• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

940 Issue with Aftermarket Coolant Temperature Sensor

iamrolling

New member
Joined
Nov 5, 2019
I shotgun replaced my coolant temperature sensor trying to stop the car from dumping so much fuel into the engine. I know, I should have tested it. But it cost next to nothing, and is one of those SU-5817s sold by AutoZone. I assumed it would work adequately and fit well.
It did work, and the exhaust smells much better. And I got it the old one out and new one in with much less trouble than expected. I removed nothing. Just stuck a 19mm deep well 12 point bolt rounder in there on a 3/8 ratchet, done in under 10 minutes.
The problems happened trying to plug it in. I push the connector onto the sensor, and the clip never retracted. You could just pull the harness connector right off with a slight tug. How did they screw up an EV1 connector so bad?
Not wanting to drain the coolant again, I went about modifying it in place. With a series of small files and razor blades, I shaved a bit off the end of the sensor's connector plastic and also the flat side of the tabs. I also removed the rubber rectangle from the bottom of the harness connector. After a painful hour, it finally clicked into place. Once again, I learned that I should have spent the extra few bucks for a Bosch part.
I can probably shave down the side tabs a bit more and fit the rubber piece back in, but that's where I have questions. Should I even put that thing back in? It's definitely failed, because the harness terminals were corroded when I found them. Is it possible to buy new ones that aren't so hardened? Could I just lightly paint the bottom of the connector with an RTV silicone, or would that cause other issues in the future?
 
Even after you change the temp sensor again. I would spend a bit of time with a meter and make sure the signal getting to the computer is proper. Testing done at the computer connection verifies the wiring and that the impedance values on the sensor are correct. Lots of threads on testing the coolant temp sensor.
 
Replacing the connector might not be a bad idea, now that I've seen the shiny metal on Barton's terminals. Mine sure don't look like that.
I wanted to test it, but I'm having trouble finding a multimeter in my price range that I like. Advance Auto's looks the same as the Harbor Freight meter with a nicer color scheme and a 400% markup, and AutoZone's looks more like what I want but has the leads permanently attached to the sides Famicom style. And after breaking 4 or 5 of the Harbor Freight meters by looking at them wrong, I'm sick of buying them. I'm not unhappy that replacing the part fixed multiple things, but I know I should have taken the time to get a clearer picture of what happened.
 
This little guy has been kicking around in the back of my car for 5 years and still works:

https://www.amazon.com/gp/product/B00KHP6EIK/

Fluke will be better but if you want something you don't have to care about, $12 is pretty good. Sounds like from reviews that some of them are DOA though.
Looks like a copy of the Actron CP7400 or 7665. I'll go with something like this. It should do better than the Harbor Freight DT830 clone, which is usually missing a lead and a few display segments after 5 months in the back of my car.
 
I have an Actron CP7665 coming to me soon, so I'll be able to test the connection. If anyone's looking for a good cheap multimeter, you can get the Actron CP7665 for a few bucks more than a DT830 right now. And Actron products are blessed by Bosch USA. There's even a picture of a coolant sensor in the instruction manual with an almost-EV1 connector. There's also a Bosch branded FIX 7665, but the only difference is it has a black housing instead of a conspicuous Goku shirt color scheme.

Now what about cleaning oxidized contacts? The CRC and WD40 contact cleaners that I can find locally don't say anything about removing corrosion.
 
I'm straying from my own topic, I know, but this might be interesting. I found out that the MSR-R500 and the 7665 are derived from the Uni-Trend UT33D and UT33C. There are other variations of the UT33 series, with the only difference being the color scheme and branding.

Both UT33s are 2000 count meters, but the UT33D has more features and better protection. In hindsight, I should have gone with the MSR-R500. But the Actron unit looks so much easier to find in a pile of red and black tools. And the risk of frying it on anything in a combustion engine car is minimal anyway.

On the DT830 meters, all are based on the same Intersil ICL7106 chip with any number of features connected. Many have no fuse at all.
The UT33 meters are cheap enough at this point that they've superseded the DT830 series. Unless you have a free multimeter coupon from Harbor Freight, at least. But after you rip the leads off or break the screen, don't pay more than $20 for a UT33 no matter how much you like the color scheme of that particular model. Or pay little enough that you end up with a cut down version made with cheaper parts.
 
Last edited:
Got my Actron CP7665. It's very much a UT33 with different colored plastic. It even has a spacing error cast into the warning on the back of the case and a QCPASS sticker that inspires no confidence. But it came with some nice leads and has a ceramic fuse, and it doesn't glitch out when you squeeze the casing like I've seen in the reviews for some other rebranded UT33s. And it came with a soft cover instruction manual. I still feel bad for anyone who paid the full MSRP of $50.

I got to measure the sensor at the ECU, though. Here are the results:
Ambient temperature (80F): 1780 ohms
Temp gauge centered: 180 ohms

I can't say for sure that the meter is completely accurate and don't know what the numbers are supposed to be on the completely unlabeled coolant temp gauge, but the trend looks about correct.
 
Last edited:
what color is the plastic on this sensor? Are you sure you weren't trying to plug on the connector upside down? Also, the part number you posted may be wrong part for a 940. LH2.2 and LH2.4 sensors are not electrically interchangeable even though the connector is the same. And yes, I have seen aftermarket LH2.2 sensors with the black plastic.

20C (68F) should be about 2500 ohms for the LH2.2 sensor. The LH2.4 should be half that IIRC. The LH2.4 sensor has 2 circuits which uses the head for the ground. The LH2.2 sensor has 1 circuit with a ground wire.
 
Last edited:
Black plastic. And no, I'm sure it was just a bad casting. According to VOC:
ECT resistance cold for LH2.4 systems should be around 6k ohms at 32 degrees F (0 deg C), 2300-2700 ohms at 68 degrees F (20 C), and 200 at 212 F (100 C).
I'm aware of the internal difference in the 2.2 and 2.4 sensors. But the 2.2 sensor has a teal plastic EV1, doesn't it?

Later today I can test each terminal of the ECT against ground. If one of them shows a zero, I'll know for sure. Both eBay and AutoZone's systems insist that the SU-5817 is incompatible with 2.2 cars, but we'll see. They have been wrong before.
 
Last edited:
At 77F, 1860 out of the first terminal then 1890 out of the other. No zeroes. But from a look at Rockauto's selection, there definitely are 2.2 coolant sensors with black plastic, and a 2.4 sensor with teal plastic. There was even one with white plastic.
 
Back
Top