Where are the coolant sensors on a1985 corvette. the one that goes to the instrument cluster and the one that goes to the ecm.

More than likely a broken wire, corroded connector or a chafed wire.

Are any DTC'S - diagnostic trouble code's stored in any module ? BCM - body control module , PCM - engine computer ,IPC etc.... It's the temp. gauge not thermostate gauge Did it work after replacing the thermostate an coolant temp sensor ?
Engine Coolant Temperature Gage
The instrument panel cluster (IPC) displays the engine coolant temperature as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the engine coolant temperature. The engine coolant temperature gage defaults to 38°C (100°F) if:
• The ECM detects a malfunction in the engine coolant temperature sensor circuit.
• The IPC detects a loss of serial data communications from the BCM.

The first thing too do would be to hook up a factory or some other type of professional scan tool an see what the temp. sensor is telling the engine computer an if the BCM is showing the same temp. data . And is that info. getting to the instrument cluster . Knowledge of how it all works an proper diagnostic technique is the key to finding the problem .
If the IPC is see same temp the engine computer is an the gauge isn't working something is wrong with the gauge itself. New instrument cluster would be needed .

Without testing ,hard to say for sure . Gauge could be going bad or the engine coolant temp sensor , wiring for sensor , PCM/ECM etc..... Knowing where that info originates an how it gets to the instrument cluster gauge is key in diagnosing the problem . Having worked at GM dealer ships an having correct tools an information gives me an edge over most . Most people would just replace parts an hope it fixes it . The first place to start would be to hook up a factory or professional scan tool an check for DTC'S - diagnostic trouble codes in the instrument cluster an the PCM/ECM . View live data inputs from the coolant temp sensor to the PCM?ECM - engine computer ,also see if that same info is getting to the instrument cluster . Most usually , if the problem is happening at the time we can't find the fault .
The Coolant temp sensor is an input to the PCM , the PCM sends this if to the instrument cluster on the serial data network . Don't know if you know what that is ?

Engine Coolant Temperature Gage
The instrument panel cluster (IPC) displays the engine coolant temperature as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the engine coolant temperature. The engine coolant temperature gage defaults to 100°F (40°C) or below if:
• The ECM detects a malfunction in the engine coolant temperature sensor circuit.
• The IPC detects a loss of serial data communications with the BCM.
• The BCM detects a loss of serial data communications with the ECM.

GM did have problems with stepper motors inside instrument clusters 2003 to 2006 . Stepper motors are what control the gauge needles .
https://www.youtube.com/watch?v=oTm2oDx-_GM

Why ? Temp gauge not working , showing the vehicle is over heating ? Is the check engine light on ? IF not probably not the temp sensor . GM had bad stepper motors in the instrument cluster , 2003 to 2006 The engine coolant temp sensor is a input to the PCM/ECM - engine computer . The temp info is sent to the instrument cluster over the class 2 serial data bus. You may want to have a qualified repair shop check it .

First off you would need to know from where an how this data get's to the instrument cluster , Computers involved ( control module's ) etc... serial data network - how the computers (modules ) communicate . Special tool's involved in testing this data - factory or professional scan tool - to view data from sensor's - temp sensor , fuel level sending unit in the fuel tank . Both of the these sensors are input's to the PCM/ECM - engine computer , which shares this info to other module's which need this info. The GMLAN serial data network is the data network which does this .
The instrument cluster has a microprocessor inside which view's this data an controls stepper motors to drive the gauge need .
Not working correctly or not at all can becaused by any number of thing's . The instrument cluster could have DTC'S - diagnostic trouble code's stored . Auto part stores can not read these code's or BCM code's . .
Engine Coolant Temperature Gage
The engine control module (ECM) calculates the engine coolant temperature as determined by the coolant temperature sensor. The ECM sends the engine coolant temperature to the body control module (BCM) via the serial data circuit. The instrument panel cluster (IPC) displays the engine coolant temperature when the BCM sends a serial data message to the IPC indicating the engine coolant temperature. The engine coolant temperature gage defaults to 0° or below if:
• The ECM detects a malfunction in the engine coolant temperature sensor circuit.
• The IPC detects a loss of serial data communications with the BCM.
• The BCM detects a loss of serial data communications with the ECM.
Fuel Gage
The engine control module (ECM) sends the fuel level percent to the BCM via the serial data circuit. The IPC displays the fuel level as received from the BCM. The fuel gage defaults to E (empty) if:
• The ECM detects a malfunction in the fuel level sensor circuit.
• The IPC detects a loss of serial data communications with the BCM.
• The BCM detects a loss of serial data communications with the ECM.
When the fuel level is less than a pre-determined value, the Low Fuel indicator message illuminates.

Your best bet , take your vehicle to a qualified repair shop.

Doesn't have a fuse just for the gauges . B+ power supply for the whole instrument cluster . Gauge info comes from the BCM - body control module an the PCM - powertrain control modules over serial data network (GMLAN ) The instrument cluster has electronics inside ,plus software . GM did have stepper motor problems in their instrument clusters from 2003 to 2006 . Your best bet , take it to a qualified repair shop.
How to repair GM Instrument Cluster Speedometer Gauge Stepper
Engine Coolant Temperature Gage
The engine control module (ECM) sends the coolant temperature to the instrument panel cluster (IPC) via serial data circuit. The IPC receives serial data messages from the BCM indicating the engine coolant temperature. The engine coolant temperature (ECT) gage, if equipped, defaults to 75°C (160°F) or below if:
• The ECM detects a malfunction in the ECT sensor circuit.
• The IPC detects a loss of serial data communications with the ECM.
Refer to Cooling System Description and Operation for more information.
Speedometer
The instrument panel cluster (IPC) displays the vehicle speed based on the information from the engine control module (ECM). The ECM sends a 4,000 pulse per mile signal to the cluster discretely. The IPC calculates the vehicle speed using the time difference between consecutive pulses. The speedometer will default to zero if the time duration since the last speed pulse is greater than or equal to one second.

Fuel Gage Description and Operation
The ECM uses the signal circuits of the primary and secondary fuel level senders to calculate the percentage of fuel remaining in the fuel tank. The ECM supplies 5 volts via the 5 volt reference circuit and also provides a low reference to the primary and secondary fuel level senders. When the fuel tank is full, the resistance of both fuel level senders are high and the ECM senses a high signal voltage on both the signal circuits of the primary fuel level sender and the secondary fuel level sender. When the fuel tank is empty, the resistance of both fuel level senders are low and the ECM senses a low signal voltage on both the signal circuits of the primary fuel level sender and the secondary fuel level sender. The engine control module (ECM) sends fuel level information to the instrument panel cluster (IPC) via serial data circuit. The instrument panel cluster (IPC) displays the fuel level information in the fuel gage. When the fuel level is less than a predetermined value, the low fuel message displays in the driver information center (DIC).
The fuel gage defaults to empty if:
• The ECM detects a malfunction in the fuel level sensor circuit.
• The IPC detects a loss of serial data communications with the ECM.

What diognostics say its a sensor ?????? No diagnostic's ever tell's you it's a sensor . You as a technician would need to prove that by testing electrical circuits , viewing coolant temp sensor . Hooking scan tool and trying to command the gauge with by directional control . The temp gauge not showing any temp. ? No movement ? Engine Coolant Temperature Gage Inaccurate or InoperativeStep Action
Yes
No
Schematic Reference: Instrument Cluster Schematics
1
Did you perform the Instrument Cluster Diagnostic System Check?
Go to Step 2
Go to Diagnostic System Check - Instrument Cluster
2
Install a scan tool.
Turn the ignition ON, with the engine OFF.
With the scan tool, perform the Lamp and Gauge Check in the IPC Special Functions list.
Does the engine coolant temperature gage move up and down when commanded?
Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
Go to Step 3
3
Replace the IPC. Refer to Instrument Cluster Replacement .
Did you complete the replacement?
Go to Step 4
--
4
Operate the system in order to verify the repair.
Did you correct the condition?
System OK
Go to Step 2
Would hate for you to replace the coolant temp sensor an find out that's not the problem ! Does the vehicle start an run good ,trans mission shift good ? If so it's not the coolant temp sensor .
Engine Coolant Temperature Gage
The ECM sends coolant temperature as determined by the coolant temperature sensor to the BCM via CAN serial data. The IPC displays the engine coolant temperature with the gage when the BCM sends a class 2 message to the IPC indicating coolant temperature percentage. The engine coolant temperature gage defaults to cold (0°) or below if:
• The ECM detects a malfunction in the engine coolant temperature sensor circuit.
• The IPC detects a loss of class 2 communications with the BCM.
• The BCM detects a loss of CAN communications with the ECM.

The engine control module (ECM) calculates the engine coolant temperature as determined by the coolant temperature sensor. The ECM sends the engine coolant temperature to the body control module (BCM) via the serial data circuit. The instrument panel cluster (IPC) displays the engine coolant temperature when the BCM sends a serial data message to the IPC indicating the engine coolant temperature. The engine coolant temperature gage defaults to 0° or below if:
• The ECM detects a malfunction in the engine coolant temperature sensor circuit.
• The IPC detects a loss of serial data communications with the BCM.
• The BCM detects a loss of serial data communications with the ECM

The place to start would be to hook up a factory or professional scan tool to see what the actual coolant temperature is ! At the PCM then at the BCM and finally at the instrument cluster . If normal the gauge is bad . The instrument cluster would need to be taken out of the vehicle an sent to be repaired . Or you could buy a used one out of a salvage yard or from on e-bay etc....

Boy your way off base . All the gauges are inputs from the ECM - engine computer . The VSS - vehicle speed sensor , ETC - engine coolant temp sensor , sending unit in the fuel tank , All this sensors input the engine computer . The PCM then sends this info on the GMLAN serial data bus ,communications network . The Instrument cluster has a microprocessor inside that translates this info an controls the gauges. You probably have an instrument cluster problem or a communication network problem . Your best bet is to take your vehicle to the dealer or some other qualified repair shop. Need to have it checked for DTC'S - diagnostic trouble codes.
Indicators and Warning Messages
Refer to Indicator/Warning Message Description and Operation.
Engine Coolant Temperature Gage
The instrument panel cluster (IPC) displays the engine coolant temperature as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the engine coolant temperature. The IPC receives the coolant temperature information via serial data message from the body control module (BCM). The engine coolant temperature gage defaults to 60?°C (140?°F) or below if:
?€¢
The ECM detects a malfunction in the engine coolant temperature sensor circuit.

?€¢
The IPC detects a loss of serial data communications with the ECM.

?€¢
The IPC detects a loss of serial data communications with the BCM.
Fuel Gage
The instrument panel cluster (IPC) displays the fuel level as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the fuel level percent. The body control module (BCM) sends the fuel level information from the ECM to the IPC via a serial data message indicating the fuel level percent. The fuel gage defaults to empty if:
?€¢
The ECM detects a malfunction in the fuel level sensor circuit.

?€¢
The IPC detects a loss of serial data communications with the ECM.

?€¢
The IPC detects a loss of serial data communications with the BCM.
When the fuel level is less than a pre-determined value, the low fuel indicator illuminates in the IPC.
Odometer
The vehicle odometer is calculated and stored electronically in the instrument panel cluster (IPC). The IPC contains a season odometer and trip odometer A or B. Momentarily press the trip/fuel button in order to toggle between the season odometer and the trip odometer. Press the set/reset button for greater than 0.25 seconds, while the trip odometer is displayed, in order to reset the trip odometer. The IPC displays the vehicle mileage and trip mileage as determined by the engine control module (ECM). The IPC calculates the mileage based on the serial data vehicle speed information from the ECM. The odometer will display 'error' if an internal IPC memory failure is detected. The odometer displays either miles or kilometers and can be set through the customization menu in the driver information center (DIC).
PRNDL Display
The instrument panel cluster (IPC) displays the selected gear position as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the gear position. The PRNDL display blanks if:
?€¢
The ECM detects a malfunction in the transmission range switch circuit.

?€¢
The IPC detects a loss of serial data communications with the ECM.

?€¢
The IPC detects a loss of serial data communications with the body control module (BCM).
Speedometer
The instrument panel cluster (IPC) displays the vehicle speed as determined by the engine control module (ECM). The IPC calculates the mileage based on serial data vehicle speed information from the ECM. The IPC receives vehicle speed information from the body control module (BCM) via a serial data message. The speedometer defaults to 0 km/h (0 mph) if the IPC detects a loss of serial data communications with the ECM or BCM.
Tachometer
The instrument panel cluster (IPC) displays the engine speed as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the engine speed. The IPC receives the engine speed information from the body control module (BCM) via a serial data message. The tachometer will default to 0 RPM if:
?€¢
The ECM detects a malfunction in the engine speed sensor circuit.

?€¢
The IPC detects a loss of serial data communications with the ECM.

?€¢
The IPC detects a loss of serial data communications with the BCM.

How to Diagnose Controller Area Network CAN Suggest you read up on C.A.N.

The gauge in the instrument cluster could be going bad ! maybe. Is that what your going by ? You need to have it hooked up to a scan tool ,not a code reader . It will tell what the ECT - engine coolant temperature sensor is reporting to the PCM - engine computer .The PCM turns on the cooling fans when the temp. reaches 262 degrees ! Are the cooling fans coming on ? Thermostat sticking ! Go to harbor freight an buy a Laser Temp Gun Infrared Thermometer , $30.00 . point it at the upper radiator hose an see what the actual temp is !
Engine Coolant Indicators
TEMP ?€¢
The instrument panel cluster (IPC) illuminates the TEMP indicator when the powertrain control module (PCM) determines that the coolant temperature is more than 128?°C (262?°F). The IPC receives a discrete input from the PCM requesting illumination.

?€¢
The IPC performs the display test at the start of each ignition cycle. The IPC illuminates the TEMP indicator.

Is the cooling system full of coolant ?
The instrument panel cluster (IPC) displays the engine coolant temperature as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the engine coolant temperature. The IPC receives the coolant temperature information via serial data message from the body control module (BCM). The engine coolant temperature gage defaults to 60?°C (140?°F) or below if:
?€¢
The ECM detects a malfunction in the engine coolant temperature sensor circuit.

?€¢
The IPC detects a loss of serial data communications with the ECM.

?€¢
The IPC detects a loss of serial data communications with the BCM


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