What is the common cause of car wont start in diesel engine?

it could mean your engine is having trouble producing a spark, getting fuel, or creating compression. The most common causes are in the ignition (for example, a bad ignition coil) or fuel system (for example, a clogged fuel filter). Hope this help

Possibly though there are many variables. If the sensor is doubtful why not check the output if you have the facility or just replace it if it is a reasonable price.

This is known as 'dieseling'. The most common causes are

-idle speed set too high

-engine operating too hot (faulty thermostat, faulty temp sender, leaky head gasket)

engine timing is out (loose distributor clamp, worn timing belt, faulty timing belt tensioner)

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We do not have Toyota diesels here. But common reasons for this are a failed engine timing gear or a failed low pressure fuel pump also known as a "pickup pump"

Have you run a scanner on this?

You don't say whether it is petrol or diesel engined or whether the engine is cranking fine but won't fire.

Certainly an engine must crank quick enough but even then if it is the best diesel engine ever made it is unlikely to start below freezing without an artificial starting aid. Such an aid is already installed but must be in good condition. Heater plugs do fail sometimes or get tired and lazy so they need checking and sometimes the timer relay fails to switch them on. Good injector spray patterns are also needed for good starting.

Petrol engines need enrichment of the fuel/air mixture for cold starting and a very good spark at the plugs. Worn spark plugs is the most common cause of poor starting and if the ECU isn't getting the right information about temperature it will be unable to make the correct fuel adjustments.
A good injector spray pattern is also important.

Lots to think about...

If no fuel to engine I'd be looking at fuel pump rather than temp sensor,also known for blocked fuel filter to cause same problem

I'm not much on diesels, but for gas engines the most common source is a leaking injector or fuel pressure regulator.

try disconnecting the battery and joining the leads together leave for half hour and try again ,Seems to be common fault on these cars with teh computer and i have no idea whats causing it to do this but i do know that joining the leads together clears the fault sometimes

Never, ever use starting fluid in your diesel.

Taken from the Owners Manual - Diesel Supplement:

Do not crank the engine for more than 30 seconds at a time as starter
damage may occur. If the engine fails to start, turn the key to OFF and
wait 30 seconds before trying again.
Do not use starting fluid such as ether in the air intake system (see Air
Cleaner Decal). Such fluid could cause immediate explosive damage to
the engine and possible personal injury.
Do not add gasoline, gasohol or alcohol to diesel fuel. This practice
creates a serious fire hazard and causes engine performance problems.
1. Make sure all vehicle occupants have buckled their safety belts. For
more information on safety belts and their proper usage, refer to Seating
and safety restraints chapter in the owner guide.