In almost all cases, when a speedometer is not working, but the odometer is, the speedometer itself has failed. If the speedometer cable or VSS (vehicle speed sensor) had failed, the odometer would not turn.
How to Tell if a Speedometer is Bad
If you’re suspecting issues with your speedometer, it’s essential to identify the symptoms accurately.
A malfunctioning speedometer can range from being slightly annoying to significantly hazardous. Here are key signs to watch out for that indicate your speedometer might be bad:
- Inaccurate Readings: If your speedometer shows speeds that are obviously incorrect (e.g., reading too high or too low compared to your actual speed), it’s a clear sign of malfunction.
- Erratic Movement: A speedometer that jumps around or fluctuates rapidly without corresponding changes in speed indicates a problem.
- Stuck at Zero or Another Speed: If the speedometer needle doesn’t move from zero when you’re driving, or if it’s stuck at another speed regardless of your actual speed, there’s likely an issue.
- Check Engine Light: While the check engine light can indicate many different issues, combined with speedometer problems, it can point towards a malfunctioning vehicle speed sensor or related components.
- Cruise Control Failure: Since cruise control relies on speed sensor input, if your speedometer is malfunctioning, you might also experience problems with cruise control not engaging or working correctly.
- Transmission Shifting Issues: For vehicles with automatic transmissions, a faulty speed sensor (which can affect the speedometer) might lead to improper shifting behaviors.
To diagnose and address a faulty speedometer, consider the following steps:
- Check the Speed Sensor: Often, speedometer issues are due to a faulty speed sensor on the transmission. Inspect it for damage or disconnections.
- Inspect Wiring and Connectors: Look for damaged wires or loose connections that could be affecting the speedometer’s operation.
- Fuse Box Check: Ensure the fuse related to the instrument cluster or speedometer isn’t blown.
- Consult a Professional: For electronic speedometers, especially in modern vehicles, diagnostic equipment may be needed to read fault codes and accurately diagnose the issue.
Remember, driving with a malfunctioning speedometer isn’t just inconvenient—it can be unsafe and potentially illegal, as you might unknowingly exceed speed limits. If you’re not comfortable diagnosing or fixing the issue yourself, it’s wise to consult a professional mechanic.