What is the reason for the tachometer not returning to zero?
2 Answers
The reasons for the tachometer not returning to zero are: 1. The speedometer in the vehicle's instrument cluster malfunctions, causing the tachometer needle to stop moving; 2. The vehicle's mileage sensor fails. Check if the flexible shaft connection is disconnected, then observe whether the mileage starts to increase. If only the tachometer stops working, it needs to be replaced with a new one; 3. There is a foreign object stuck inside the instrument, preventing movement. Open the instrument to remove the foreign object. The tachometer is usually located within the instrument panel, placed symmetrically with the speedometer and odometer. It operates based on magnetic principles, receiving pulse signals generated when the primary current in the ignition coil is interrupted, and converting these signals into displayable RPM values. The faster the engine speed, the more pulses the ignition coil generates, resulting in a higher RPM value displayed on the gauge.
That day my car was parked in the garage, and after I turned off the engine, the tachometer needle was stuck at 500 RPM and wouldn't move. This condition is usually caused by issues in three areas: dust in the speed sensor connector leading to poor contact, a short circuit in the dashboard's internal circuit board due to moisture, or data corruption in the engine control unit. My neighbor's old Bora had the same issue—disconnecting the battery for ten minutes and reconnecting it made the needle obediently return to zero. If this trick doesn't work, I recommend using a diagnostic tool to read the trouble codes, focusing on the speed signal wiring—there might be a mouse that chewed through the insulation. If you encounter this situation, don't force the car to run; if the dashboard completely fails and you can't even see the speed, it could be dangerous.
