99 V70 P0118 -- ECT Circuit High Input

Post by **E Showell** » 23 Feb 2014, 11:25

I have a P0118 on my wife's '99 V70. Looks like I'll be swapping the ECT and thermostat. I feel like I've been going through ECTs like popcorn of late.

I bet I've changed four on two cars in the past six years. Is this level of failure expected/understandable, or perhaps symptoms of some perhaps larger lurking problem (or is parts quality simply that bad). I've been changing stuff out with genuine Volvo parts as well.

Anybody else running through ECTs lately?

Post by **jreed** » 23 Feb 2014, 14:28

Funny you should mention it... I just finished replacing my old FAE ECT and Wahler 90C thermostat for a new Volvo SWF ECT and Volvo/Wahler 90C thermostat. I'm going to try to measure the old ECT and see if it's in spec.
The build quality on the FAE is definitely lower quality compared to the SWF. The SWF has a tapered self-centering collar at the base to ensure a good seal. The wire gauge is also thicker on the SWF.

: New Volvo OEM SWF (front) and old aftermarket FAE (back) engine coolant temperature sensors

Post by **jreed** » 24 Feb 2014, 16:35

The old FAE ECT measures high for resistance. I measured it at a few temperatures using a couple of ohmeters. Results below:

: FAE ECT reads high resistance compared to the Alldata specification; ECT temp FAE versus Alldata.png (86.45 KiB) Viewed 3465 times

The dashboard gauge is now reading at the midpoint with the new SWF ECT installed.

Post by **E Showell** » 25 Feb 2014, 12:34

Hate to admit the graph means nothing to me.

Post by **jreed** » 26 Feb 2014, 04:40

No problem. The graph is mainly showing that the old FAE sensor, while giving a more or less linear response (when plotted on log scale), is reading resistance values that are all shifted higher than they should be at any given temperature.
For example, at about 360K (about 87C or 188F), the ECT should be reading about 200 Ohms, but instead it's reading about 300 Ohms, which gives a falsely high resistance reading, leading the computer to think that the engine coolant is colder than it really is.

Why is the sensor reading high? I don't know. Inspecting the old part more closely, I found a failed seal between the epoxy and the metal where the wires enter the top of the sensor (red arrow below). This crack might have allowed water to enter the sensor and change it's resistance -- but I'm not sure.

: Old FAE ECT sensor (left) has a cracked seal at the epoxy-metal interface. New SWF/OEM sensor on right has a plastic collar between the epoxy and metal.; Cracked seal on FAE ECT labeled.jpg (139.41 KiB) Viewed 3452 times

Interestingly, the new Volvo SWF OEM sensor has a two part seal with a plastic collar between the epoxy and the metal. Maybe the plastic collar absorbs the expansion and contraction of the materials and helps avoid cracking.

Post by **abscate** » 26 Feb 2014, 05:19

E Showell wrote:Hate to admit the graph means nothing to me.

It doesn't matter. It's beautiful. I'll use it next meeting to tell Finance why bonuses have to go up 8.50 percent next Q. "I can have Engineering come in an explain " will scare them off.

Note the the resistance scale on the ordinate is logarithmic...this means that the small changes in position up down are huge changes in actual resistance.

Post by **jreed** » 28 Feb 2014, 04:55

Just wanted to add a couple of images of useful tools / approaches to replacing the ECT and thermostat. I had good luck with an inexpensive long Torx key on the two T-40 bolts that hold the thermostat cover in place. The long key is needed to clear the fuel lines and come in perpendicular to the back bolt -- this helps to avoid stripping the head on the bolt.

: Long Torx-40 key makes it easy to loosen back bolt

To remove and install the ECT, I used an open ended 19mm wrench from the top. You may have to flip the wrench over to adjust the angle in order to fit onto the head of the ECT.

: 19mm open ended wrench from the top to tighten up the ECT.

Good luck!

Post by **abscate** » 28 Feb 2014, 05:04

If your thermostat screw heads look rusty or worn, buy two new ones with your thermostat so that they won't strip on you.

Post by **E Showell** » 28 Feb 2014, 05:25

I just did a replace on the '98 V70 within the last few weeks. I've looked at the electrical connectors for the '99 which is different and can't see the trick to releasing it. I am familiar with all the other quirks of this job as far as tools and clearances go but the pics will undoubtedly help someone, so thanks for those.

Post by **E Showell** » 03 Mar 2014, 07:06

Well, knock me over with a feather . . . the clip simply pulled apart. No magic tricks or incantations to separate the parts. There is a clip looking side to the replacement sensor (it was on the original as well) but it does not appear to have any function.

Replacement was simple and no stripped bolts due to liberal PB Blaster application a few hours before undertaking the job.

Soup to nuts in a leisurely twenty minutes and that's because I drain the coolant expansion tank with a turkey baster rather than put the car up on ramps and drain the coolant from the radiator.