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Old 11-26-2009, 12:50 PM   #1 (permalink)
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Graham mini scanner - Quick User's Guide


This longish posting is about 'tool usage' of a Graham Davies mini scanner. It covers basic operation to check out the health and status of an NHW11 Prius. This tool only works with the Toyota NHW11, 2001-03 Prius so I've posted it in the "Hybrids" area but I'm not 'hard on' where it goes.


Graham Davies is one of the Prius pioneers who along with the 54,000 owners of NHW11 Prius made a stellar constribution of his Mini-Scanner. He made about 200 of these marvelous instruments until the NHW20, using a different CAN protocol, made them unusable for the next generation. But there are close to 50,000 NHW11s still out there who could use a Graham scanner to diagnose and help correct problems ... to keep these NHW11s running. I now have a second one and am doing 'tool rental' so folks who need to repair their NHW11s can gain more years of service.


The mini scanner has four buttons, a display capable of showing two lines of two data elements, and is powered from the CAN bus where it gets the signals. There are seven lines or rows so a total of 14 variables and be viewed, four at a time. But it is a little tricky to operate so I will make frequent references to this sketch:


The left-most, standalone button is reset. When the ignition is on, the mini scanner remains inert until the reset button is pressed. The scanner remains on until the car is turned off. Hitting the reset is the same as the initial power on state and after initialization, puts the mini scanner in "Display 7" mode.

Line 7 - showing MG1 C and MG2 C
Line 1 - showing ICE C and ICE rpm

MG1 and MG2 temperatures are a primary indication of their health and status. When the Prius is warmed up and operating at speeds under ~65 mph, the normal temperature relationships including engine should be:

* 85C - ICE coolant temperature
* MG1 C < ICE C - MG1 has to carry about 28% of the ICE power in or out so in addition to be closest to the engine block, it tend to run warmest of the two MGs but cooler than the ICE.
* MG2 C < MG1 C - at ordinary speeds up to about 65-70 mph, a healthy MG2 will be cooler than MG1. But if MG2 is running warmer than MG1, we begin to worry about shorting or a cooling problem. This is a bad thing that is associated with transaxle failure.
* MG1 C and MG2 C > 100C - heat is the enemy and running at speeds that heat MG1 and MG2 above boiling is going to shorten the transaxle life. In fact, I prefer to to treat 90C as the warning level and at 95C, I slow down NOW! Speeds in excess of 75 mph on hot days and in mountains can easily bring the MG temperatures above 90C range. In such conditions, I recommend keeping your climbing speeds to 55 mph since this is both engine and vehicle efficient and 55 mph up a mountain is much nicer than the alternative.

There are three buttons on the right, a center "mode" button, and two option buttons. By pressing the "mode" button for about 1 second, the "Favorite Select" mode occurs and all data lines can be displayed. Use the "right" button to go up and the "left" button to go down. It does not "wrap."

Line 2 - Traction Battery Min V and position
Line 3 - Max Battery C and Max V

The NHW11 traction battery has 38 modules grouped into 19 pairs numbered 1-19 from the control electronics. Each module has six cells at ~1.2 VDC or 7.2 VDC for the nominal module volage. Two modules together give a voltage of 14.4 VDC. But in practice, the per cell voltages can go a little higher, up to 1.4 VDC in part due to charging needing extra voltage to push current into the cells.

We are looking for a low module-pair that is 1.2 VDC or lower than the maximum module-pair. This is the signature of a failed cell inside a module. A failed cell can not be repaired so the module has to be replaced and/or the traction battery pack refurbished. Regardless, that traction battery assembly has to come out.

The other problem is a failed or failing module will start running hot. Heat is the enemy! Since the electrolyte is a saturated KOH solution, if the temperatures approach 100C, the internal cell pressures will become very high and this can lead to other 'bad things:'

This is an NHW20/ZVW30 battery pack that was over charged.

Line 4 O1 V and O2 V sensors

The NHW11 uses a fuel trimming algorthm that requires two oxygen sensors. As the engine runs, it cycles between a slightly rich and lean mixture causing #1 oxygen sensor to swing ~100-800 mv. The exhaust gas then passes through the three-way catalytic converter where #2 sensor sees a smaller swing. The catalytic converter has combined the NO{x}, CO, and hydrocarbons into mostly nitrogen, CO{2} and water vapor. Both sensors need to work and #1 must have a larger swing than #2.

The NHW11 also has a hydrocarbon capture system just before the catalytic converter that has mechanical linkages. These can corrode and should be inspected, tested for smooth operation and lubricated with a high-temperature grease if living in salty areas.

Line 5 AccM V and AccS V

The NHW11 uses a mechanical, dual potentiometer encoder on the accelerator pedal that are resistance offset but otherwise linear. Some of them develope 'noisy' wipers and this can confuse the hybrid vehicle ECU. Not knowing which is right, it goes into a "safe mode" also called the "big hand" syndrome. By slowly pressing the accelerator, and monitoring the voltages, look for swings or jerks, the symptom of noisy contacts.

Doug Shaffer pioneered how to disassemble, clean and reassemble the encoder or you can get a new one from Toyota for about $500. I also clean them on an exhange basis:

Line 6 MG1 Nm and MG1 rpm

MG1 along with the Power Split Device are the "variable" part of the CVT transaxle. Due to gearing, MG1 Nm torque is 28% of the engine torque. If you divide the MG1 Nm by 0.28 and multiply it times the ICE rpm, you have the engine shaft power to the transaxle. It is a built-in engine dynanometer.

MG1 also has two modes: generator and "energy recirculate" (also called heretical.) In generate mode, MG1 provides counter torque to the engine and everything combines in MG2 to drive the car. But in "energy recirculate" mode, MG2 generates power and MG1 works like a motor to slow the ICE rpm ... a kind of 'over drive' and very efficient at high speeds.

Line 7 MG1 C and MG2 C

Our old friends, the temperatures of MG1 and MG2 that should be kept under 100C by conservative (and fuel saving!) driving.

LINE 1 select
LINE 2 select

By pressing the middle button for a second, the cursor moves to a new line and blinks. Using the left and right buttons, one can select a new data item to display. This is part of how the Graham scanner is programmed:

Options 2

Pressing the middle, mode button allows changing the number of lines reports out the RS-232 serial interface and the poling rate. I have it programmed for six lines and the fastest poling rate, just over 1 second for all six lines.

Trouble code

Pressing the middle, mode button allows use of the right and left buttons to display the recorded engine, hybrid and battery error codes. Then holding the right button for ~3-5 seconds, it lets you reset these codes.

These major codes often have subcodes but they are not displayed. However, knowing the major code often gives enough information to isolate the problem to an assembly. Volume 1 of the maintenance manual has the codes and explains their relationship to the vehicle systems. This is the diagnostics volume. Volume 2 covers how to replace parts.


There are many other aspects of the Graham scanner that support sophisticated engineering studies but I'm renting one primarily as a diagnostic tool ("renting" a loan with a refundable deposit.) A running NHW11 is a lot better to have than having one broken and unrepaired. There are plenty of parts in the salvage yards so there is no reason these cars should not continue service for a very long time.

I will write a separate instruction on efficient driving of the NHW11. Although it will use Graham scanner examples, these less expensive and more common instruments are all that are needed:

* ICE rpm
* ICE temperature

Using the Graham scanner to calibrate these add on instruments would be a clever thing to do and I need it back to keep NHW11s running.

My thanks to Graham Davies for inventing this wonderful tool, Doug Shaffer for pioneering work, and 54,000 NHW11 owners who risked time, money and reputation to make the Prius a USA success. Last but not least are Toyota and their excellent engineers who made this possible ... domo arigato gozaima****a ...

Bob Wilson

ps. I have two Graham scanners and rent one. But the number of NHW11s needing temporary use of these instruments will only increase over time. I make them available as rental units. Contact me by PM.

2019 Tesla Model 3 Std. Range Plus - 215 mi EV
2017 BMW i3-REx - 106 mi EV, 88 mi mid-grade
Retired engineer, Huntsville, AL

Last edited by bwilson4web; 11-26-2009 at 02:07 PM..
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Old 11-26-2009, 01:24 PM   #2 (permalink)
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Very nice, but you're japanese towards the end is a little strange. Using all hiragana would be better. Like this: どうもありがとうございました。

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bwilson4web (11-26-2009)
Old 11-27-2009, 08:58 AM   #3 (permalink)
Engineering first
bwilson4web's Avatar
Join Date: Mar 2009
Location: Huntsville, AL
Posts: 813

14 i3-REx - '14 BMW i3-REx
Last 3: 45.67 mpg (US)

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Thanks: 85
Thanked 212 Times in 136 Posts
Appendix - NHW11 ICE and Vehicle Characteristics

I was planning to write a separate thread about the drag and engine characteristics of the 1.5L NHW11 Prius. However, it makes sense to write it up as a kind of appendix to the Graham mini scanner guide.

Engine BSFC and Vehicle Drag

The following chart shows the Graham mini scanner recorded, Brake Specific Fuel Consumption:

Unlike traditional BSFC curves, this chart uses "bubbles" to indicate the measured, relative efficiency of the 1.5L engine in use ... the operational line. The small red dots are periods of highest engine efficiency. Then come the larger orange dots, yellow, light blue and finally, deep blue. They are plotted showing the ICE torque versus rpm, the operational line gathered from the vehicle operating in traffic. Finally, there are the small green engine HP marks, the measured ICE power output.

This chart uses the drag formula Ken@Japan found to generate the 'power required' line:

The red "HP" line is the dot product of the drag force over the distance per unit of time. It is the amount of power needed to sustain the vehicle at any given speed. The blue "MPG" line is the calculated MPG with a 31% efficient engine and no other vehicle energy costs. The gray "MPG with fixed" adds the measured, vehicle electrical load needed for the control computers, daylight running lights and brakes. To these curves I've added data points from mine and other benchmarks.

Practical Application

Operating the vehicle to keep the engine in the peak efficiency region will provide the best, overall vehicle performance:
  • 1,200 to 2,600 rpm - although in practice, I prefer to keep a guard band so 2,400 rpm is my efficiency peak rpm.
  • 1,300 to 1,650 rpm - high efficiency cruise power, when acceleration is not required.

Drag ultimately dictates how much power is needed at any given speed. So using the "red" HP required line, we can determine how much power is needed at any given speed. Then using the Graham mini scanner derived BSFC chart, we find the "knee(s) in the curve." We simply choose to travel at speeds that stay on the fuel efficient side of these knees.

Now in any given system, there will be subtle 'knees' that are not intuitively obvious. The BSFC chart shows 1,700 to 1,900 rpm suffers a loss of efficiency. This is in the 19-23 hp range and to the left of the knee in the drag based, "HP" curve. It is an area where the vehicle MPG seems 'flat' and not following the traditional V{2} curve. If the engine were more efficient, we would expect a higher MPG value at these lower speeds ... 60 mph is not significantly more efficient than 65 mph.

The more interesting gap is around 2,400 rpm where there is a drop off of red and orange dots. This corresponds directly to the 65-70 mph knee and as the speed increases, the required HP rapidly moves into less efficient engine regions. I treat 65 mph has my normal, cross country, cruise control speed.

One last chart of interest is climbing an 8% grade hill:

Climbing the hill at 55 mph turns out to correspond with an ICE ~2,400-4,150 rpm. Going up the hill faster pushes the engine into the really inefficient regions:

This is a fuel BTU test of different brands in the Huntsville Alabama area climbing an 8% grade hill at 55 mph held by the cruise control. I was surprised to find the vehicle control laws treated 4,100 rpm as a boundary. Neat Easter Egg revealed from the Graham mini scanner data.

Traditional BSFC Charts

The traditional BSFC chart is created by an engine in a dynanometer with a wide open throttle. The dynanometer manages the engine speed, not the throttle, and the dyno measures the generated power. In real world driving, the throttle controls engine power. In some cases, the water pump is not powered by the engine, a little known 'cheat.' In contrast, the Graham mini scannner, BSFC chart shows the operation in urban and hill climb traffic with partial throttle used as needed and includes the water pump overhead.

Similar, field BSFC charts can be produced IF the vehicle has a torque sensor. One approach is to mount sensors on the clutch plate "springs" but this not trivial. Another approach is to mount torsion sensor in a drive shaft or even the wheels but again, these are not trivial tasks. The NHW11 measures torque because MG1 provides the counter torque to the ICE in the power split device.

Bob Wilson

2019 Tesla Model 3 Std. Range Plus - 215 mi EV
2017 BMW i3-REx - 106 mi EV, 88 mi mid-grade
Retired engineer, Huntsville, AL

Last edited by bwilson4web; 11-27-2009 at 10:24 PM..
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