message wire for continuity and for shorts, moving the harness at the bulkhead grommet
- Clean and reseat the column connectors, repairing any corroded terminals
- Repair the circuit and retest before replacing the combination switch control unit or the rear control unit