Broken temp gauge... The saga continues - Alfa Romeo Forum
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(Post Link) post #1 of 15 Old 31-07-16 Thread Starter
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Broken temp gauge... The saga continues

The story so far... My temp gauge had stopped working a while ago and I assumed it was the sender. I ordered another on eBay but they sent the wrong one (2 pin not 4). Any way, after getting stuck in traffic the gauge actually moved (normally I only drive on open roads) and after posting on here it was suggested that it was probably the thermostat that had gone. I had the car booked in at Alfashop, Norwich for a cam belt and had a. new thermostat fitted and the gauge started to work albeit reading a bit low. I got another sender just to make sure but after fitting it made no difference.

All was good for a few weeks but now the gauge has stopped working again. I left the engine running for ages on the drive and still no movement on the dial. I swapped the sender back to the original and still nothing.

So... Has the thermostat gone again? If so, am I just unlucky with thermostats or is it a symptom of something else?

Have both senders decided to stop working?

Or is the gauge itself the problem this time? Is there any way I can check without removing half the dash to get to it?

Thanks in advance for any help.
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The thermostats have a tendency not to work (at least in the similar engined 147/156).
A read out of the electronic box might tell you more. Go back to Alfashop (or another Alfa specialist) to have the read out.
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You don't mention if your car is a Ph1 or PH2 as the temperature gauge circuit is a bit different.
On early 2.0 TS the sensor for the temperature gauge is not the one on the thermostat but fitted on the crank case

http://www.alfaowner.com/Forum/14103658-post11.html (Ph2 twinspark thermostat with 4 pin temp sensor and loose wires)
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Quote:
Originally Posted by Henrik_45 View Post
You don't mention if your car is a Ph1 or PH2 as the temperature gauge circuit is a bit different.
On early 2.0 TS the sensor for the temperature gauge is not the one on the thermostat but fitted on the crank case

http://www.alfaowner.com/Forum/14103658-post11.html (Ph2 twinspark thermostat with 4 pin temp sensor and loose wires)
The car is a 2001 Twinnie phase 2. The sender is on the top of the thermostat.
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Ok so it is a Ph2.
Is the fan engaged (without AC enabled) if you leave the engine idling for longer time at standstill?

Next step would be to get the engine temperature read back from the ECU. You can do this by yourself using KKL or ELM cable and MultiECUscan software
If the temperature read back is correct (approx. 80 - 90C) one part of the temperature sender has correct functionality.

If you have an ohmmeter you can measure the resistance from the sender pin connected to the White/Gray wire. Measure from pin to ground (chassis) with the plug unplugged.

If the resistance is ok, next step would be to check the wire connection from the sender to the gauge. There can sometimes be a poor connection in connector G133 or in the connector on the rear of the gauge.
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Originally Posted by Henrik_45 View Post
Ok so it is a Ph2.
Is the fan engaged (without AC enabled) if you leave the engine idling for longer time at standstill?

Next step would be to get the engine temperature read back from the ECU. You can do this by yourself using KKL or ELM cable and MultiECUscan software
If the temperature read back is correct (approx. 80 - 90C) one part of the temperature sender has correct functionality.

If you have an ohmmeter you can measure the resistance from the sender pin connected to the White/Gray wire. Measure from pin to ground (chassis) with the plug unplugged.

If the resistance is ok, next step would be to check the wire connection from the sender to the gauge. There can sometimes be a poor connection in connector G133 or in the connector on the rear of the gauge.
Thanks for the help and without wanting to sound stupid; how do I read from the ECU? What should the resistance be from the grey/white pin to ground? Where is connector G133?
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As mentioned you should use an interface cable (KKL or ELM), a laptop and software (MultiECUscan or AlfaOBD).
The 16-pin diagnostic connector is near the fusebox under the dashboard.

Regarding connector G133 it should be beneath the heater if my recollection is correct.
Do you have a copy of the Workshop manual? If not search for a link on the forum or send me a PM and I will send a link to a PDF file
In this you can find a lot of information and I can't remeber the resistance for the temperature sensor. (I think it should be 2.2kohm at 25 degC)
But it is a NTC resistor so it will have a lower resistance the higher the temperature is.
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(Post Link) post #8 of 15 Old 02-08-16 Thread Starter
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Hi,

Thanks for all the help and advice. Tried checking the resistance today at work and got nothing, just an open circuit. I'll try again tomorrow with the spare sender unit that I have and see how that pans out.
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(Post Link) post #9 of 15 Old 03-08-16 Thread Starter
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I checked both sensors again today at work, this time with the multimeter set to measure resistance. Both had a reading just below 2k ohms between Earth and the grey/white connecting. I ran the car for a bit and checked again and the resistance had changed. Just to be sure I dropped the spare in a mug of hot water. Again the resistance changed but my coffee did taste a bit funny.

So... I'm guessing it's not the sensor so what do I check next that doesn't involve taking the dash apart etc? Thanks for all the help so far and any further advice/help much appreciated. The fan seems to be kicking in OK and comes on when I unplug the sensor.
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I have got a workshop manual on CD and had a look but can't find G133 but looking at the wiring diagram, it can only be the gauge or the wires in between the sensor and the gauge so I'll have a good look at the weekend.
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You can unplug the connector from the temperature sender and measure the voltage on the White/Grey wire (with ignition on).
If you measure 0V, the wire or gauge is broken.
To have the correct function a current need to flow from the gauge through the temperature sender and as the sender have a lower resistance at higher temperature the current will increase with temperature and the needle in the gauge will indicate a higher temperature.
To see if it is the gauge or the wire you can measure the voltage at the gauge (under same condition).

The Fan is controlled by the temperature sensor connected to the Engine ECU and as the Fan is enabled, when you unplug the connector, indicates this connection is ok. The ECU will enable the fan when it doesn't have any temperature information
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(Post Link) post #12 of 15 Old 04-08-16 Thread Starter
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Thanks again Henrik... I haven't been able to check the voltage at the gauge but getting about 5.5v across the white and grey wire and earth so no broken wire so I'm guessing it could be the gauge so I need to start taking the dash apart.
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(Post Link) post #13 of 15 Old 11-08-16 Thread Starter
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Haven't had a chance to take the temp gauge etc out to check the voltage but I have noticed that the bonnet open light on the dash has stopped working (I rarely run the car with the bonnet open and I always make sure it is well and truly shut after someone told my the catch can be dodgy and the bonnet can fly open at high speed).

Could this be related to the temp gauge not working?
If not, where is the switch that operated the bonnet open light?

Thanks in advance.
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I would have a faults read out from the ECU, it'll tell which connections are at fault. An experienced Alfa mechanic will be able to translate the faults codes to which parts or connection are faulty.
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Quote:
Originally Posted by Nellytheroc View Post
Haven't had a chance to take the temp gauge etc out to check the voltage but I have noticed that the bonnet open light on the dash has stopped working (I rarely run the car with the bonnet open and I always make sure it is well and truly shut after someone told my the catch can be dodgy and the bonnet can fly open at high speed).

Could this be related to the temp gauge not working?
If not, where is the switch that operated the bonnet open light?

Thanks in advance.
The bonnet switch is located inside the left side hole that locates the bonnet securing pin.
It is not necessarily the switch so also check the wiring.

You can have a look in the workshop manual in section 55-8

You can also look in this thread.

http://www.alfaowner.com/Forum/alfa-...-location.html ("Bonnet open" warning switch location?)
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