Gauge Problems... Total Frustration
 

Hi all. I haven't posted too often in these forums, but I want you to know that I've done extensive research on all of the following problems. My fuel gauge reads incorrectly, my coolant temperature gauge stays at the bottom, and so does my oil temperature gauge.

FYI I drive a 2001 A4 1.8T Quattro.

As for the fuel gauge issue, I am aware of the standard fix with the fuel level sending unit. I've cleaned mine numerous times, it almost sparkles now. I've also tried swapping in another one from a used A4, but get the same problem. When my tank is full, the gauge reads a little over 3/4. After 120-150Kms the gauge reads empty. Normally I get ~450Kms per tank, so thank goodness my odometer and trip-meter work fine. It should be noted that the gauge doesn't suddenly drop or increase, it slowly falls down to the empty mark (albeit much faster than it should).

I have put in a brand new coolant temperature sensor in behind the engine, and that didn't change my gauge issues. I've read that sometimes a faulty thermostat can cause the gauge to not work correctly, so I put in a new thermostat today. Still no change.

Now for the oil temperature gauge, I'll be honest: I haven't done any research on this. I've been too busy trying to fix the fuel and coolant temp gauges. My oil temp gauge moves slightly once the engine is warmed up, but barely. Perhaps this isn't a problem, but I'm listing it here anyways.

After all the time and money I've spent trying to fix some of these problems, I'm beginning to think that perhaps they aren't individual issues. Perhaps there is one piece that's screwing with all three gauges.

I thought maybe it was my instrument cluster, so I found a website that tells how to use Vag-com to make sure the instrument cluster is OK (VWVortex.com - DIY - Adjusting the displayed fuel gauge level with a VAG-COM). After performing these steps, I found no problems with the instrument cluster. All the gauges moved the way they were supposed to, and didn't get any error messages.

I did scan the fault codes in the instruments panel and found
00771 - Fuel Level Sensor (G)
30-10 - Open or Short to Plus - Intermittent
And Unfortunately I didn't save the code I got for my coolant temp sensor. I cleared it before I did the instrument tests, and after driving it a little bit (5 minutes or so) the codes never came back, excluding the 00771.

I'm going to try to post a picture I took of my instrument cluster. I had just come home from filling my gas tank when I took this picture, so you can see that even though the tank is full, and the engine is warm, the gauges are not reading correctly.
Attachment 17142

Anyway, I hope there's someone here who can shed some light on these issues. I'd really like to iron these out, and I've got the time for it right now. Hopefully it won't cost me an arm and a leg.

The items you describe seem to be a wiring issue that may be caused by a faulty earth connection either on the engine or bodywork.

A very minor point, but is your instrument cluster displaying the date correctly as 16 December, or am I misreading it? You must be somewhere in very far east for that to be the case given the current time!!

I am sorry, I was looking at the wrong month of the calendar...today is 16 December...

What do you mean by earth connection? Do you mean grounding? If so, where should I begin looking?

I live in Canada, and it is most definitely December 16th today!

Thanks for the speedy response.

Yes, check to see if the brown wires connected at various points around the engine and bodywork are secure and free of corrosion.

Sorry, English is not my first language, so I think in USA they are referred to as 'grounds', whatever that means, I do not know...

Ok, good news and bad news. The good news is, after driving it for nearly an hour tonight the oil and coolant temp gauges started working! So apparently the thermostat swap did fix those two problems. I also noticed that my car was running smoother, the heater was working better, and the 'miles to go' number increased from 520kms to 610 at one point! Looks like that will help my fuel economy as well.

Bad news: my fuel gauge still isn't working properly. You can see it's still not near the full mark, even though I only drove about 25kms.

Attachment 17143

So! The next question is, whats the next step in figuring out why I don't get an accurate fuel reading?

During your diagnosis testing, did you inspect the wiring to the fuel pump/fuel gauge at the connectors near the fuel tank? If you live where corrosive salt is used for melting the snow, it is possible the connections are corroded.

From what I have seen with the B5 fuel gauge issues, replacing the sending assembly with a new unit having the correct resistance for the gauge to give accurate reading seems to be the best repair.

I have looked at the wiring at the fuel tank, and everything looks fine. It doesn't look like there is any corrosion, and all the connections look clean. I did buy a cheap multimeter to check the resistances on the sending unit, and found that when I used the OHM RX10 setting, I would read 40 at empty and 175 at full. Although I don't know if I was reading the right numbers... I'll admit that this was my first time using a multimeter to do anything but check if batteries were still good.
I should note that both of my sending units gave the exact same values for resistance, which I think would be odd if both were faulty. (I would think that they would give different readings)
Is there a way I can use the multimeter to check the wiring by the fuel tank too?

I'm posting a picture of my multimeter just to make sure I'm using it correctly. I read the 2nd row of numbers from the top (the black text).
Attachment 17144

The correct scale for ohm resistance is the top that is green.

If you have the Bentley workshop manual, it will provide the resistance ranges for the fuel sending unit so you can compare with your readings.

Ok. So then I would have been reading, with the RX10 setting, approximately 18 on empty and 2 on full. Either my multimeter sucks, or else both of those sensors are messed. Might just be time to go to Audi and buy a new sensor, unless there's a place that will sell them cheaper. Last time I called for a price check I think they quoted me between 100-120. I think my local part store wanted closer to $200. Is there any online stores that sell for super cheap?

edit: I don't have a workshop manual. TBH I have no idea where to get one.