Pinouts, please

Could we talk you into getting a Prius-aware scanner like a Scanguage or the Android one?

The Scangauge, XGAUGE function gives you access to up 30 Prius specific metrics displaying four values at a time. You'll have actual engineering metrics and XGAUGE definitions can be changed out for others.

If you still want to use a LED solution, engine running is easy enough but closed loop is a little more challenging. I suppose a linear amplifier trimmed to swing the O{2} sensor voltage to LED range might work.

Just a thought, have you considered picking up the schematics book, used on Ebay? You might also consider Volume 1, diagnostics and Volume 2 repair. These make an excellent library for current and future projects.

Bob Wilson

 

Engine running can probably be LED monitored by tapping any of the following engine ECU signals:

• injector pulse - use pull-up resistor as the signal goes low, pp DI-68.
• igniter pulse - pp DI-120

The engine ECU is located to the right of the glove box so finding and tapping one of these signals should be fairly easy and with a current limiting resistor, work without impacting performance. Volume 1 has a lot of details about the signals and where to tap. The schematic manual includes the color codes and is a little easier to read.

The engine ECU handles closed loop operation by adjusting the fuel trim based upon the O{2} sensor value changes. But these are small voltages, 0.40-0.55 range, and loading the shielded circuits is neither trivial nor wise as we don't know how much current they flow. Worse, the voltage swing is not in normal LED lighting range.

So I would build a small circuit board with a linear regulator, linear amplifier, and trimmer pot to adjust the output range for the LED. The linear regulator provides a constant voltage source for the linear amplifier. The linear amplifier provides high-Z to minimize loading the signal. The trimmer pot adjusts the output to make the LED light work. Then comes the fun part, tapping the shielded, O{2} sensor wire so you can see the signal swings showing the fuel trim is working.

Bob Wilson

 

There are multiple circuits that can monitor the O{2} sensor voltage but it is important they do not inject a load that would reduce the O{2} range or noise.

Another option would be a Zener to provides both power and a known reference voltage. Then feed the O{2} signal into a comparator which in turn drives the LED. One IC, Zener, some current limiting resistors, and a trim pot used as voltage divider and the problem is solved.

The biggest problem with an ON/OFF engine sensor is it does not give the engine RPM. There engine RPM ranges that are desirable and others to be avoided:

• <1,000 rpm - key to entering hybrid mode (i.e., Stage 4) where the engine will shutoff at any speed. Before entering this mode, even at speeds up to 32 mph, the engine will continue to run even if not needed.
• <2,400 rpm - very fuel efficient range supports reasonable acceleration and 90% of urban traffic demands.
• 2,400->3,900 rpm - increasing fuel consumption per unit of power, tolerable but avoid if possible.
• >3,900 rpm - the engine begins using fuel enrichment to reduce exhaust gas temperature and avoid burning out the catalytic converter.

Bob Wilson

 

Seems to me I remember that way-back-when (2002) the guy at CoastelTech sold an LED setup that mounted on the dashboard somewhere. I don't remember what the lights showed, maybe regenerative braking, maybe engine to 0 RPM. Probably not what the OP is looking for but might offer some ideas.
Ed

 

I found it. Brake/Eng Run Kit

 

So, I have a ScanGauge II that's plugged in all the time and sits on top of my steering column. It can show four things at a time. Right now, the four I have selected are aux battery voltage, traction battery state of charge, loop open/closed, and long-term fuel trim. Change one of those to RPM or engine load and you've kind of got what you want, right?

Seems to me the easiest way to find out if the ECM is in closed-loop control mode is to ask it, using OBD-II, and it'll tell you. Otherwise you'd have to be snooping several of its inputs and outputs and analyzing them to see whether it seems to be varying the outputs the way you expect in response to the inputs. That sounds like more of a project than plugging in a ScanGauge to get the answer and display it.

It turns out the answer doesn't seem to be all that exciting ... it's in closed loop within seconds of every warm start, maybe more like a dozen seconds of a first cold one....

-Chap