94 Volvo 850 T5 - Fluctuating temperature gauge

Post by **Volvofan94** » 10 Sep 2015, 22:31

Hello Guys,

The issue started this past weekend when I took the car on 4 hour round trip on the interstate. On the way back I notice the temperature gauge bounce from normal temp down to the cold mark then back to normal. Or sometimes it dropped halfway between normal and cold before returning back to normal. The gauge would repeat the process roughly 5 times until I arrived at my destination. No CELs appeared so I kept on the interstate and made it there without issue.

Later in the week the car gave error code 123 for the ECT signal. I presumed the ECT may have been causing the issue over the weekend and a new one should arrive tomorrow. Today the engine surges a little while driving and the temperature gauge goes up and down more frequently than it did over the weekend. I've tried unplugging the ECT and plugging it back in, but no success.

The current ECT is an OEM Volvo unit replaced about 2 years ago. Thermostat was replaced at about the same time with a Wahler OEM brand. Within the last two weeks the coolant supply and return hoses for the turbo were replaced.

Has anyone experienced this issue before and replacing the ECT fixed it?

Thank you!
-volvofan94

Post by **erikv11** » 11 Sep 2015, 16:06

I am curious to know how it turns out. I would also suspect the ECT sensor but to answer your question: nope, haven't seen this one myself.

Post by **Volvofan94** » 11 Sep 2015, 23:40

Today the car has gotten much worse. It'll now suddenly rev up to 4,000 RPM when at a stoplight or driving. It holds 4,000 RPM until I turn the engine off. I keep a hand close by the shifter to move it into neutral in case the RPMs increase.

The ECT didn't arrive today; I'm waiting until next early week now. I'll keep updating the thread on progress, but I'm beginning to think it may be something more than the ECT causing the issue.

-volvofan94

Post by **abscate** » 12 Sep 2015, 03:31

Definitely more than just ECT.

Inspect throttle cable and cruise linkage for binding
Inspect throttle body for cleaning and smooth operation of the throttle plate - I bet that is it binding on dirt.
IAC valve sticking wide open?? Although - I don't think this will give you 4000 rpm

There are links/threads on the exact resistance measurements of the ECT with temperature.

Post by **misha** » 12 Sep 2015, 17:54

Oem ect rarely fails,especially if it's only 2 years old.
Mine is still original and no problem with it.

Check connector for it.Check for corossion and clean it up if there is any.
You should know that you can ONLY use oem ect or at least Vernet.Other aftermarket brands simply don't work on these cars.

Post by **Volvofan94** » 13 Sep 2015, 11:58

We may be able to call this thread solved. This morning I checked the ECT connector per misha's suggestion. I think one or both of the terminals inside the plug weren't making good connection causing the erratic engine behavior and the 123 error code. I cleaned the connectors, reshaped them just enough to make a good connection to the ECT, and plugged everything back in. Took the car for a test drive and the temp needle stayed at 3 'o clock the whole time.

I'll report back if the issue returns, but at least now I have a replacement ECT sensor in the garage.

Thanks all!

Post by **abscate** » 14 Sep 2015, 02:27

Did it solve both the temp gauge issue and the 4000 rpm race?

You learn something new every day!!