Water temp failure

[Troclo]

Hi Guys.

My m84 read error in water temp ( ET ) but after a changed the temp sensor and checked all the wiring I can only conclude that the output AV2 ET is fried, has this happened to anybody else?

Can i just use AV3 instead and is there anyway of measuring if AV2 is faulty? Think I read somewhere that there should be 5v if no sensor connected…

Thanks

[sardengineering]

Good day,

From your post you have described the installation of a thermistor on an analog voltage input, did you type this incorrectly? For engine coolant temperature AT2 should be used, if there's a problem with AT2 then you may also use AT3 as it is a user definable analog temperature input channel. I'm afraid that AV2 is a locked input dedicated to manifold pressure while AV3 is also a locked input dedicated to mass air flow, both AV2 and AV3 don't have internal resistors fitted to support analog temperature circuits.

Analog voltage input channels differ from analog temperature channels so although they may appear to be similar they work differently. Please do take the time to verify the details you have posted and send a follow up response to confirm.

Thanks for choosing the MoTeC brand, cheers!

[Troclo]

Thanks for your reply.

I run (I think) a variable resistance 2 wire temp sensor. It use to work but just suddenly malfunctioned. Changed it with
a new one but still dosnt work. I didn't make the wiring harness myself, but it use to work. Ive bought an untermed
harness now but havnt gotten around to fit it yet.

[sardengineering]

Good day,

You're more than welcome to have online support and assistance where feasible, for the most part this forum has the resources to facilitate such.

What I can advise as a follow up to your response is that using a terminated harness which doesn't have any supporting documentation can be problematic should unfavorable circumstances unfold. Starting from a fresh harness is always going to make your immediate work as well as long term objectives/functionality much easier. Try to keep mindful that the documentation of any harness constructed is of equal importance to the construction of the harness itself.

An easy (basic) way to understand analog signals is that they are divided into two categories, pure voltage signals and temperature signals. AT1 through AT3 are the available inputs for temperature based sensors (thermistors) while AV1 through AV8 are pure voltage signals. You have to remember that most of the analog inputs on the M84 are preset, meaning that the sensor which should be used on each channel has already been predefined. AT3 and AV8 are the only exceptions to this making the parameters user definable, AT3 being temperature oriented and AV8 being pure voltage oriented.

For a little extra insight, you should note that analog temperature inputs have a built in pull up resistor while analog voltage inputs don't have this. In theory you can add an external pull up resistor circuit to the circuit of an AV input to make allowances for the use of a temperature sensor on it, however, this is purely theoretical isn't an advised practice. I only mentioned it to draw contrast between the differences of the AV and AT inputs on the M84.

What you could have done as well with respect to a follow up test would have been to configure AV3 to reflect engine coolant temperature respective of the sensor being used and see if this provides any feedback which can highlight a conclusion. As a last resort you can measure the resistance across the sensor as you expose it to different temperatures. The temperatures you expose the sensor to don't have to be calibrated as you are only checking to see if it is at all responsive, if you are able to provide an environment with calibrated (controlled) temperatures then this data can be plotted to understand (clarify) the operational scope of the sensor as well as the verification of the existing sensor data being used.

My apologies for the long-winded response but I wanted to ensure that I provided as much insight into sensor functionality and circuit operation so that you might have the best chance at success as you continue to work/resolve the complication.

As always, please feel free to follow up at your convenience.

Cheers!

[Troclo]

Hi Damien.

Thank you very much for your explanation. Your support is very much appreciated!

I will try the AV3 test to verify if the temp sensor is faulty and give you an update.

Kind Regards

[sardengineering]

No trouble at all mate!

I'm more than happy to lend my support to ensure that you have the best possible end user experience for your investment with the MoTeC brand.

Take care, cheers!

[Troclo]

Hi Damien, I had a look at the diagram and realized that b16 needs a ground, traced it down the harness, found it plugged on the several other wires.

So unplugged the b16 wire and grounded it, now the water temp sensor works again however the air sensor is now off by some 30 C…(plug it back in and water temp goes off but air temp corrects itself again…)

Wierd thing is that water temp sensor seems to work without b16 grounded swell as long as its not plugged in with the other wires.

Should I keep B16 grounded and rewire air temp (av1) to a new ground?

Cheers

[sardengineering]

Hello and good day,

I can't quite give you a definitive feedback unless you complete a follow up test for me. Would it be possible to wire you own shared ground by passing the ground circuit wiring of the harness? You see B16 is a sensor ground pin and it is quite normal for this to be shared amongst analog sensors. However, it may appear as though something might be wrong. If you were able to hard wire your own ground circuit outside the existing harness and test for sensor verification then I believe you may have an absolute confirmation.

As far as what might have caused things to run a muck, that's something I can't respond to without high speculation. You should be able to go through the harness and pin point the exact fault assuming the advised test validates my suspicion. What I can tell you is that analog circuits and the analog signals thereof are very particular with respect to the ground used.

Question, when you say you unplugged B16 and grounded, can you explain where exactly the new ground was placed? Lastly, you keep noting reference to AV (analog voltage) pins and not AT (analog temperature) pins. Is this deliberate or are you confusing both using them interchangeably by accident? Please note that the M84 has designated pins for each analog voltage and analog temperature inputs, you are not allowed to deviate with the exception of AV3 and AV8 which are user defined in stature.

I really hope that I am helping to aid your progress and not amplifying your complications. At times I find it necessary to adopt an explanatory approach to that an advisory can be comprehensively understood. Unfortunately, this isn't always the ideal to ensure the assistance given has a constructive outcome.

I hope you are much more productive and that I may have helped you expand your understanding, cheers!

[SprinterTRD]

With a multimeter, Check that pins B15 & B16 on the ECU is connected to A10 & A11 ECU Ground.

If it is not connected then at some point +12V has been placed onto the 0V wires in the loom.

Return your ECU to a MoTeC dealer for repair if the connections are not there, and check your loom for faults.

[Troclo]

Sorry Damien, should have said AT1 ( air temp ) I'm not confused though I appreciate it may sound like it!

I grounded B16 to the firewall. Will try the test and will also check if B15/16 are connected to A10/A11.

Thanks again for your quick response and sound advice, great to see that Motec support is so solid!