Check engine light(coolant temp. always too low) and car is sometimes very hard to start?

Coolant temp sensor tells the engine computer the engine temperature so that it can make changes in injector pulse width and timing. If coolant sensor is bad it can cause all sorts of problems. Relying on Autozone's $7.50 per hour help to diagnose car problems is not usually a good thing to do , but in this case I think maybe they are correct. Replace the sensor.

A good mechanic should measure the actual coolant temp and compare it to the sensor reader on a professional grade scan tool. If the temp is higher than the scan tool indicates, that would warrant replacing the sensor. If the actual temp is low and matched the sensor reading, then the problem lies elsewhere.

The cold start problem indicates that it may not the coolant temp sensor. When the engine is cold, the ecu runs the engine in "open loop" mode, and forces the ignition timing and air-fuel mixture based on an internal table of preset values. When the engine warms up, however,the ecu calculates the mixture and ignition from reading taken from several sensors

Possible problems other than the coolant temp sensor are:

Vacuum leak or air leak between the air filter housing and throttle body,

bad thermostat

sensor creep in the IAT, O2, and MAP/BAP sensors (if so equipped

corroded or damaged sensor wiring.

bad plugs or plug wires

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Check engine light(coolant temp. always too low) and car is sometimes very hard to start?

Ok. I have a 97 Dodge Avenger ES with the 2.5L V6. My check engine light went on on thursday morning, and I took it to autozone that night to get it checked out. They said that the coolant temperature was always to low and recommended I purchase a new coolant temp. sensor. Since I didn't...

Low Coolant Temperature

The light will come on and go off periodically. That is normal. The coolant sensor tell the computer what temp the coolant is. That in turns tell the computer how much to let the injectors to spray. When the engine is cold it needs a little more fuel to run correctly. As the motor warms up the fuel is decreased until the motor is running at peak temperature. replace the sensor and your starting problem will go away.

When starting a gas engine from cold you must enrich the fuel air mix. Traditionally a choke was used for this but with the introduction of fuel injection replacing the carburettor, another system has developed to enrich the mix. The engine management system must know the engine temperature at all times to ensure the fuel air mix is correct, if the temperature sensor is malfunctioning, this can not happen. So on cold days the engine management system is unaware of the cold and does not enrich the fuel air mix, and the engine won't start. It starts fine when it's hot because this is the assumed default temperature,

Change the temperature sensor or at least check the plug on it.

I have a '96 plymouth neon that has almost exactly the same problems as yours seems to have. The check engine light on my car used to come on, and stay on, when seemingly nothing was wrong. My car also started to take a lot longer to start when it got really cold outside, and the idling sounded terrible. We thought that it might be the gas, so I usually try to keep the tank almost full and add dry gas to it. Sometimes that works. As for the engine light... I don't really know what to tell you. My speedometer doesn't work sometimes either. (Manufacturing defect.) <3 plymouth I hope I was a little helpful, at least.

START issues are NEVER usually due to the TEMP SENSOR< but can be on a few types of cars! START ISSUES are almost ALWAYS due to a dirty THROTTLE BODY and IDLE AIR CONTROL VALVE and clogged up PCV valve from using CHEAP OIL CHANGES! If the TEMP SENSOR gives a BAD signal it can affect starting a bit on SOME cars! Get a good BORG WARNER replacement part for your CHRYSLER. Change the COOLING FAN SWITCH as well but START with a cleaned up IAC and T body FIRST! Use BOSCH Or DENSO iridium plugs for MORE POWER and economy as our NEWEST LOW SULFUR FUELS react with it at the MOLECULAR LEVEL to get MORE COMPLETE and LOWER emissions BURN! Use ONLY MOBIL ONE 0W-30 and NO MORE VALVOLINE that NO factory on earth uses ANYWHERE! It makes SLUDGE and leaves TAR and WAX behind and CLOGS UP ENGINE SENSORS as you will NOW see! GOOD LUCK!!

Replace your sensor. the part of your story about hard start when cold but easy start when warm confirms it. The sensor probably went bad in the hot position and now tells your computer that the engine is hot already when you go to start it during a cold morning. Now the computer thinks it is hot and it leans the fuel mixture going to the injectors, so less fuel makes for harder starts in cooler weather. Got it?? Hope so and just replace the sensor.

good luck......

bad coolant temp sensor or engine temp sensor. Names are different depending on manufacturer.