940 Celebration temp gauge

[Forrest]

I doubt this would work how you think it might. The gauge uses a circuit to measure the resistance across the temperature sender whose resistance decreases as the temperature increases. I don’t know for certain, but I expect this means the gauge is actually an ammeter which measures the current flowing through the closed circuit. Feeding it a voltage from an external source without a resistor in the circuit will either destroy it or have no effect. Neither will help you isolate the existing fault.

Why don’t you just short the two wires at the sender with a paper clip and see if the gauge moves when you switch the ignition to position 2? Assuming it does you can then focus on whether it’s your thermostat or temperature sender that is faulty.

[940volvoman]

Thanks, Forrest,
I'll follow tour suggestion and let you know.

[Laird Scooby]

Originally Posted by 940volvoman

Since posting my temp gauge problem I haven't had time to follow up.
However it doesn't mean I haven't been thinking about it. I've come up with an idea which may help trace the fault(to the gauge, at least. I have a 12 volt adjustable transformer, which I thought would gradually increase the voltage to the gauge,with the view to protecting the gauge and any other sensitive electronics on the dash.
What do you think?

You will end up creating at least one very strange smell, at least one horrible mess and have no instrument cluster left!

Originally Posted by Forrest

I doubt this would work how you think it might. The gauge uses a circuit to measure the resistance across the temperature sender whose resistance decreases as the temperature increases. I don’t know for certain, but I expect this means the gauge is actually an ammeter which measures the current flowing through the closed circuit. Feeding it a voltage from an external source without a resistor in the circuit will either destroy it or have no effect. Neither will help you isolate the existing fault.

Why don’t you just short the two wires at the sender with a paper clip and see if the gauge moves when you switch the ignition to position 2? Assuming it does you can then focus on whether it’s your thermostat or temperature sender that is faulty.

Spot on except for a couple of minor points. The guage is actually a constant current source and measures the voltage developed across the sensor by its varying resistance. Because the sensor is NTC (resistance goes down as temperature goes up) it does some clever jiggery-pokery to alter this voltage so it displays on the actual meter as higher when the resistance is lower (hotter engine) and lower when the engine is cold.

This is why a poor connection between the sensor and guage can sometimes result in the guage reading about halfway as soon as the ignition is turned on, regardless of engine temperature and tapping the dash often cures this temporarily.

The other thing is using a 12V transformer will give 12VAC output. Except for the alternator, there are no AC devices on the car and that has a built in rectifier to give DC out.
Just because the battery on a car is 12VDC, doesn't mean everything else on the car relies on that same voltage though - the instruments are one such item that use much lower voltages and different methods to many other manufacturers to display the parameter being measured, even if the method of display is similar.

[940volvoman]

Ive finally had time to follow up with the suggested tests, and here is what I found:

With the ignition OFF, I set the meter to ohms settings, touched one lead to ground, and the other to each terminal of the sender. No reading on the meter, at all. The engine is warm.

I then shorted across the two wires with the equivalent of a paper clip,switched the ignition on,and the gauge in the dash instantly went to 'hot'

I'm assuming that the sender is faulty.....?

[Laird Scooby]

Originally Posted by 940volvoman

Ive finally had time to follow up with the suggested tests, and here is what I found:

With the ignition OFF, I set the meter to ohms settings, touched one lead to ground, and the other to each terminal of the sender. No reading on the meter, at all. The engine is warm.

I then shorted across the two wires with the equivalent of a paper clip,switched the ignition on,and the gauge in the dash instantly went to 'hot'

I'm assuming that the sender is faulty.....?

Certainly sounds that way! Make sure when you order a replacement you order one for the guage and not for the ECU/fuel control.

[Ian21401]

Originally Posted by Laird Scooby

Certainly sounds that way! Make sure when you order a replacement you order one for the guage and not for the ECU/fuel control.

Agreed Dave re the correct sensor. Back in 2008 when I was trying to locate
the cause of the engine pulsing irregularly an ex Volvo mechanic suggested it may be the ECU coolant sensor. (It was eventually traced to a failing MAF.). But when I tried to order one from my dealer they couldn’t decide which was which and actually ordered the wrong one. ie the gauge sensor. It didn’t get fitted and lives in the spares store.
At that time I was advised that the part nos. were:
The front one, Gauge sensor VO1362645,
The rear one, ECU sensor VO1346030. (posssibly Bosch 0280130032 but not certain.

[Laird Scooby]

Originally Posted by Ian21401

Agreed Dave re the correct sensor. Back in 2008 when I was trying to locate
the cause of the engine pulsing irregularly an ex Volvo mechanic suggested it may be the ECU coolant sensor. (It was eventually traced to a failing MAF.). But when I tried to order one from my dealer they couldn’t decide which was which and actually ordered the wrong one. ie the gauge sensor. It didn’t get fitted and lives in the spares store.
At that time I was advised that the part nos. were:
The front one, Gauge sensor VO1362645,
The rear one, ECU sensor VO1346030. (posssibly Bosch 0280130032 but not certain.

Thanks for the reminder on the P/No Ian, besides Bosch 0 280 130 032, sensors ending 039 and 069 (instead of 032) also work.

[940volvoman]

so for calrity, Dave are you saying that Bosch part numbers:

0280 130 032
0280 130 039 and
0280 130 069 are the same function? The gauge sensor?

[Laird Scooby]

Originally Posted by 940volvoman

so for calrity, Dave are you saying that Bosch part numbers:

0280 130 032
0280 130 039 and
0280 130 069 are the same function? The gauge sensor?

In short, yes.

Somewhere in the Data pocket it quotes all three of those as being the same but can't remember where exactly. Either way, all interchangeable.

[940volvoman]

Dave, it would seem that most of the sensors for the part numbers you gave me havethe flat style of pins, rather than the round pins that Volvo use( at least that what most of the images show).

I've found one at Parts Monster inside ebay.Have you or anyone else bought from them? I'm guessing that their parts are of a good quality,especially as I prefer to fit Bosch