another thermistor hack

[hill]

Originally Posted by jstcd

Howdy,
Thanks guys for all the info, this thread was a great help in my own attempts to fix the whole warm up issue.

I ended up making a circuit of my own, based in no small part on what you guys did.

. . . . . snip

(so far I have seen no ill effects on my engine, perhaps because I have set the min required warmup to 42, (just past mode1) certainly the car will behave badly if it really is at -5 and you tell the computer it is at 73.)

Can this hack be mod'ed to go immediately to S4 ??

If not, then why?

[TheForce]

Originally Posted by max9952001

Any recomendations for someone who doesn't know anything about circuit boards? I have a hymotioned prius, less than a 5 mile commute and would like to operate all electric. I would be interested in purchasing one of these hacked boards from someone with some detailed information about what it is doing and that the same board has been used on an existing prius....

My auto temp hack project has stalled at the moment. Moving into a new house and I have a trip to Hybridfest in July coming up shortly. After things start to settle down I will try to get the ball rolling again. In the mean time I'm still just using the basic POT resistor combo.

You might want to install a manual EV button since you have a short commute. You can go into EV at startup bypassing the warm up stage. If you do that you still may want to let the car go through S1 every other day or two just to keep things lubed up.

[TheForce]

Originally Posted by hill

Can this hack be mod'ed to go immediately to S4 ??

If not, then why?

No immediately. For best relults the actual engine temp must be 100F+ before you crank it up to 159F. If you dont let the engine get to 100F it will start to stutter if you fake the temp. You can however get into S4 after you go through S1. You could get into S4 in as little as about 2 minutes. Thats just my guess. I never have the opertunity to try it out on my commute. Plus I have no need for S4 on my commute with the temp hack. I think I mostly stay in S3.

[max9952001]

I do have the EV mod from coastal tech, but it will display "can't change to EV mode now" at startup - seems I have to get to 125 F before it will engage. So my engine runs for about 2 minutes and then I'm electric. I'm still getting great mileage, just was wondering if I could bypass the gas engine with the short trips when there is plenty of hymotion battery.

Originally Posted by TheForce

My auto temp hack project has stalled at the moment. Moving into a new house and I have a trip to Hybridfest in July coming up shortly. After things start to settle down I will try to get the ball rolling again. In the mean time I'm still just using the basic POT resistor combo.

You might want to install a manual EV button since you have a short commute. You can go into EV at startup bypassing the warm up stage. If you do that you still may want to let the car go through S1 every other day or two just to keep things lubed up.

[jstcd]

Ok, so its over a year now that I have been driving with the hack and: No obvious damage so far to my engine, and way better mileage. I have forgotten it it's a hack, and think of it as part of how the car behaves. I love it but obviously I’m biased.
Answers to questions:

1) Why can’t you just jump right to S4?
The system tricks the computer’s temperature sensor. BUT Temperature is used for things other than the hybrid warmup cycle. Specifically engine timing and air fuel mix. If you fool the car into thinking it is warm when it is in fact too cold, the engine will run progressively rougher and eventually stall. I imagine you would eventually also damage the engine. Also, if you spoof too early the computer will notice, it will throw an engine error light and it will flag your temp gauge as broken. You will need a scan tool to reset the light and tell the engine the temp gauge is fixed.
That said, by adjusting the "start spoofing" potentiometer, you CAN do it, I tried it, but only once.


2) What transistors? They are just standard general purpose silicon transistors, almost anything would do, but two are NPN, and two are PNP, you must get that part right. The actual ones I used were: NPN: 2N4124 and PNP: 2N3906.

3) What is the not gate?
Note that the thick dots on the diagram are just connection points. At the point pointed to by the "not gate" arrow, the voltage will be high when the temperature THW pin is low, and the voltage will be low when the THW temperature pin is high. Thus at that point the voltage is the inverse (or "NOT" function) of the car’s temperature signal.

4) Will it work on a prius?
Obviously it works on a highlander, I have read the prius factory repair manual, and the temp sensor circuitry is pretty much exactly the same as far as I could see. In fact this circuit should work in probably any car. The only difference is the pinouts for a prius and a highlander are different. You must connect your circuit to the right points.


Notes:
If you do try to build this, do it on a breadboard, and play with it, understand it, make sure it’s working, before installing it in your car. Use a resistor to simulate "CAR" and a potentiometer to simulate the engine temp sensor.
I know it’s a complexish circuit, but it really isn’t that hard to build. The majority of the complexity is due to my wish to not have the real car temp signal compromised anywhere but in the region I wanted it to be spoofed. I tried a lot of simpler circuits, and found my cooling system trying to max itself out before my car was even at temp. Unwanted voltages created by simpler circuits can have unwanted effects on your car as the temperature sensor of the car is very sensitive.

Not shown in the diagram, but in the picture, I used a single pull double throw switch so that both the points at which the circuit connects to the car can be disconnected at the push of a button.

[donee]

Hi j..,

Is your circuit posted somewhere? My take on this is it really needs to be a microcontroller which reads actual engine coolant and oil temps, and then spoofs the car. And it would have selections for like PHEV , Charge Sustaining and Short Trip modes of operation.

[jstcd]

The circuit is in the "attached thumnails" of my original post, back on page 2.

I had thought of doing this the microcontroller way, but this seemed simpler. Had this not worked, I was going to do just that. Ultimately, even the microcontroller is going to turn on and off a reference voltage, all I did was use some transistors to do the switching, since the overall logic is so simple:

Engine below T1--> no spoofing.
Engine above T1 but below T2 --> Spoof T2.
Engine above T2 --> no spoofing.

All the circuit really is, is two reference voltages, and transistors that switch on or off depending on the engine's temp relative to T1 and T2 thus enabling or disabling the simple spoof circuit.

However with a microcontroller, and maybe a bit more info from Toyota, you could do some pretty cool spoofing.
One major improvement that might be possible: Maybe you could only spoof when the ICE was OFF, or the throtle being released. IE turn the spoofing off when the engine is supposed to be running, and only use it to keep the engine off during coasts and stops. Thus the fuel mix and timing would not be affected by the spoofing.

Even better, a microcontroller might be able to just send the appropriate CAN message to the car's computer that warm up was complete.

What I'd really LOVE to do, is fool around with the ECU code and tweek it so that the car does what I want it to do withough having to fool it, but without Toyota giving me accsess to the code, and documentation, (not a chance) I this will remain a pipe dream.

Originally Posted by donee

Hi j..,

Is your circuit posted somewhere? My take on this is it really needs to be a microcontroller which reads actual engine coolant and oil temps, and then spoofs the car. And it would have selections for like PHEV , Charge Sustaining and Short Trip modes of operation.

[TheForce]

I'm wanting to build your design but I'm not sure on what some of the stuff is in your schematic.

Can you tell me what the transistor values are? And can you tell me what the "NOT" gate is? Is it just a connection or is there an actual NOT gate there?

[Dan.]

Originally Posted by TheForce

I'm wanting to build your design but I'm not sure on what some of the stuff is in your schematic.

Can you tell me what the transistor values are? And can you tell me what the "NOT" gate is? Is it just a connection or is there an actual NOT gate there?

OK... think I'm about ready to do the hack. Had a few "Ohms Law" type questions.

If the Prius uses a

thermistor

Thermistor

, why is the data I'm reading correlating certain temperatures to certain voltages, instead of correlating temperature to a certain resistance, as I would think most thermistors would? With that said, does anyone know the resistance across the thermistor at 40°C verses the resistance across the thermistor at 70°C and 90°C. Also does the thermistor's resistance raise with an increase in temperature, or lower? Since this hack has the resistors in parallel, I would think the resistance must drop as temperature increases.

I know others have suggested a 240Ω resistor with a 1K POT in series with a switch, but aren't there some POTs with a built in switch, turn it all the way counter clockwise and a bit further to click it off? Would a really big logarithmic POT (1M) with a built in switch work? Turn it on and it's at 1MΩ with almost no effect on the original circuit, then as you dial down the resistance on the POT, the effect becomes more substantial.

Anyway... Thanks to everyone for coming up with this hack!

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[Dan.]

Originally Posted by Dan.

OK... think I'm about ready to do the hack. Had a few "Ohms Law" type questions.

If the Prius uses a thermistor, why is the data I'm reading correlating certain temperatures to certain voltages, instead of correlating temperature to a certain resistance, as I would think most thermistors would? With that said, does anyone know the resistance across the thermistor at 40°C verses the resistance across the thermistor at 70°C and 90°C. Also does the thermistor's resistance raise with an increase in temperature, or lower? Since this hack has the resistors in parallel, I would think the resistance must drop as temperature increases.

I know others have suggested a 240Ω resistor with a 1K POT in series with a switch, but aren't there some POTs with a built in switch, turn it all the way counter clockwise and a bit further to click it off? Would a really big logarithmic POT (1M) with a built in switch work? Turn it on and it's at 1MΩ with almost no effect on the original circuit, then as you dial down the resistance on the POT, the effect becomes more substantial.

Anyway... Thanks to everyone for coming up with this hack!

OK, sleep cleared it all in my head. I looked at Bob's page again and saw the other resistors behind PIN 19
So effectively what you have (sorry no art skills here) is:

5V-----R1-----a------R2------b------GND

R1 = Internal resistor
R2 = Thermistor
a = Sample Point
b = Sample Point

Now the ΔV between "a" and "b" is I*R2, and 5V=I*R1 + I*R2, so I = 5V / (R1 + R2)

so the ΔV between "a" and "b" is 5V * [R2 / (R1 + R2)] or

5V * α where α = [R2 / (R1 + R2)]. This makes since since as R2 approaches ∞, α approaches 1, and as R2 approaches 0, α approaches 0.

Anyway, I got the range of the Thermistor (R2) from Hobbit's graphic as between 79Ω (@+140°C) and 156KΩ (@-40°C), but I don't know what it's "operational" range is at temps between 40C and 95C. I also have no clue what value R1 is either.

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