What are all the different "water-temperature sensors"?
 

This is an attempt to explain what all the temperature sensors and fan switches are for different Honda Accords. Over the years Honda has had at least 3 or 4 different schemes for temperature measurement and for controlling the operation of the radiator fans.

I'll start with some that I'm familiar with. Others can chime in because I've never owned a 77 - 90 Accord or whatever the different older generations might be.

I'll put each type in a separate post.

Table of Contents: :cool:
1990-1997 4-cyl - post #2
1998-2002 4-cyl (USA) - post #3
2003-3004 4-cyl (USA) - post #5
2005-2007 4-cyl (USA) - post #6

4th-gen and 5th-gen
1990 to 1997 USA
4-cylinder engine

Beginning in 1993 the Europe/UK Accord 4-door was a different car, built in Swindon UK. Not sure if these sensors & systems are the same.

There's 2 fan switches and 2 coolant-temperature sensors.

Fan switch A is located in the thermostat housing. It switches the fans (both) when the engine is running. Pretty sure that works when the key is turned ON but the engine doesn't actually need to be running.

Fan switch B is located in the nozzle for the upper radiator hose, near the head. This one has authority to switch one of the fans, after the engine has been turned off. There's a timer to prevent the fan from running forever even if the switch-B is stuck.

"ECT sensor" Engine-Coolant-Temperature sensor is located roughly below the distributor. It has a plug with 2 wires. This sensor provides a coolant-temperature measurement for the ECM.

Lastly, there's another temperature sender near the ECT sensor. This one has only one wire and it provides the signal for the dashboard temperature gauge.

6th-gen
1998 to 2002 USA
4-cylinder engine

There's only one fan switch and there's 2 temperature sensors.

The fan switch is located in the thermostat housing. It has authority to switch the fans (both) only when the key is turned ON. (The engine doesn't actually have to be running.) There is no provision for the fan to run after you switch off the engine.

The ECT sensor (engine-coolant-temperature) is located below the distributor. It has a 2-wire plug. It's for the ECM/PCM.

There's also a 1-wire sender nearby, for the dashboard temperature guage.

Jim: Thank You..Great Info for the members..and Me Too! :)

7th-gen early
2003-2004 USA
4-cylinder engine

The engine-coolant temperature (ECT) sensor is located in the left end of the head (towards the left side of the car) behind the EGR valve. Follow the upper radiator hose to the engine for the general area. This sensor gives the PCM a temperature measurement and the PCM in turn drives the temperature gauge in the instrument cluster.

There is a fan-switch in the bottom tank of the radiator, towards the left side of the car. Feel around for it below the fan shroud.

7th-gen late
2005-2007 USA
4-cylinder engine

The engine-coolant temperature (ECT) sensor is located in the left end of the head (towards the left side of the car) behind the EGR valve. Follow the upper radiator hose to the engine for the general area. This sensor gives the PCM a temperature measurement and the PCM in turn drives the temperature gauge in the instrument cluster.

There is another water-temperature sensor in the bottom tank of the radiator. Same location as the fan switch in the 03-04 cars, but this is not a simple on-off switch. Temperature measurement goes to the PCM, and the PCM in turn switches the fans.

important note. I totaly agree with Jim. However, If radiator is old and crusty the sensor at bottom of radiator can give inacurate feedback causing short or long fan running times. Best way to check this is to remove the sensor, clean it and be sure thier is no build up of crusty old coolant around sensor. There must be free flow of coolant around this and all sensors. But this one in particular is at bottom of radiator and is particularly susceptible to contaminants building up around it causing resistance and faulty readings. IE. fans run at odd times, run too long or run in short intervals.

relay
 

Fans also have separate relays. The cooling fan relay for example on 90 through 93 accords is in under hood fuse box , while the condenser fan relay is mounted on drivers side inner fender just about where the power steering pump is. It has 3 parts. starting from front of car going back is a/c condensor fan relay, then a smaller diode, and lastly is the a/c clutch relay.

Great info, thanks for posting

I second ^ THIS ^ :)