What Causes the Engine Tachometer to Stop Working?
2 Answers
Reasons why the engine tachometer stops working: 1. Disconnected flexible shaft; 2. Foreign object stuck inside the gauge; 3. Instrument panel malfunction; 4. Wiring issues; 5. Detached pointer. The tachometer is installed in the instrument panel, symmetrically placed alongside the speedometer. Most passenger cars feature electronic tachometers, which come in either analog (pointer) or digital (LCD) display formats. Working principle of the tachometer: It receives pulse signals generated when the primary current in the ignition coil is interrupted, converts this signal into a displayable RPM value. The faster the engine runs, the more pulses the ignition coil generates, resulting in a higher RPM reading on the gauge.
Last time I encountered a stuck tachometer, and after careful inspection, I found that the wiring harness connector behind the dashboard was loose. Apart from poor contact, it could also be due to a stuck needle or a burned-out stepper motor in the instrument cluster assembly. Another easily overlooked issue is a faulty vehicle speed sensor, which is related to the tachometer signal. Remember to check the corresponding 10A fuse in the fuse box—if it's blown, the tachometer won't work. If all other instruments are functioning normally, it's most likely an issue with the tachometer itself. You can open up the dashboard and use a multimeter to check the power supply on the circuit board. For older cars, it's advisable to inspect the dashboard circuit board for swollen capacitors—I've repaired three cars where capacitor leakage caused a short circuit.
