There’s plenty of threads about this but none with the answer I’m looking for.

Also, this isn’t for a Ford truck (gasp!) but I’ve asked around on several forums (as well as googling it) and it seems what I’m looking for either doesn’t exist or very few people have tried it. I’m guessing the former but we’ll see.

Does anyone know of a trans fluid temp gauge that can be spliced into the factory wiring and read accurately? I need to know trans fluid temp on my wife’s van to get an accurate level reading, but I’m just not interested in adding a separate temp sensor to do it. IMO it’s just creating a future leak point.

I read on a couple of forums where they installed the sensor by splicing into the factory wiring and said “it’s working fine” but they don’t say anything at all about verifying it’s accuracy by comparing to live data.

This is strictly a convenience issue so I’m willing to try a few different things but I’m not gonna invest a lot of time in it either. The point is to have a relatively quick install.

Thanks.

 

Given this, I don't think so. That said, there are many other inmates that have more automotive knowledge than I. Someone else may have a more thorough answer (and more to your liking).

On an old Explorer, I installed a remote trans. filter and added a mechanical temp. sensor to the filter base. It worked great but it wasn't 'relatively quick' nor was it making use of the existing wiring harness. Another downside, to my install, was that I wasn't really measuring fluid temp inside the transmission (where it's most critical). I never had any issues with leaks (but, I understand your point).

I hope there's a quick/easy way for you to get what you're after but my guess is there isn't.

 

I meant relatively quick in comparison to having to install a sending unit just for the gauge - I know it’s not gonna be a fast job.

My plan B was to install a gauge as I want it and then compare its readings to live data on a scan tool - if it’s only off by a few degrees I can live with that. I’ve just been trying to find a gauge that was either capable of reading the factory voltage or could be calibrated to do so.

 

Not sure if the signal is going to be volts or amps. If the signal is volts (not atypical in my industry at least) you'd need a decently high impedance circuit to read the value w/o affecting the car's computer. If it's already converted the signal to amps there's virtually no issue with borrowing the signal for something else.

If you can pull the data out of the OBDII connector that would be quick and "easy" (SMAP?).
I've been wanting to get one of those in-situ OBDII readers for a similar purpose.

 

The problem with doing this is that splicing into the factory wiring is going to change the data that the van's computer is going to see. So you won't create an additional leak point, but you potentially will screw up the computer or the transmission by changing the temperature reading. And you won't get an accurate reading on any gauge that you install using this method. I strongly advise against this.

There are several choices of free or very inexpensive (<$30) ways to read data from the computer for Ford vehicles. I expect there are similar programs available for other makes, too. These plug into the OBD port and you can read transmission temperature (and many other parameters) very accurately.

 

Can you please elaborate Mark on how we can read the data from the computer? I know more modern vehicles do this but I didn't know we could do it through the OBD port.

 

I've used a Bosch 1300CA scan tool that you can get live data from using an OBD 1 adapter cable. Same one that auto parts store rent out.

 

If your EEC-4 is new enough to output DLC through the OBD-1 diagnostic port, and there is a trans temp sensor there, you can read trans (oil) temps. This would be the same sensor the ECU uses to know when converter lock-up schedules can be utilized for electronic automatic transmissions.

I used EASE Diagnostics back years ago, to view, plot and datalog engine and transmission info for tuning for EEC-4/OBD-1 vehicles, and there may be others out now that can do something similar.

 

Ok, this is already getting much more discussion than I’ve seen on other boards, so let’s dig in. The other boards I’ve posted on about this got a “Hey that’s a neat idea response” but not much in the way of stimulating conversation/providing facts.

I’ll preface with a little more info:

1) I’m an auto tech by trade (3 yrs experience at this point), so while I do have knowledge of general automotive principles, I’m not particularly familiar with any one make or model nor am I familiar with a lot of aftermarket products (the customers we have that want aftermarket mods are few and far between so I’ve had little need or desire to learn more about them). That said, I consider the only dumb questions to be the ones you don’t ask - that doesn’t mean, however, that you can’t make fun of me for asking them.

2) In case anybody can find more info about it than I can (I have access to Identifix and Pro Demand), I’m wanting to install this on my wife’s van- 2016 Grand Caravan RT with a 62te trans. The only info I’ve found on the TFT sensor is it’s part of the valve body/solenoid assembly - no info on its operation. I’d like to ASSume it’s a standard negative coefficient type sensor but I haven’t been able to verify that and it’s integrated into the assembly so it can’t be replaced on its own.

3) If I wanted to purchase a small scan tool or OBD adapter for my phone to read live data, I would. But, I don’t want to, which is the reason for asking people who know more than me if this is a viable option. The point of wanting this gauge is for the convenience of it - so I don’t have to screw around with a scan tool or my phone for one small piece of data that should have been easily available on the DIC to begin with, DODGE!!!

When I have used the scan tool in the past to check the TFT, live data reads a temp and a voltage signal. I haven’t yet had the opportunity to analyze the voltage to temp relationship to determine what I should be seeing as the temp changes.

How do you figure it will screw up the signal to the computer? I’d be splicing it in as a parallel circuit, so in effect it wouldn’t be any different than using my meter to probe the signal wire if I were troubleshooting the circuit.

 

If you can get the data, it's probably easy enough to map it. Not sure how the signal is generated but in many cases, over a small enough range temp to volt conversion is fairly linear.

It could be very different than probing with a meter.

A good DMM is very specifically designed to have a high impedance on the volt measurement. What that means is that the DMM doesn't affect the voltage much when you probe a signal. However, I would be highly doubtful that a cheap (remember that cheap is relative. a good DMM is ~$200) gauge would have the same sort of design.
Also, why would they design the gauge to have high impedance? It's meant to attach to a sending unit. To ease installation, it would make sense to power the meter from the sender if possible. Or just to save money, I wouldn't waste time and components on making a high impedance gauge.

Some temperature converters use very small (tens of microvolts per degree) signals to send voltage signals. Again, I'm not sure what they're using in the transmission but there aren't too many options if the signal is voltage.

 

I have a free program called Forscan. It only works on Ford vehicles. There may other programs that work on other makes, I don't know. To connect my laptop to the vehicle I had to purchase an ELM device that was less than $25 at Amazon. The ELM should be universal, but Forscan won't talk to other makes.

The data is there and available, all you need is the right tool to access it.

 

I need to do the same on one of my Mopars, but I won't be taking your approach with regard to finding a way to read the trans temp via OBD.

I have an ISSPro Trans Temp gauge that I used in the E4OD of my F350 before I did my ZF5 swap, so my plan is to use the temp probe and a clipsense attachement and simply attach the sensor externally to the cooling line coming FROM the transmission to get the hottest flowing fluid temps. There will be no leaks, wiring up the sensor and gauge is easy, and the gauge can be stashed out of the way for me to read as I drive. I expect the reading even with the clipsense attachment to be within 5°F of what it actually is for the sake of accuracy.

This way I don't have to fiddle with an OBD reader, bluetooth to the phone or laptop, and software.

 

why are you needing that close of temp reading on a van? is it giving you that many issues? is it because it doesnt have a dip stick like so many of these new vehicles have gone to, seems like your company could have access to your wiring harness diagram and you could trace your wiring to see if/what voltage it read, We use red line gauges that are 0-5v, 0-10v or 4-20mA, by setting dip switches.

 

Most temp sensors you see on today's vehicles (such as a coolant sensor and I'm guessing the sensors that are provided with most gauge kits) are negative coefficient type sensors - as temp goes up, resistance goes down, and the voltage signal increases.

I suspect the TFT sensor in the trans is of the same type, but I simply haven't had time to monitor the signal long enough to determine if that's the case or not. It's my wife's DD and our weekend vehicle, so the time I have to service it (whether it's an oil change or repair) has to be planned in such a way as to not interfere with that. Could we get by without it if we had to? Yes, but I'm not going to let the reason we have to do without it be because I was busy tinkering with it.

Trying to determine how different gauges work is the other bit of info I haven't been able to find. I'll be the first to admit I'm not that good with google, or yahoo, or any other search engine, but the best I've been able to find is gauges for sale on amazon, ebay, etc. and the product details on those pages just don't provide the information I need to determine what type/brand of gauge will work best if I'm going to attempt this.

I get what you're saying about the meter being high impedance (mine is a Fluke 87) but in a parallel circuit, voltage is the same across every branch of the circuit, regardless of what the total circuit resistance is. Even though the meter is high impedance, it still has to have a ground before it reads anything - that means voltage must drop across that resistance (making it the load) to complete the circuit, even it's only a very small amount.

It doesn't have a dipstick from the factory, but I have the "special tool" that Dodge requires to check it. It's just a dipstick with depth readings marked every 10 mm, but their method for checking it relies on knowing the fluid temp. You compare the fluid temp to a chart and it gives you a range of appropriate depth for that temp (for example, it should be between 8-25 mm at 100*F) For anybody (Dodge tech or otherwise) to accurately check the fluid level, the scan tool has to come out for the fluid temp reading.

No, the van isn't giving us any issues at all. Which is exactly why I want to keep it that way by accurately checking the fluid level on a regular basis.

The other issue I have with installing a separate sensor for a gauge is where it should be installed for the most accurate reading. I read plenty of posts where it was teed into the cooler line, or installed in the test port, or a hole drilled in the pan... and every single one of them was off compared to live data. Maybe it's a location issue and maybe it's a cheap sensor issue - I don't know, but it's another reason why I'm attempting to figure this out.

This isn't a must have for me - I will get the scan tool or OBD adapter if it has to be that way - I just don't think I have enough information at this point to determine it's just not possible.

I believe this is possible, it's just an issue of how. Like the little engine that could, "I think I can...." - as if optimism could overcome a poor horsepower to payload ratio, gravity, and other basic laws of physics!

 

I can’t help you with your dodge van but if you had a ford I’m already doing exactly what you want to do but with more sensors. If you tap into an existing sensor and don’t load it down it won’t effect the sensors reading, I’m doing this by running it into the Analog to digital converter of an Arduino.