The needle on my temp gauge stays below the first line all the time. The check engine light is on and the code is for "coolant temperature below thermostat threshhold". I replaced the thermostat, but didn't have an impact. The heater warms up and blows hot air without any problem, even in 10 degree weather. I'm thinking the ECT Sensor may be faulty. Does that sound like the case to you? If so, where can I locate the ECT Sensor on my engine? It's a DOHC 3.0 liter engine. Thank you much!
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Depending on the year there isn't any . All done by computer on serial data bus communication network. The coolant temp. is supplied to the engine computer By a ETC - engine coolant temp sensor . All the modules on the vehicle ( ABS , air bags , BCM , instrument cluster , RKE module etc... ) Share info on this data bus network . If the gauge isn't working probably bad ,If a communication network problem the gauge will default to fixed temp degree . This is for a 1999 Buick , out of factory service repair manual . But all vehicles are pretty much the same .
Engine Coolant Temperature Gauge
The Powertrain Control Module (PCM) via the class II serial data line to the instrument cluster, broadcasts the coolant temperature. The instrument cluster compares the temperature data using a 16 point look-up table in order to determine the needle deflection. A smooth filter is used in order to secure a continuous response. The instrument cluster drives the temperature gauge to C (cold) under the following conditions:
• The temperature data is lost.
• The PCM is in a state of health fault.
Have you checked your cooling fan to see if it is working propely? Let the car idle and get warm and listen for the fan to kick in (if they are electric) or just watch to see if the fan starts to spin faster if it is the old school type with a clutch. Have you replaced the thermostat? A bad one will let the temp rise since it opens too late and then the temp will drop off. But it won't due this only at a light and it will do it infrequently.
Well sounds like first start your car record where the temp needle reads, then let the engine warm up (with out driving) then rev the engine to about 3500-4000rpm a couple times does your needle move at all record then hold your rpm at 3500 for about 5-10 sec does this get the gauge to drop? sounds like you may "if not over heating at all and coolant level and circulation is good" have a circuit problem, you can test this by going to auto zone and ask for a scan to be done on your car when the plug into your OBD 2 ask them to go into DATA STREAM and then check to see what temp your ECM thinks the engine coolant is at does it match your gauge at idle and at 3500rpm if not its a faulty circuit
It could be a plugged heater core or heater control problem. I assume the blower is working, but the air is cold. The first thing to check is the coolant level, make sure there is coolant in the resivoir. Next see if the temerature gauge reaches the normal operating temperature range. If the gauge reads cold most of the time, it would tell you that the thermsotat is faulty and not allowing the engine to reach full operating temperature. If your car doesn't have a temp gauge, the blue cold engine light might stay on for an extended period of time. The thermostat is supposed to not allow coolant flow in the radiator until the engine reaches operating temperature. If you drive the car for a couple of minutes, from cold start, the radiator or upper hose should be cool until the engine reaches operating temp.
Yadayada ,don't know where you came up with that . This vehicle has just one ECT - engine coolat temp. sensor . It's an input for the PCM - engine computer . The PCM sends this info to the instrument cluster over the class2 serial data bus. . The proper way to diagnose a problem like this would be to hook up a professional scanner an check input data to the PCM , an instrument cluster . Not guessing an replacing parts .
Engine Coolant Temperature Gage
The IPC displays the engine coolant temperature as determined by the PCM. The IPC receives a class 2 message from the PCM indicating the engine coolant temperature. The engine coolant temperature gage defaults to 60°C (140°F) or below if:
• The PCM detects a malfunction in the engine coolant temperature sensor circuit.
• The IPC detects a loss of class 2 communications with the PCM.
What engine ? could have come with a 3.4 or 3.8 L .
Engine Coolant Temperature (ECT) Sensor (L36)
Left side of the engine, below the thermostat outlet
Engine Coolant Temperature (ECT) Sensor (LA1)
LH side, top of the engine
Both are close to the thermostat housing , do you know what an where that is ? Follow the top radiator hose to the engine , should be near there . Look at the new part ,can't you match it up.
The sensor you replaced was the ECT (engine coolant temp)? Check your coolant level and air in the lines. Do a coolant pressure test to make sure the cooling system holds pressure, If it doesn't, you may have a head gasket problem.