my bosch 800 series dishwasher just shows three dashes "---" on the display and won't start, what's wrong?

Diagnosis

The appearance of three dashes "---" on the display of the Bosch 800 Series SHPM88Z75N is a specific communication error indicating that the control module is not receiving a "closed" signal from the door latch assembly. This is a critical safety interlock; the dishwasher will not engage the pump or heat the water if it believes the door is open, as this would cause flooding and steam burns. This issue typically occurs because of a mechanical misalignment where the door strike plate isn't fully engaging the latch, or an electrical failure within the microswitch. Over time, detergent residue or hard water deposits can build up inside the latch mechanism, preventing the spring-loaded switch from fully depressing. In more severe cases, the internal copper contacts of the microswitch have worn down or oxidized, breaking the electrical circuit even when the door is physically shut. You can confirm this by attempting to push the door firmly against the chassis; if the dashes flicker or disappear momentarily, the issue is mechanical alignment. If the display remains static regardless of pressure, the switch has likely failed electrically.

How to Fix It

To resolve this, you must first attempt a hard reset to clear the control board's temporary memory, followed by a physical inspection and potential replacement of the latch.

1. Locate your home's electrical panel and flip the circuit breaker dedicated to the dishwasher to the "OFF" position. Leave the power disconnected for exactly three minutes to allow the capacitors on the control board to discharge completely.
2. Restore power. If the "---" persists, open the door and inspect the strike plate (the hook-like piece on the top of the door). Ensure there is no debris or buildup of soap scum preventing the door from seating flush against the tub.
3. Remove the inner door panel. This requires removing the screws from the bottom and side edges of the door liner. Carefully peel back the liner to expose the door latch assembly.
4. Locate the microswitch on the latch assembly. Use a multimeter set to the continuity setting (ohms). Place the probes on the switch terminals; if the switch does not show a change in continuity when you manually depress the lever, the switch is dead.
5. Replace the door latch assembly. For the SHPM88Z75N, you will need the latch assembly (typically part number 00611913 or the updated equivalent). Unscrew the old assembly from the chassis, disconnect the wiring harness, and snap the new assembly into place.
6. Reassemble the door liner and test the unit by starting a "Quick" cycle to ensure the "---" error is gone.

If That Didn't Work

• Inspect the wiring harness leading from the door to the main control board. Look for "rub-through" points where the wires may have frayed due to the repeated opening and closing of the door. If you find a pinched wire, strip the insulation, solder the connection, and seal it with heat-shrink tubing.
• Check the door hinges for sagging. If the door has dropped even 2-3 millimeters, the strike plate will miss the center of the latch, triggering the "---" error. Adjust the hinge tension or replace the hinge pins to ensure the door closes perfectly square.
• Perform a "Control Module Reset." While the door is open, press and hold the "Start" button for 5 seconds, then press the "Power" button. This can sometimes force the board to re-poll the door sensor.
• Inspect the main control board for burnt capacitors or "cold" solder joints. If the latch is working but the board isn't receiving the signal, the issue is on the PCB. Look for a small brown scorch mark near the door-sensor input pins on the main board.

Heads Up

• Avoid using "heavy-duty" or "extra-strength" detergent pods in excess, as the caustic residue can leak into the door seal and corrode the microswitch contacts over time.
• Never force the door shut if you feel resistance; this can bend the strike plate, leading to intermittent "---" errors that are difficult to diagnose.
• When replacing the latch, ensure the wiring harness "clicks" firmly into place; a loose connection here will mimic a failed switch and bring the error back immediately.
• Periodically wipe down the top edge of the door and the latch area with a damp microfiber cloth to prevent mineral buildup from interfering with the mechanical closure.