One of the most inconvenient things that can happen to your 9-5 is when the speedometer stops working. You don’t really realize how much you look at the thing until it’s just always sitting at 0 MPH while driving down the road.
If your Saab 9-5’s speedometer is not working, it’s usually going to be caused by an issue with the VSS (vehicle speed sensor), or a bad ECU. The VSS is usually not very expensive, and they are not that difficult to replace.
Vehicles used to use a cable that would usually run from the tail shaft of the transmission to the speedometer. There was a physical/mechanical connection between the drivetrain and the speedometer.
Instead of this direct connection, a modern vehicle uses the vehicle speed sensor and relays that information to the speedometer. The VSS is one part of a system of sensors that helps keep you safe (traction control, ABS, cruise control).
Speedometer Not Working Causes: Saab 9-5
A modern vehicle’s speedometer takes the input from the Vehicle Speed Sensor and sends that data to the ECU. The ECU is programmed with your 9-5’s gear ratios and stock tire height. It combines this data to send the speed reading to the instrument cluster. The causes of a bad speedometer will typically be found in these four things:
- VSS– A faulty speed sensor will often be accompanied by the P0500 (VSS circuit malfunction) trouble code. The speed sensor does more than just control the speedometer, it also helps to control the cruise control system and may even affect the way that the engine runs. If the service engine soon light is on, then check the trouble code with an OBDII scanner. If you don’t have a scanner, take it to the local parts store and have them run it for you.
- Wiring Issues– Exposed wiring to or from the VSS can cause your 9-5’s speedometer to no longer work. This will often manifest itself after driving through heavy water. It’s worth checking to see if the fuse has blown. If it has, just be aware that it will eventually blow again without addressing the cause of the problem. Here’s a great guide on how to diagnose a wiring short in almost any vehicle
- ECU– Your 9-5’s Engine Control Unit (ECU for short) is the computer that takes all of the information that the vehicle sensors compile and uses it to control the vehicle systems, and sends important vehicular telemetry data to the driver via the instrument cluster. If there is something wrong with the ECU, it may no longer be able to send the speed telemetry to the instrument panel. This one is a possibility if there are no VSS related trouble codes, but taking a look at the wiring would be a better place to go before taking a look at the ECU.
- Speedometer Itself– The odds of the speedometer going out all by itself, while the rest of the gauges continue to work are not great. Most of the time if the speedometer is out, it means that there is a bigger problem with the entire instrument cluster. Do all of the other gauges work? If yes then, the problem is probably not in the speedometer, but the signal going to it. Other gauges went out too? Ok, looking at the instrument panel and ECU are going to be where to start. Instrument panel first.
9-5 Speedometer Not Working Diagnosis
If your Saab 9-5’s speedometer is not working, the first place to go would be to check the service engine soon light (if applicable). Now, take it out and see if the cruise control still works. If it does, that’s a pretty good indication that the vehicle speed sensor is just fine. If it doesn’t, it’s time to take a look at it.
After testing the cruise control, you would want to move on to the VSS and the wiring going to and from it. Before sticking your head under the vehicle, check to see if the fuse going to the VSS is blow. If it is, replacing it may temporarily restore your 9-5’s speedometer, but that doesn’t fix why the speedometer stopped working. If everything still checks out, it’s time to move on to the ECU.
Driving without a speedometer can be somewhat dangerous and off putting. We recommend using a speedometer app. They use the GPS built into your smartphone to give a very accurate speed reading. You can throw it on your dash until you get it fixed. Good luck fixing your 9-5’s speedometer! If there is anything that you would like to add, please feel free to leave a comment below.