another thermistor hack

[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.

I tried some of the circuits shown but had some issues with ensuring that I didn't affect the engine temp after the warmup phase. Both the simple resistor and the simple diode setups affected the engine temp after warmup, causing the cooling fans to come on too early and force the engine to always run too cool.

I attached a picture of the enable/dissable switch, the circuit I ended up using, and a picture of the circuit board.

The circuit uses a capacitor to provide a voltage that the car can read.
A set of transistors compares the capacitor voltage to a reference voltage and discharges the capacitor as needed (Purple stuff). Another set of transistors prevents the system from operating until the car is sufficiently warmed up (blue stuff). Lastly another capacitor delays start up, and ensures an orderly "boot" sequence (green stuff).

Effectively the circuit allows the car to warm up to 42C, then suddenly boosts the temp to 73C. The circuit has no effect if the car gets warmer than 73C

I have found this circuit doubles my fuel efficiency.

I should note that I have a Toyota Highlander, not a prius. You would need to atach the leads to the corresponding pinouts for a prius, but it should still work.

As an unanticipated bonus, the circuit also informs you that you have entered "mode three". As you start the car and drive off the temp needle will be pegged low, it will just be comming off of the peg when the circuit swoops it up to just under normal operating temp. As soon as you see the needle in this high temp region you are capable of entering full hybrid mode, but in fact you will be stuck in mode three. So l pull over, stop for ten seconds and voila.

Thanks again for the help, hope someone else finds this circuit usefull.

Legal Note:
I am sure this voids your warranty. There is a risk of damage to the car and or engine. Tinkering with electrical components also can cause fires. Use at own risk.

(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.)

[jstcd]

j

[diamondlarry]

Originally Posted by ken1784

Warning: This modification may damage your cold engine.

Hello all,

Bob Wilson is doing a thermistor hack to reduce warming up fuel on his NHW-11 Prius.
http://hiwaay.net/~bzwilson/prius/pri_temp.html

I would like to report another solution to hack the current NHW-20 Prius thermistor, the THW sensor for engine coolant.
Please refer to attached picture.

Left picture: the original THW engine coolant thermistor sensor connection to the pin E4-19 of engine ECU.
The resistance value of the thermistor is approximately 1085 ohm at 40C, 430 ohm at 70C and 240 ohm at 90C.

Middle picture: a simple solution. You do not need to cut any wire. Just connect a switch, 1k ohm variable resistance and 240 ohm fixed resistance.
When the switch is off, the thermistor works as original, no modification.
When the switch is on, the resistance value to the E4-19 pin becomes combined value with the original thermistor and manual resistance value.
We only can reduce the combined resistance value on this simple solution.

We know Prius coolant temp needs to be above 40C to move to S2.
So, if we could make the combined resistance value to 1085 ohm or smaller, Prius thinks it doesn't need initial warming up and moves to S2 directly.
If we could make the combined resistance value to 430 ohm or smaller, Prius thinks it already finishes warming up and moves to S4 directly.
This simple solution only reduces the combined resistance value. We can't increase combined resistance value, which means we can't fake it is cooler than the real coolant temp.

Right picture: a complex solution. You have to cut the original THW wire.
However, You can fake any coolant temp as you like.
When switch to true position, the thermistor works as original, no modification.
When switch to fake position, you can let the ECU know any temp you like.

Enjoy,
Ken@Japan

Does anyone happen to have a picture of where to locate pin E4-19 of engine ECU? Are the plugs labled under the dash? I would hate to get the wrong one.

[efusco]

Originally Posted by diamondlarry

Does anyone happen to have a picture of where to locate pin E4-19 of engine ECU? Are the plugs labled under the dash? I would hate to get the wrong one.

http://priuschat.com/forums/prius-mo...tml#post694315

[JoesMorgue]

Can somebody explain how doing this to a cold engine can cause damage? As far as I can tell, cold oil will work just as well as normal temp oil...

Originally Posted by ken1784

Warning: This modification may damage your cold engine.

Hello all,

Bob Wilson is doing a thermistor hack to reduce warming up fuel on his NHW-11 Prius.
NHW11 Prius Temperature Hack

I would like to report another solution to hack the current NHW-20 Prius thermistor, the THW sensor for engine coolant.
Please refer to attached picture.

[Dan.]

Originally Posted by JoesMorgue

Can somebody explain how doing this to a cold engine can cause damage? As far as I can tell, cold oil will work just as well as normal temp oil...

I don't think it WILL cause damage, the statement was simply that it MAY cause damage.

Another way of stating it would be:
"All the PhDs at Toyota say not to do this, but if you want to do it anyway.... here's how".

There are 1000's of decisions the Prius makes every second and a large portion of them take temperature into account. By operating outside of the operational parameters of the Toyota PhD's you may come across something that they have never seen before, and as such, never tested for before.

Fantasy below

For all we know the 60+ second S1 warm up phase may be masking some obscure gasket that doesn't react to pressure properly when cold. It may have never shown up under testing because the S1 warm up phase gets the gasket warm before it takes high pressure. With the thermo hack, you can reduce what could have been (in Canada) a 15 minute slow transition from S1->S2->S3 into a 10 second S1->S3.

So basically you will be operating your vehicle in a configuration that may not have been fully tested or planned for. For me... I'd do it in a heartbeat... I think the Prius is much tougher than the Toyota PhD's spec'd it for, but to be fair to Ken, it is kinda necessary to warn people to do this at their own risk.

11011011

[jbumps wvu mntrs]

Originally Posted by ken1784

Warning: This modification may damage your cold engine.

Hello all,

Bob Wilson is doing a thermistor hack to reduce warming up fuel on his NHW-11 Prius.
NHW11 Prius Temperature Hack

I would like to report another solution to hack the current NHW-20 Prius thermistor, the THW sensor for engine coolant.
Please refer to attached picture.

Left picture: the original THW engine coolant thermistor sensor connection to the pin E4-19 of engine ECU.
The resistance value of the thermistor is approximately 1085 ohm at 40C, 430 ohm at 70C and 240 ohm at 90C.

Middle picture: a simple solution. You do not need to cut any wire. Just connect a switch, 1k ohm variable resistance and 240 ohm fixed resistance.
When the switch is off, the thermistor works as original, no modification.
When the switch is on, the resistance value to the E4-19 pin becomes combined value with the original thermistor and manual resistance value.
We only can reduce the combined resistance value on this simple solution.

We know Prius coolant temp needs to be above 40C to move to S2.
So, if we could make the combined resistance value to 1085 ohm or smaller, Prius thinks it doesn't need initial warming up and moves to S2 directly.
If we could make the combined resistance value to 430 ohm or smaller, Prius thinks it already finishes warming up and moves to S4 directly.
This simple solution only reduces the combined resistance value. We can't increase combined resistance value, which means we can't fake it is cooler than the real coolant temp.

Right picture: a complex solution. You have to cut the original THW wire.
However, You can fake any coolant temp as you like.
When switch to true position, the thermistor works as original, no modification.
When switch to fake position, you can let the ECU know any temp you like.

Enjoy,
Ken@Japan

Can anyone that has used this hack, or has more knowledge of EE than I do, provide some more info? If I print out this schematic of the new "complex" version of the hack and take it to Radio shack or similar, would they be likely to know how to interpret this and provide me with everything I need? Also, is this hack the same as the one of the guy on the CNN clip on cleanmpg - he can instantly get feedback from one of his SGII's and turn the temperature up to where ever he wants- same or no? Thanks to anyone who can help!

[Bob64]

I'd imagine the 1k variable resistor to be some sort of dial resistor, where you can turn up or down the resistor value. the 240 is fixed.

I just thought of something... what temp would the car think its running at on the complex diagram when your in the middle of switching to the fake circuit (100% resistance or wire cut)?

[TheForce]

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

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

[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....