U0116: Lost Communication With Coolant Temperature Control Module
What to do
Keep an eye on the temperature gauge and treat any rise as genuine.
Modern engines control their own temperature actively — electric pumps and motorised valves rather than a simple thermostat — and this code means the computer doing that has stopped talking to the rest of the car. Whatever position things were in when it went quiet is where they have stayed.
Most often that means an engine that never properly warms up: a heater that takes far too long, higher fuel consumption, possibly the engine light. Not urgent, but not harmless either.
The version to take seriously is the opposite one. If the coolant has stopped circulating, nothing warns you until the temperature climbs. Steam or a sweet smell from the engine bay, or a heater that suddenly blows cold, means stop and switch the engine off rather than carry on to the next town.
Ask for the fuses to be checked first. This module's supply often shares a fuse or relay with the cooling fans, so one blown fuse can take out several things at once — and that is the cheapest possible answer.
What this code means
The coolant temperature control module has stopped being heard from. The general reasoning is at U0100, and U0456 explains what this module does and why a modern engine has one.
The difference between silence and bad data matters here more than it might sound. A module reporting an implausible temperature makes the engine module assume the worst and run full cooling. A module that has gone silent leaves the valves and pump wherever they were when it stopped, which is not necessarily anywhere useful.
So the two failure pictures are opposite and the driver can tell them apart for free.
- Stuck cold — the valve parked open and the pump running — gives an engine that never warms up, a heater blowing cool, and the fuel consumption and cold-running wear that go with it. Annoying rather than urgent.
- Stuck hot or stuck shut is the one to take seriously. An electric coolant pump that has stopped moving water does not announce itself the way a broken belt does, and on a turbocharged engine the pump also runs after shutdown to carry heat out of the turbo. Losing that quietly cooks bearings over months.
So watch the temperature gauge and treat any rise as real. Steam, a sweet smell, or a heater going suddenly cold means stop and switch off rather than press on.
Where the fault usually is: this module lives in the engine bay, in the heat. Its connectors are heat-cycled thousands of times, and its supply commonly shares a fuse or a relay with the cooling fans — so a blown fuse takes out more than one thing at once, which is the cheap answer and the first one to check.
Likely causes
Start here
- Blown fuse or failed supply · easy
- Failed power or earth supply to the module · moderate
- Corroded or loose connector · easy
- Heat damage to sensor or wiring · moderate
Less common
- Damaged data bus wiring · moderate
- Another module holding the bus down · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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