Speedometer not working, and cruise control too?
A speedometer that reads wrong is not always a problem with the gauge itself. The gauge shares its speed information with other systems, so your cruise control can stop working at the same time.
Maybe your needle jumps. Maybe the digital speed does not match your real speed, or the gauge has stopped responding at all. Any of those is worth testing rather than living with. Here is what can cause it, and why one fault can show up in three places at once.
What makes a speedometer read wrong?
Your speedometer is one of those parts you don't think about until it starts acting up. It also does more than show how fast you are driving. It works with several systems: the wheel speed sensors, the transmission, the instrument cluster, and the vehicle's computer. When one of those parts sends the wrong information, the speedometer can display an incorrect speed or stop working entirely.
Our page on speedometer repair in Campbell lists the causes, and which one it is depends on the vehicle:
- A faulty speed sensor
- Damaged wiring
- A cluster issue
- A computer communication problem
- A transmission-related concern
Only one of those five is the gauge. That is the useful part. Because the speedometer is connected to other systems, the problem may not be limited to the gauge at all. That is why proper testing matters.
Why did my cruise control stop working too?
Cruise control trouble is one of the signs of a speedometer problem, because the speedometer works together with the same vehicle systems. The other common signs are a bouncing needle and a digital speed reading that does not match your actual speed. On some vehicles, transmission shifting problems show up too.
So two or three symptoms at once do not have to mean two or three failures. They can mean one piece of wrong speed information reaching several systems. That is worth knowing before anyone starts replacing parts.
Can wiring, the battery, or the alternator cause this?
All three are worth checking. Damaged wiring is one of the five causes above. Wiring faults come from electric shorts and opens, damaged control modules, cuts to and broken wiring, and other causes. Other signs that point at wiring include lights that are dim or flickering, fuses that blow, and a burning smell. Electrical faults are some of the hardest to diagnose, because almost everything in a vehicle runs off electrical now.
Not all of it shows up on a screen. On electrical and wiring problems we use all five senses, not just a tool. We can feel a fluid leaking onto an electrical connector. We can see where rodents have been chewing on the soy-based coatings that surround vehicle wiring.
The charging system is worth a look as well. An erratic speedometer is one of the early warning signs of a failing alternator. So are dimming or flickering lights, an unusual whining or grinding noise, the battery warning light, and slow cranking. We covered those signs in our post on why a car battery dies so quickly. The point is the same either way: the symptom you notice first does not tell you where the fault is.
Is it safe to drive with a broken speedometer?
An inaccurate speedometer affects your confidence behind the wheel, and it means you may not know how fast you are really going. That can lead to safety concerns, or even a speeding ticket. A working speedometer helps you drive safely, follow posted speed limits, and keep track of mileage-related maintenance.
What we do before replacing a part
We do not believe in guessing. Our technicians use professional computer diagnostics and a careful inspection process to work out where the problem is coming from. Then we inspect the system, explain what we find, and go through your repair options with you.
Our technicians stay current with modern vehicle technology, so we diagnose both older mechanical systems and newer computer-controlled vehicles. Qualifying repairs carry a 36 month / 36,000 mile limited warranty. The full terms and the exclusions are on our warranty page.
Autotrend Auto Repair, 2885 S Winchester Blvd, Suite F, Campbell, CA 95008, serving Campbell, West San Jose, Los Gatos, Saratoga, Cupertino and Cambrian Park. We are open Monday to Friday, 8:00 AM to 5:00 PM.
Call Autotrend Auto Repair at (408) 866-5140 to book a speedometer diagnosis.
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