The temperature gauge is not always working

[ruben1218 Lurker Find all posts View Profile Close ruben1218]

Hello everyone!

I've recently bought a 2003 Prado with a VVTI 4.0L engine. It's running fine with the exception of the temperature gauge that doesn't work 1/4 of the time. Let me explain this and what I've noticed.

Sometimes, the needle of the temperature gauge stays at the very bottom, as if the car wasn't started. I first thought that this was happening only when starting the car too quickly but it's not the case. Once the temperature gauge works, it won't ever stop working while I'm driving. It either works from the moment I start the car until I shut the engine off or it doesn't. Whether the gauge will work or not seems to be completely random. So far I haven't been able to correlate this with the duration of the previous drive, the way I start the car or anything else I've tried giving a small hit in the dashboard to rule out the needle being physically stuck, which didn't change anything.

I've found some similar issues on internet. Unfortunately, some of the jargon used here was not clear to me so I am trying to have some explanations with simple words.

From my understanding, it's unlikely that the needle would be stuck. Possible causes of this issue would be:
- a faulty wire somewhere
- a faulty coolant temperature sensor (is it the same thing as the temperature sending unit? or are those 2 different things?)
- a dry joint on the electronic board (which would explain the randomness of the issue)

I am now trying to rule out some of the possibilities, but it would be nice to have some more guidance here on what I can test. I have a multimeter. I've been able to locate the sensor, behind the engine, thanks to another post on this forum. However, I couldn't understand how I would possibly reach the cable and disconnect it.

One important thing I have noticed is that sometimes, randomly, right after turning the key (without starting the engine), all the needles are slightly shaking for 2-3 seconds and then stabilise. Not sure if this would have anything to do with that, but it's probably worth mentioning it.

Does anyone have an idea on what's going on here?

Thanks for your help.

[ruben1218 Lurker Find all posts View Profile Close ruben1218]

If anyone ever has a similar issue, you should know that an electrician specialised in cars is probably better at diagnosing this kind of issues than a mechanic. I've brought mine to Automotive Electrical Designs in Fremantle, it cost me 35$ to understand what the issue is and get a quote. I'm really happy with their service, Mark is a real pro.

It seems that it would either be the motor of the needle or a dry joint on the circuit board of the instrument panel. I can let them take it out and send it to a specialist to fix it in 2-3 days for 280$ which seems reasonable, and can even save a bit by taking the instrument panel out myself or even try to fix it.

I've also learned that it was unlikely that the temperature sensor would be defective as it usually completely stops working. Mine fails randomly.

[ruben1218 Lurker Find all posts View Profile Close ruben1218]

Just got an OBD2 scanner today fo 39$ (thanks to this amazing post https://www.pradopoint.com.au/forum/...n-m-obd-prados) and it's actually a pretty easy way to know whether your coolant temperature sensor works or not. It allowed me to confirm that my sensor is working perfectly fine.

I've removed my instrument cluster and while doing that, I forgot to use tape to mark the exact position of the needles of the gauges before taking them off. Recalibrating them is pretty easy though as my OBD scanner is giving me the RPMs, the exact temperature of the engine and using my GPS I can figure out the exact and real speed I'm driving at. Only the fuel gauge is a bit trickier to adjust as you need to be low on fuel and have the warning light on before knowing how to adjust it. The good thing is that I can even adjust them better know, by setting the real speed on my speedo and adjust the fuel gauge to reach "E" exactly when the low fuel warning light would light up. This means that I can go slightly under E before running out of fuel but I find it a more accurate indicator of my fuel level as I should avoid getting in that danger area anyway.

I had a look for a dry joint in the area where the stepper motor for the temperature gauge is located, and everything seemed okay. I found out that the stepper motor I needed to replace was a PPE+PS 6S (the reference is written on it), which you can find for less than 10$ on AliExpress or for 30-40$ on Amazon. Don't get ripped off by paying more than that, it costs literally 2$ to produce this part.

I've decided I will unsolder the previous one and replace it with the new one myself. The 280$ asked is a fair price because they have to take off the instrument cluster, send it to someone else, unsolder the motor, solder a new one, send all back and put it back in the car. Very easy to do but it takes a bit of time and not everyone is able to solder things, but as I am able to do that myself I'll just do it.