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How to Fix Malfunctioning Dashboard Gauges
Time: 2018-01-23
The dashboard gauges in your car tell a complex story about everything from your current rate of speed, to the state and health of your engine, and even whether or not things like your headlights are switched on.
When one gauge stops working, the problem may be in the gauge itself or a bad sensor, while all the gauges cutting out at the same time often indicates a blown fuse or a defective instrument cluster.
There are a lot of different types of instrument cluster designs and configurations, but when all of the gauges in a car stop working at once, the problem is usually either a fuse or wiring problem. The first step in diagnosing this type of issue is to identify fuse associated with the instrument cluster or gauges. The fuse should have power on both sides when the ignition key is turned to the on position. You can check this with an inexpensive test light or multimeter, or take your car to a mechanic if you don’t have the right tools or aren’t comfortable digging into a diagnostic like this.
If the fuse is good, the next thing you or your mechanic will want to do is to check for power at the individual gauges. This usually requires removing the instrument cluster, which can be quite difficult and time-consuming in some vehicles.
If your gauges don’t work, and your dash lights and indicators also fail to illuminate, that’s a clue that there may be a ground issue. This assumes that you have already checked the gauges fuse and determined that it’s in good working order.
When an instrument cluster isn’t properly grounded, you’ll typically find that the gauges and dash lights fail to work or only work intermittently. You may be able to check the ground by looking up under the dash with a flashlight, but you will have to actually remove the instrument cluster in many cases.
When the gauges seem to move erratically, or they are pegged at the highest possible reading, the problem is usually a bad component like an instrument voltage regulator or a bad ground. Erratic gauges, or gauges that seem to read uniformly low, are usually caused by a bad instrument voltage regulator. In some cases, you may be able to remove the regulator, clean the connector terminals, and reinstall it.
In some cases, you may find that the entire instrument cluster is bad. For instance, if you have an electronic instrument cluster that doesn’t have separate gauges that receive independent inputs from individual sending units, a total failure of all the gauges often requires the replacement of the entire cluster.
Early electronic instrument clusters had digital readouts much like an LCD alarm clock, while the modern equivalent often simulates analog gauges in a much more sophisticated way. In either case, diagnosing and repairing or reconditioning this type of instrument cluster is outside the realm of the typical do-it-yourselfer, unless you want to just replace the entire thing and hope for the best.
*When a Single Gauge Stops Working
When a single gauge stops working, the problem is either in the gauge, the wiring, or the sending unit. If you are comfortable locating and removing sending units and sensors, you can diagnose this type of problem yourself. Otherwise, you’ll have to take it to a mechanic.
Using your coolant temperature gauge as an example, the diagnostic procedure involves locating and disconnecting the sending unit. With the ignition on, the gauge should register cold. If you connect the sending unit wire to ground, the gauge should switch to read hot. If the gauge moves as expected, then you can suspect a bad sending unit. If the gauge doesn’t move when you ground out the sensor wire, then you can suspect a bad gauge. Similar tests can be performed on all of the gauges in your instrument cluster, although the specific procedures can differ from one application to another.
*Malfunctioning Speedometer
While all gauges can be either analog or digital, speedometers are unique in that they can have either mechanical or electrical inputs. All other dash gauges are connected to sensors or sending units via wires, while your speedometer may utilize either a speed sensor or a physical cable.
In vehicles that use cables, the speedometer is physically coupled to the transmission via a cable. The cable is usually square on both ends or square on one end and slotted on the other. When the cable breaks, the gauge may not move at all, or it may jerk a little intermittently. The fix for that problem is to simply replace the speedometer cable, which involved unbolting it from the transmission, disconnecting it from the instrument cluster, and then sliding it through the firewall. In many cases, this also requires removing the instrument cluster itself.
Most modern cars and trucks use speed sensors instead of cables, and the transition started in the 1990s. Some vehicles even have both a speed sensor and a cable, in which case the cable usually drives the speedometer while the speed sensor or wheel sensor tells the computer how fast the vehicle is moving.
The only way to know for sure what your car has is to either look up your make, model and year or to physically inspect the back of the instrument cluster. If there is no cable attached to the back of the cluster, then your vehicle has a speed sensor.
In vehicles that have speed sensors, the easiest way to determine whether the sensor or gauge is bad requires the presence of a cruise control system. Since cruise control also makes use of the speed sensor, it won’t operate correctly, or at all, if the sensor is bad. If you find that your cruise control works, but your speedometer isn’t working, then you should suspect a bad speedometer. The reverse is also true, so if both your speedometer and cruise control are malfunctioning, you can suspect a bad speed sensor or faulty wiring.
In less common circumstances, the electronic control unit (ECU) could also be malfunctioning. If you take your car to a qualified technician, they will be able to connect to the ECU to read trouble codes and other data. Using specialized testing equipment, they will also be able to actually test the speed sensor itself.
Source: www.lifewire.com