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XC90 "Coolant Low - Stop the Car!" Warning - May be a simple repair w/o replacing the coolant level sensor!

Help, Advice, Owners' Discussion and DIY Tutorials on Volvo XC90s. The XC90 proved to be very popular, and very good for Volvo's sales numbers, since its introduction in model year 2003 (North America).
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XC90 "Coolant Low - Stop the Car!" Warning - May be a simple repair w/o replacing the coolant level sensor!

Post by ALF1 »

This repair applies to all XC90 and similar Volvo's that have Coolant Level Sensors fitted into the bottom of the Coolant Overflow Tank.

- As usual, you take guidance from this story at your own risk and I make no claims to its applicability.

- Many repairs are available to the DIYer are on the front passenger side of the engine including timing belt replacement, serpentine belt replacement, alternator, A/C compressor, Power Steering Pump and others. Most of these begin with relocating the opaque clear plastic Coolant Overflow Tank and the black plastic Power Steering Fluid tank from their installed locations to above the engine to get them out of the way and provide additional room for hands and tools during the repair. Fortunately, the relocation of the Coolant Overflow Tank does not require you to empty it, albeit you may need to disconnect the level sensor wire connector from its partner leading to the car.

While performing the full set DIY repairs including replacing the timing belt, water pump, timing belt tensioner, timing belt pulley, serpentine belt, serpentine belt tensioner and the alternator on my 2003 Volvo XC90 2.5T with 210,000 miles, I relocated my Coolant Overflow Tank and then returned it to its proper position without issue.

I then experienced the scary "Coolant Low - Stop the Car" warning with Red Triangle symbol even though the coolant level was full and the engine temperature was normal.

Strange, I went and had the codes read and there was nothing to indicate what other type of problem could cause this. Squeezing the upper coolant hoses also confirmed that coolant was everywhere. I sweated a few days, checked the forums and youtube videos and looked at replacement sensors. One of the forums suggested that perhaps the float detected water rather than 50:50 mix.

I then decided to inspect if the float was stuck...nope that was not it. I then decided to inspect the sensor (hey, you don't need to remove any coolant to do this.)

I flipped the Coolant Overflow Tank over and noticed two black wires entering the end of a 1/4" diameter rod like black plastic fitting which fits into a bottom port on the Coolant Overflow Tank. This is the Coolant Level Sensor. The Coolant Level Sensor is a magnetic pickup and is designed to pickup of the position of the float inside the Coolant Overflow Tank. Upon inspection, I noted that the two wires that entered the sensor had been pulled out a few millimeters during my handling of the Coolant Overflow Tank.

I pushed the wires back in and the "Coolant Low - Stop the Car" warning disappeared. This makes sense if the pickup is on the end of the wires.

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Re: XC90 "Coolant Low - Stop the Car!" Warning - May be a simple repair w/o replacing the coolant level sensor!

Post by oragex »

Just to ad that this sensor goes bad when the coolant reservoir is lifted without disconnecting the sensor's electrical plug.
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Re: XC90 "Coolant Low - Stop the Car!" Warning - May be a simple repair w/o replacing the coolant level sensor!

Post by SnowOwl »


I am getting the Low Coolant -Stop Engine message on my S60 and the coolant level is normal. I took the reservoir off and looked at the wires in the bottom, but jiggling/pushing them didn't seem to make them go in at all. I couldn't get my other hand on the connector so I couldn't take it apart, but I kind of jiggled everything I could to try to make a better connection.

Let me describe what I saw. Two wires come out of the bottom of the reservoir, about 18 gauge and there was a sleeve, about /'4" diameter those wires went into, and then came back out of and went into the connector. Could the sleeve be the rod you thought should be stuck up into the reservoir? I guess I'll poke at that tomorrow.

How did you determine that the float wasn't sticking? I couldn't identify it.

Thanks again...
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Re: XC90 "Coolant Low - Stop the Car!" Warning - May be a simple repair w/o replacing the coolant level sensor!

Post by ggleavitt »

Pretty old but not much has changed over the years- viewtopic.php?t=46131#p226142 can get you started. If it's a 2.5T, anyone who's yanked up on the reservoir more than once can recall how easy it is to do it and more than one sensor has not been disconnected before removal (like noted above). Had to replace mine once for this very scenario.
Good luck!
2006 V8 AWD VOR-135k
2008 V8 AWD Sport-135k
2005 2.5T AWD-202k
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