Engine Coolant & Oil Temp & Pressure Swiches, Sensors, & Sending Units Explained

INFORMATION Articles / Teg Tips
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[SIZE=“3”]OK, I’m sick and tired of answering this question. It’s been an issue many of us have dealt with and many more will in the future. The info is already out there if you search, but still it seems people can’t figure this out. So i’m gonna type it all out once and for all. From here on out I’m not responding to any threads regarding this issue. All questions regarding the location or wiring of these should be posted in this thread only![/SIZE]

[SIZE=“3”]DISCLAIMER[/SIZE]

  1. All of this info is to the best of my knowledge and has been backed up by many sources. But I’m not taking responsibility for anything you do to yourself or your vehicle. Use good judgment and always double check everything.

[SIZE=“3”]NOTES[/SIZE]

  1. I will use standard wiring color notation. e.g. red/wht = red insulation with a white stripe.
  2. Wire colors may differ from model to model and car to car. The colors listed here are from personal experience and wiring diagrams in the helms.
  3. Colors of sensors, sending units, switches and their connectors may differ from model to model and car to car.
  4. The terms “sensor”, “sending unit”, and “switch” are NOT interchangeable. Read carefully, type carefully.
  5. I may, on occasion, use the term “unit” to refer to any of the above sensors, sending units, or switches. e.g. “You will find three ‘units’ on the back of the block.”
  6. ECT = Engine Coolant Temperature. It doe NOT refer to any specific part.

OK, now onto the meat and potatoes!

[SIZE=“4”]ECT Switch[/SIZE]

Wire Color(s):
BLK
YEL/GRN

Location:
Located on the back of the block (to the left of the oil filter) on OBD0 b series engines. Located on the thermostat housing on 92+ b series engines. It should be noted that the ones on the back of the block look completely different from the thermostat housing mounted switches.

Purpose:
Tells the radiator fan to turn on once the coolant temp is above a specified temp.

Details:

  1. This is a ground switch. BLK wire leads directly to ground.

  2. YEL/GRN wire leads directly to the radiator fan motor on models w/o AC. YEL/GRN wire leads to the radiator fan relay on AC equipped models.

  3. Continuity between terminals (radiator fan is told to turn on) when the coolant temp is above 196-203 deg F.

  4. The 89-91 style switch is strange looking, like it’s made from green epoxy with two pins sticking out. Each of these pins is similar in shape and size to a headphone jack. A single wire connector connects independently to each of these pins. The whole unit is then covered by a black plastic/rubber “boot” in the shape of a hershey kiss. On 89-91 blocks there are THREE units to the left of the oil filter. The ECT switch is the highest up unit (see mrpenny’s picture below)

  5. The 92+ style switch is a more standard shaped two pin connector. The switch is commonly brown and the connector gray in color.

[SIZE=“4”]ECT Sensor[/SIZE]

Wire Color(s):
GRN/WHT
RED/WHT

Location:
Located on the distributor side of the cylinder head. Position is slightly different between vtec and non-vtec heads due to the addition of the vtec solenoid.

Purpose:
Gives the ECU information regarding coolant temp.

Details:

  1. This sensor is a standard shaped two pin connector. The switch is commonly white and the connector gray or cream in color.

[SIZE=“4”]ECT Sending Unit[/SIZE]

Wire Color(s):
YEL/GRN

Location:
Located on the distributor side of the cylinder head.

Purpose:
To tell the temp gauge in you gauge cluster the temp of the coolant.

Details:

  1. This sending unit is a small unit with a single pin connector protruding. This pin is similar in shape and size to a headphone jack.

[SIZE=“4”]Engine Oil Temperature Switch[/SIZE]

Wire Color(s):
BLK
WHT/GRN

Location:
Located on the back of the block, to the left of the oil filter.

Purpose:
Tells the radiator fan to turn on if the engine is off and the oil temp is above a certain temp.

Details:

  1. This switch is only found on US spec DA’s with A/C. There may be more exceptions to this rule but info is sparse. According to the Helms it is not used on DA’s w/o A/C or Canadian DA’s. And many imported motors do not have this switch. I can’t speak for other years or models.

  2. Continuity between terminals (radiator fan is told to turn on) when the oil temp is above 221-232 deg F

  3. This is a ground switch. BLK wire leads directly to ground.

  4. WHT/GRN wire leads to the Radiator Fan Control Module

  5. This switch is a standard shaped two pin connector. The switch is commonly green and the connector green in color. On 89-91 blocks there are THREE units to the left of the oil filter. The Engine Oil Temp Switch is the most leftward unit - furthest from the oil filter. (see mrpenny’s picture below)

[SIZE=“4”]Engine Oil Pressure Switch[/SIZE]

Wire Color(s):
Yel/Red

Location:
Located on the back of the block, to the left of the oil filter.

Purpose:
This switch is for your oil pressure warning light.

Details:

  1. This is a single pin switch, it looks sort of like a headphone jack (male).

  2. On 89-91 blocks there are THREE units to the left of the oil filter. The Engine Oil Pressure Switch is the bottom most rightward unit - closest to the oil filter. (see mrpenny’s picture below)

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above post is incomplete, just posting to save my progress, i will update as i have time. please refrain from posting any questions till i finish.

[SIZE=“5”]if anyone has pics to contribute (especially of the obd0 ect switch) please EMAIL them to me. thank you.[/SIZE]

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wow. just now saw this. sorry that i can’t figure this out on my own. all shame on me…

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Here’s my contribution:
The one with the black boot is the ECT swtich, the green connector is the oil temp sensor, and the one prong connector is Oil pressure switch. So it goes from top to bottom: ECT switch, Oil temp switch (green connector), and then oil pressure switch
I’m pointing at the ECT switch here. This is the back of a 90-91 block

a79128d0-1.jpg

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perfect, thanks mrpenny, i’ll add that to the main post when i get a chance.

gil, no worries, and sorry i couldn’t take your call last night after repeatedly telling you to call me…

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Colin here are a couple of pics.
90 DB1 factory engine.

My car has been running excessively rich and I’m getting about 19 mpg. I was thinking of swapping out the ect sensor. I went to pullapart and got me an o2 sensor and the ect sensor. I’m not throwing any codes but it is running real rich.

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^^looks like you need to replace your cam end plug.

Good info in here, going to replace my obd0 ect switch very soon.

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[QUOTE=nizzan4u2nv;2117346]^^looks like you need to replace your cam end plug.

Good info in here, going to replace my obd0 ect switch very soon.[/QUOTE]

looks more like distributor o-ring although i cant see the underside of the front-most cam seal, which prolly needs replacing too if the dist o-ring does.

e: just realized this thread is old

necro!

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Please keep this thread on-topic, you can discuss oil leaks elsewhere.

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Great info Colin. I guess I’ll be checking everything once I get a chance to. I’v been having overheating problems lately. I’m fine while I’m on the road driving but, once I’m at a stop (i.e.: the drive through at a fast food joint) my temp gauge tends to rise. Once I get back on the road again and moving, the temp goes back to normal. I’m assuming it’s my fan or lack there of. I’ll find out I guess. Once again, great info Colin. :up:

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Yeah, that sounds like a fan issue but could be a thermostat or radiator issue as well. Shouldn’t have anything to do with the units I described above. The ECT switch could be a possible culprit (not telling the fan to turn on) however they don’t fail very often, so I would start troubleshooting down other avenues first, if everything else is OK that’ll lead you down the path to your ECT switch while troubleshooting your fan wiring.

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I swapped out my 1991 b18a1 for a 1996 b20b, so the ECT switch will now be on the thermostat housing and there is no longer an Oil temp switch. I used my b18a1 harness on the new motor.

My question is…how do I wire my b18a1 harness up to the new ECT switch? The wire colors aren’t the same, luckily the switch on the new motor came with a plug and barely enough wire to work with. Because it is a ground switch, does it matter what wire goes where? And instead of extending the b18a1 ECT switch wiring to reach the new switch location, can I open up the harness near the switch and pull the wiring out there?

Also, what should I do with my b18a1 oil temp switch wiring? I’m a bit concerned about just leaving it hanging back there, since there’s nothing to plug it in to on the new motor.

That description matches the ECT switch on my 90-91, may want to fix the years you listed.

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DOHC, Thanks for catching that year mistake, I must have been thinking civics for some reason! It’s fixed now.

Wire color doesn’t much matter, as long as the wires are connected properly. And in this case it doesn’t matter, you can actually wire it either way and it should work. The ECT switch is just that, a switch, it provides continuity between the two wires plugged into the switch. So it doesn’t matter if your ground is hooked up to terminal A and your fan to terminal B, or vice versa. However I personally would match it up and wire it according to the stock wiring colors, just cause I’m anal like that.

Cutting a hole in your harness and pulling the ECT switch wires out is going to be hard, however I don’t like extending that wire either. I would use an exacto knife to cut the electrical tape on the loom which runs from where your ECT switch wires enter the harness on the back of the block, to where you want it to exit, but the Thermostat housing. Remove the electrical tape, split the loom and find your ECT switch wires and pull them over so they come out near the harness junction right by your Thermostat housing. Put the loom back on the rest of the wires and re-tape. It’s really easy, just take your time.

You can just take your EOT switch and just tape off the connectors, of if you’re splitting your loom to move your ECT switch wiring you can clip the wires and tuck them into the loom so nothing is dangling. You don’t really need the EOT switch, if your engine has one and you have a/c I’d use it. If your engine doesn’t have one or if you don’t have a/c, then I wouldn’t bother.

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Thanks for the reply, I’ll try that stuff out this wednesday when I finish the swap and let you know how it worked out. :rockon:

Figured I’d contribute some pics of the sensors on my 1996 jdm b20b(low-compression, p75 cylinder head/p75 intake manifold version). I think it would be the same as the late model 2nd gens, 3rd gens, etc.

ECT switch-

ECT switch plug-

Oil pressure sensor, no ECT or oil temp switch-

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I split the loom like you had suggested, wasn’t hard at all. I pulled the ECT switch wiring back and shortened it, then I used the plug + pigtail I cut off the oil temp wiring for the ECT switch…direct fit. Re-loomed/taped everything after tucking away the oil temp wiring, and it looks better than new! :rockon:

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:up: Nice work! I like wiring engines, nothing fancy like those tuck harnesses, just customizing it the way I want. I re-did my whole engine harness this past year, moved some wires, changed some stuff around, all new tape and heatshrink. Looks nice now :slight_smile:

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I should be good then if my new engine doesn’t have the EOT switch but i am still running a/c.

[QUOTE=DOHCIntegraLS;2118236]
Figured I’d contribute some pics of the sensors on my 1996 jdm b20b(low-compression, p75 cylinder head/p75 intake manifold version). I think it would be the same as the late model 2nd gens, 3rd gens, etc.

ECT switch-

ECT switch plug-

Oil pressure sensor, no ECT or oil temp switch-
[/QUOTE]

could you please host these on g2ic so the class can see them? i’m curious and the pics don’t work for me.

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i too would like those pics rehosted.

after three weekends ive finally gotten my B18 out and i too was taken aback by the lack of these sensors on my B20.

i guess ill use this opportunity to rewire my bay as well while i wait for the pics.
isnt there a thread that we can link this thread to that neil will fix the images?

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It looks as if someone edited my links, this has happened to several of my posts and I don’t know why. I keep having to edit the posts to fix the links.

Anyways, fixed the links and pics are now working again.

If you’re going from a b18a1 to an early model low-compression b20b like I did, check out the guide I just typed up…

http://www.g2ic.com/forums/showthread.php?t=203192

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will you have a check engine light for no oil temp switch?