S40 temp / over heating

Possible water pump failure. Was temp guage showing "hot" ? , if not maybe coolant sensor issue. Had the car just been driven hard ? Any pressure in coolant expansion tank ?

Check your temp sensor(s).

You need to look at the temp sending unit it's probably faulty anthor issue with volvo is dirty throttle body's this raises havoc on the car they idle up down all over the map also you should change the thermostat too as a precautionary measure make sure it's the right temp for your year of your car thanx Chris

Engine temp sensor or fan relay is going bad.

I’m happy to assist further over the phone at https://www.6ya.com/expert/gregg_78ecbb34e27be215

it could be one of 2 things the cam sensor or the co sensor on the exhaust, both of these when warmed up will set off an eml light and confusing error codes. as when engine is stopped they reset themselves. but codes will be logged and they need to be warmed up again. cam sensor faults is when the resistance in the sensor become erratic. as it has volts on the sensor will go up and down. co sensor can be the heater as it has to heat the sensor to make the sensor reliable. it takes a few seconds for the sensor to read. if it fails and come up on eml light but then turn engine off and then start it again it can be this cam and crank sensors work the same way they can over heat them selfs of time and will both need replacing, i found its best to replace both at the same time.

1st lets look at the explanatioon of this code, it is not always the sensor at fault, the sensor can just be a symptom of another problem.

Causes A code P0133 may mean that one or more of the following has happened:

• The oxygen sensor is faulty
• The wiring to the sensor is broken / frayed
• There is an exhaust leak

Possible Solutions The simplest thing to do is to reset the code and see if it comes back.
If the code comes back, the problem is more than likely the front Bank 1 oxygen sensor. You will likely wind up replacing it but you should also consider these possible solutions:

• Check and fix any exhaust leaks
• Check for wiring problems (shorted, frayed wires)
• Check the frequency and amplitude of the oxygen sensor (advanced)
• Check for a deteriorating / contaminated oxygen sensor, replace if necessary
• Check for inlet air leaks
• Check the MAF sensor for proper operation

if it is not missing then the problem is most likely engine mounts that have gotten hard from heat, this is the common reason and the 1st thing we look at if the engine is running ok and not the source of the chassis vibration.

Replace the thermostat. If thermo is stuck open, coolant only heats up when there is no flow over radiator(idle) and then cools down when driving. Also, check coolant level, same response as stuck thermo.