97 850 T5 Temperature gauge works intermittently

[dcarlson12]

97 850 T5 approx 259000 km.
Intermittently the temperature gauge will just sit below the curved line of the gauge. Then all of a sudden it will work fine i.e. indicate the temperature is mid way up the gauge.

I recently the repaired the broke odometer and thus had to remove the dash and I used contact cleaner for all the connectors on the back of the gauge cluster.

The intermittent temperature gauge problem actually started before I did the work on the odometer.

I believe there is only one temperature sensor on the car i.e. the one next to the thermostat and the car runs fine and the litres per 100 km reading on the gauge goes up and down fine which makes me believe that the computer is getting a correct reading from the coolant temperature sensor and is operating as it should in closed loop.

It seems that it is likely that there is a poor connection possibly in one of the wiring harness connectors and just driving the car possibly jars it enough to make proper contact.

If this make sense, which connector should I try to access/open up and clean with contact cleaner?

Or ????

Thks,
Dwight

[mecheng]

That connector is known to get corroded, unplug it and clean it with a brass brush, spray with wd40 and apply some dielectric grease

[dcarlson12]

Hello Mecheng,
Thks for the reply.
Which connector are you referring to? The one(s) on the back of the cluster? Or one in the engine compartment?
I applied contact cleaner to the ones on the back of the instrument cluster.
If it is one(s) in the engine compartment, can you advise the location of the connector(s)?
Maybe even upload a picture showing which connector(s)? Or provide a link to a photo? Not sure if photos can be uploaded with messages on this forum....

Thks
Dwight

[polskamafia mjl]

I second that question. Are you talking about the connector at the cluster or the connector on the ECT sensor itself?

For what it's worth I have the same problem although it also extends to my tachometer. I think the issue lays in the cluster itself. I have two other cluster I need to try out but I haven't gotten around it to it yet.

[mecheng]

Hello Mecheng,
Thks for the reply.
Which connector are you referring to? The one(s) on the back of the cluster? Or one in the engine compartment?
I applied contact cleaner to the ones on the back of the instrument cluster.
If it is one(s) in the engine compartment, can you advise the location of the connector(s)?
Maybe even upload a picture showing which connector(s)? Or provide a link to a photo? Not sure if photos can be uploaded with messages on this forum....

Thks
Dwight

The one above the alternator for the ECT, I've seen them get corroded.

[dcarlson12]

Is there a way I can take a photo and upload it or email it to mecheng for he/she to mark up to show which connector?

[scot850]

Yes you can add pictures. When you go into the editor function, along the bottom are 2 boxes. Click on the Full Editor and Preview box. This will bring up the section that you can add pictures or documents files.

Down below the box again, to the left there are 2 boxes marked Options and Attachments. Click on 'Attachments' and then you can add and name the pictures.

Good Luck with that!

As the the connector in the engine compartment, on an 850 or V/S/70 up to 98 the connector is mounted on the back of the power steering pump. These connectors break down with age and the wires become brittle and can fracture as well as the internal contacts oxidising. Carefully check them out. There are also resistance values v's ambient temperatures you can use to check the ECT (engine coolant sensor) when the engine is cold to see if it is working correctly.

If you have to replace the ECT we generally only recommend Volvo OE part unless you can find the OEM part from Valmet.

Neil.

[gmh]

Found this pic online the entire sensor is circled in red (connector at bottom of circle):

coolant temp sensor connector.jpg (160.15 KiB) Viewed 2653 times

[dcarlson12]

Thanks for all the replies.

I am thinking, maybe erroneously, that the connector for the coolant temperature sensor itself is fine. My reasoning is that the car runs fine even if the coolant temperature gauge reads below the scale. i.e. I am thinking that the sensor sends the correct resistance amount to the ECU but it is a signal coming out of the ECU is only reaching the gauge intermittently.
If the coolant temperature sensor goes directly to the gauge, then it would have to send a separate signal to the ECU or am I misunderstanding what happens. i.e. would the car run fine, once warmed up, if the coolant sensor were sending a faulty or no signal to the ECU?

I have uploaded a photo where I labeled a couple of 'connectors'/wires which I believe feed into and possibly out of the ECU.
I have labeled them A and B. My thoughts are that the one labeled A is the one which is possibly corroded.
If so, is it possible to open it up and clean it with contact cleaner? Can it be opened up with the ECU 'box' in place? i.e. it looks like there is very little room to move the connector towards the front of the car when unplugged

I have not yet tried cleaning the connector which was circled in the photo which gmh uploaded. If my reasoning is wrong, then I should go ahead and do that. Either way it shouldn't hurt.
I haven't hooked up a scanner to check what temperature the ECU is receiving. I guess I should do that also. It is just difficult to do that since the problem is intermittent.

????
Thks,
Dwight

[dcarlson12]

Well I unplugged the connector for the coolant temperature sensor and cleaned with contact cleaner plugged back together and then started the car. The gauge remained below the scale on the gauge. I only watched for a few minutes while idling in the drive way. Still think it is likely a different connector.

When I drove the car yesterday, the gauge immediately registered fine at start up and remained that way for a 20 minute trip on the freeway.

Now it is back to not registering.

Are there contacts/connectors at A and B which can be cleaned?

??????

Dwight