This article will explain some basic testing procedures and common fixes for problems with the coolant gauge. When diagnosing any coolant temperature problem the first thing you need to do is make sure the cooling system is operating properly and the vehicle is running at a normal operating temperature. If you’re having problems with your coolant gauge not reading correctly and it’s related to something in the cooling system you will probably find the problem during your cooling system operation inspection.
Check the fans are cycling properly and for proper operation of the thermostat. Next you need to read the coolant temperature sensor and if you have a scanner it makes it easy but if not, no worries you can just jump straight to the test you would have to do if you were having coolant temperature sensor problems anyways. Most every automotive manufacturer uses a 5v reference for their coolant temperature sensors. Then there will be a ground, check it and makes sure it’s good then backprobe the 5v reference and plug in the sensor. Monitor the voltage as the vehicle warms up (while running of course) and the voltage should slowly rise as the resistance drops in the thermistor.
- a semiconductor device having a resistance that decreases rapidly with an increase in temperature. It is used for temperature measurement, to compensate for temperature variations in a circuit, etc.
Now as for Subaru’s and cooling gauge problems there are basically only two things that I have go wrong with them in the years of working on these cars. There are other things that could go wrong but I just don’t ever see it. For example VW and Volvo are common to have instrument cluster circuit problems and instrument cluster control module issues, where the controller is located in the instrument cluster. So usually it’s going to be the gauge itself or the sensor. I will show you how to test and/or replace both. The sensor is pretty, look at the gallery pictures below to get an idea of its location. Now most vehicles use a two-wire temperature sensor and a one-wire sender that would be for the gauge. The other two-coolant sensor is for the computer. Subaru uses one dual function sensor so you will see a three-wire sensor. They share a common ground and the other two wires are volt references to the gauge and PCM. Find the three-wire sensor in the water crossover pipe under the intake manifold, just right of center. Black/Yellow wire is for the PCM, Black is the ground and the White/Green wire is the thermistor for the gauge. First check for a 10V reference from the gauge on the White/Green wire. Next ground the White/Green wire through a test bulb, something that draws current, not an LED test light. When you ground this wire the gauge should raise if it doesn’t then the gauge is faulty, if it raises then your problem is in the sensor. Now replacing the gauge is pretty easy, just be sure to inspect the instrument cluster circuit board at the main connector solder points, I have seen breaks there before in other vehicles never a Subaru though. You should be able to get a gauge from the Subaru dealer for less that $30.00 and the sensor is a little more expensive but either way this can be a relatively inexpensive fix that can prevent costly engine damage from not having a properly working coolant gauge. Well, that’s about it. Take a look at the gallery images below for pictures on hoe to remove the instrument cluster. These pictures refer to a 2003 Subaru Legacy. The older models didn’t require so much work to get the cluster out but these you have to remove a lot of trim parts and lower the steering column (2 bolts). Subscribe to my blog, LIKE my page, thanks for reading.