The dashboard lights in your car tell a complex story about everything from your current speed, to the health and condition of your engine, and even whether items like your headlights are on. Different vehicles have different measures and some dashboards are much more complicated than others. But when the sensors in your car stop working, you cannot ignore this situation.
When one sensor stops working, the problem may be the sensor itself, or a bad sensor, while all disabled sensors at the same time often indicate blown fuse or faulty instrument cluster.
The most common causes of malfunctioning sensors in a car can be broken down into three scenarios:
None of the sensors are working.
- If none of the sensors work at all, the problem could be a blown fuse or a faulty instrument cluster.
- If all gauges show low or erratic, it could be a problem with the voltage regulator that powers the instrument cluster.
- If all sensors are connected to the highest possible reading, it could be due to a wiring problem or a bad voltage regulator on the instrument.
The individual sensor does not work.
- If the oil, coolant, charge, or gas pressure gauge is not working or is malfunctioning, the problem is with the gauge, wiring, or sender.
- Speedometers are unique in that some use physical cables instead of sensors, so a speedometer not working can also indicate a broken cable or stripped gear.
One or more warning lights on the instrument panel are not working.
- If one or more warning lights do not come on when the key is first turned on, this usually indicates a burned out light bulb.
- If none of the lights come on, check the fuses and wiring to the instrument cluster first.
- If the check light comes on and stays on while the engine is running, this usually indicates a problem with that particular system.
The appliances in the car don’t work at all.
There are many different types structures and configurations combinations appliances but when all the sensors in a car stop working at once, it’s usually a fuse or wiring problem. The first step in diagnosing this type of problem is to identify the fuse associated with the instrument cluster or sensors.
The fuse must be energized on both sides when the ignition key is turned to the on position. You can check it with an inexpensive test light or multimeter or take your car to a mechanic if you don’t have the right tools or don’t like digging into such diagnostics.
If the fuse is good, the next thing you or your mechanic will want to do is check the power on the individual sensors. This usually requires removal of the instrument cluster, which can be quite difficult and time consuming in some vehicles.
At a minimum, you will probably have to remove some of the trim and unscrew the cluster to free it. The level of difficulty is usually on the same level as installing a new car radio so if you’re comfortable with this job, you’ll probably get by with it.
What should I do if the indicator and dashboard do not work?
If your gauges aren’t working and your dashboards and lights aren’t lit either, this is a sign that there may be a ground problem. This assumes that you have already checked the sensors fuse and determined that it is in good working order.
If the instrument cluster is not grounded properly you will usually find that the indicators and instrument lamp do not work or only work intermittently. You may be able to test the ground by looking under the dash under the flashlight, but in many cases you will have to actually remove the instrument cluster.
What if the sensors seem strange or the needles are attached?
When the sensors seem to move erratically or have the maximum delay possible, the problem is usually a bad component such as the instrument’s voltage regulator or a bad ground.
Erratic pickups, or pickups that seem to read uniformly low, are usually caused by a bad instrument voltage regulator. In some cases, you can remove the regulator, clean the connector terminals, and reinstall it.
Gauges that read full all the time are usually caused by a weak or bad ground. If you can locate the ground, either visually or with an electrical diagram, you need to make sure it is secure and no rust or corrosion .
Problem with electronic devices
In some cases, you may find that the entire instrument panel is defective. For example, if you have an electronic instrument cluster that doesn’t have separate sensors that receive independent inputs from separate senders, complete failure of all sensors often requires replacing the entire cluster.
Early electronic instrument clusters had digital readouts very similar to LCD alarm clock, while the modern equivalent often mimics analog sensors in a much more sophisticated way. Either way, diagnosing and repairing or rebuilding this type of instrument cluster is beyond the typical DIY option, unless you want to just replace it all and hope for the best.
What if only one sensor is not working?
When one sensor stops working, the problem is with the sensor, wiring, or sending device. If you are comfortable with finding and removing sending devices and sensors, you can diagnose this type of problem yourself. Otherwise, you will have to take it to a mechanic.
Using the coolant temperature sensor as an example, the diagnostic procedure involves finding and disabling the sender unit. With the ignition on, the sensor should register as cold. If you connect the sender’s wire to ground, the sensor should switch to the «hot» reading.
If the sensor is moving as expected, you may suspect a bad sending unit. If the sensor does not move when you ground the sensor wire, you may suspect a bad sensor. Similar tests can be performed on all sensors in your instrument cluster, although specific procedures may differ from one application to another.
When the speedometer doesn’t work
While all gauges can be either analog or digital, speedometers are unique in that they can be mechanical or electrical inputs . All other dashboards are wired to sensors or sending devices, while your speedometer can use either a speed sensor or a physical cable.
In vehicles that use cables, the speedometer is physically connected to the transmission through the cable. The cable is usually square at both ends, or square at one end and slotted at the other. When the cable breaks, the sensor may not move at all, or it may twitch a little.
The solution to this problem is to simply replace the speedometer cable, which involves unhooking it from the transmission, unhooking it from the instrument cluster, and then sliding it through the firewall. In many cases, this also requires the removal of the instrument cluster itself.
Faulty speedometers and speed sensors
Most modern cars and trucks use speed sensors instead of cables, and the transition began in the 1990s. Some cars even have a speed sensor and a cable, in which case the cable usually drives the speedometer and the speed sensor or wheel sensor tells the computer how fast the car is going.
The only way to know for sure what you have is to look at who you are, make and year, or physically inspect the back of the instrument cluster. If there is no cable connected to the back of the cluster, then your car has a speed sensor.
In vehicles with speed sensors, the easiest way to tell if a sensor or sensor is bad requires a system cruise control . Because cruise control also uses a speed sensor, it will not work correctly or not at all if the sensor is faulty.
If you find that your cruise control is working but the speedometer is not working, you should suspect a bad speedometer. The reverse is also true, so if your speedometer and cruise control are malfunctioning, you might suspect a faulty speed sensor or faulty wiring.