2002 Volvo S60 - Overheating Message on Dash
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General Information: The customer came in with the complaint of the overheating message on the dash even when the car is just started. The customer thinks that the car is not overheating, but decided not to drive the car just in case.
First Thoughts: I thought this would be an interesting case study, because of the odd behavior of the dash message. I confirmed the complaint of the customer, and the message does come on a minute after it has been running. Sometimes it would come on immediately, most of the time it would come on after running about a minute. I first thought maybe it could be a coolant sensor messing up or maybe a bad dash cluster. It could also be a wiring issue, like a bad connection or loose connection.
Diagnostics: I decided to connect the Snap-on Zeus scanner to the car. I just wanted to see what data the engine computer was receiving from the engine coolant temperature sensor.
The weird thing was when I plugged my scan tool in, it worked fine and there were no messages on the dash, but then at around 155 degrees, it glitched. I just so happen to catch it with the screenshot above.
I decided to connect the lab-scope to the wiring at the sensor to see if it’s a sensor problem or connection.
The lab-scope showed that the engine coolant temperature sensor was glitching with the signal it was sending back to the engine computer.
On this vehicle, the computer sends a 5 volt reference to the sensor and depending on the temperature of the engine, it will change the voltage. The engine computer then interprets that voltage to send to the dash for the temperature gauge and also uses the data for other engine systems.
The pictures above show that the engine coolant temperature sensor is receiving the 5 volt reference and is changing it to around 1.4 volts, which means it’s working. But the areas where it jumps to 5 volts means that the sensor is glitching and not giving constant accurate data. I noticed that the small glitches do not cause the message to appear on the dash, but the long glitches do cause it to appear.
I tried wiggling wires and the connector on the sensor, but it did not change anything. So the conclusion is that this vehicle needs an engine coolant temperature sensor.
After the repair was done, the message on the dash did not come back on!
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