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Old 05-10-2020, 01:09 PM   #1
Joedoak
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Default Engine Coolant Temp (ECT) Sending Unit Issue

Coming to the OGs (no Facebook) for this one:

Due to COVID, my '92 LS sat for 6 weeks without moving/starting. Upon starting I had two issues:

1) a totally dead battery that has since been replaced; and,
2) My coolant gauge is going all over the place with no rhyme or reason to it

At first, when I would start the car, the temp needle would immediately go to normal operating temp and then rise to at/near H within a few minutes. Way too fast for a warm up. Not possible. The car is NOT overheating, though. I drove the car around for nearly 30 minutes and noticed zero evidence over heating, i.e. fans working fine, lower hose hot, not loss of coolant or additional coolant in the overflow reservoir. Also, car was driving completely normal.

So, I simply replaced the ECT unit on the water passage with a brand new one. I tested the old one and the brand new one and they both are within spec, so working fine. Upon starting the car with the new ECT unit, the temp gauge acted normal at first, staying pinned at L, but then after a minute or so, it started rapidly rising. It goes to normal operating temp and sits there for about 3 minutes, upon which it starts to rise and sits just below H. Again, the car is NOT overheating. Fans are on, no issues with the overflow, etc. Drove around, car runs fine. No performance issues.

So, next I tested the gauge using the procedure in the manual. I ran a jumper wire (grounded) with the ignition switch on and the gauge needle rose up rapidly just as the manual said it should do. So it appears the gauge is working properly.

After running the gauge test, I started the car again to see if miraculously it would work properly. Again, first minute it acted normal, then the needle quickly went to operating temp. I then turned it off and typed this.

Any thoughts guys? What am I not considering here.

Last edited by Joedoak; 05-10-2020 at 01:12 PM.
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Old 05-10-2020, 02:17 PM   #2
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There are 2 engine coolant temp sensors on the water passage. The one for the ECU is on the left ( facing the engine from the front of the car.) The one on the right is for the gauge. Which one did you replace?
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Old 05-10-2020, 02:45 PM   #3
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I replaced the one on the driver's side about an inch behind the bleeder blot. That's the one that sends info to the gauge cluster.
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Old 05-10-2020, 05:23 PM   #4
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The temp sender has a very simple female bullet connector. Ot might be loose or corroded, often if green powder exists on the connector its also goes a few inches up the wires inside the insulation. Did you tighten the screws that ground the guages in the back of the cluster? Thats another possible problem.
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Old 05-10-2020, 07:10 PM   #5
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Connector looks solid. Snug fit and I did not notice any corrosion. I had to replace the connector on my old '95 coupe, so I've faced that challenge before.

I haven't opened up the cluster.

It is a really simple system. It seems only one of three things could be causing this: 1) the sending unit (but it's new and tested good); 2) the cluster, or 3) the wiring. Note - I did run the manual recommended cluster test and it proved the cluster needle was working, though it shot up super fast and hit H.

Thoughts?

It's a real mystery that I hope to solve soon.

Last edited by Joedoak; 05-10-2020 at 07:24 PM.
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Old 05-10-2020, 07:54 PM   #6
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I should also mention that upon first starting the car after the 6 week hiatus, CEL was on and D4 was flashing. I turned the car off and the CEL and D4 were off. They have come on a couple more times over the past few weeks, but each time I try to pull the code, there is nothing stored to display. No flashing of the CEL, so I have no clue what it was trying to tell me.
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Old 05-19-2020, 10:03 PM   #7
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Hmm my initial first thought was the cluster ground wire was damaged as it'll give an immediate hot indication. Your mysterious CEL codes have me wondering if you had water get in on the passenger side floorboard check to make sure the ECU didn't get a bit moist.
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Old 05-19-2020, 11:53 PM   #8
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Not the ground wire. It doesn’t immediately go to H. Start. Needle sits at C for 90 seconds, then it moves to operating in about 5-10 seconds. Stays there for 5 minutes, then moves up to just below H. Every time.

No water on the passenger side floor board.
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Old 05-20-2020, 12:50 PM   #9
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Okay well then you pretty much have a typical Acura Legend nut busting, smile from God needed lurking mystery issue. I'm betting you know those come with the territory on these cars. Well you mentioned THREE possibilities and you seem to have ruled out TWO of them (confirmed good sending unit and good gauge in the cluster) which would lead to unfortunately the most DIFFICULT of the three to find and correct ... wiring. Sadly with the age of these cars wiring "anomalies" are going to become more and more prevalent. I won't even talk about what my sedan enjoys doing these days.
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Old 05-23-2020, 02:56 PM   #10
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If you look at page 23-142 of the G2 manual available on this site, the coolant gauge circuit is fairly simple. There is voltage going to the gauge, a ground, and a wire going to
the temperature sensor for the gauge. It shouldn't be hard to check for voltage, ground, and continuity to the temperature sensor. The temperature sensor can be checked by measuring the resistance at several temperatures (such as ice water and boiling water). The gauge could be checked by substituting various resisters for the temperature sensor.

The symptoms of a check engine light and D4 flashing sound like the other temperature sensor that goes to the ECM. I'm wondering if some how those sensors have gotten mixed up though as I remember the one that goes to the gauge is a single pin connector and the other is a two pin connector.
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