excellent description of solenoid functioning from the wise Hoppyjim that also suggests that I have an electrical connection issue to research.
Posted by: "hoppyjim"
hoppy1@shaw.ca hoppyjim
Mon Mar 5, 2007 1:54 am (PST)
Only two solenoids control all gear shifting in "D" range.
In "D" range, the #1 solenoid is energized in first gear. Only the #1
solenoid is energized in first gear..
When the upshift to second gear occurs the #2 solenoid is energized.
So BOTH #1 and #2 solenoids are energized in second gear.
When the upshift to third gear occurs the #1 solenoid turns off. So
ONLY #2 solenoid remains energized in third gear.
When the upshift to fourth gear (overdrive) occurs the #2 solenoid
turns off. So NO solenoids are energized in fourth gear (overdrive).
Therefore if a total electrical failure should ever occur, the
transmission always defaults to fourth gear (NO solenoids energized).
This is designed for safety, as fourth gear is ALWAYS safe to shift
to. Acceleration from standstill will be very sluggish in fourth gear,
however the car will still remain quite driveable.
Can you imagine the safety, and over revving problems that could occur
if an electrical failure happened at high road speeds and the
transmission suddenly defaulted down into FIRST gear????? Fortunately,
if an electrical failure happenes, you can still safely drive
thousands of miles in fourth gear, whereas it would be very difficult
to drive a long distance home in first gear.
While driving in fourth gear (NO solenoids activated), slowing down
sufficiently. flooring the throttle, or pressing the "overdrive OFF"
switch will activate solenoid #2, and the transmission will down shift
to third gear. Slowing down sufficiently in third gear, or flooring
the throttle will activate solenoid #1, both solenoids will then be
activated, and the transmission will down shift to second gear.
Slowing down sufficiently in second gear, or flooring the throttle
will cut the power to #2 solenoid (only #1 solenoid remains
activated), and the transmission will down shift to first gear.
Shifting is really pretty simple.
The #3 solenoid is used ONLY for torque converter lock up, NOT for
gear shifting. If #3 solenoid fails, or of a total electrical failure
occurs, the torque converter will not lock up, fuel economy may
suffer, but the car will still remain driveable.
All transmission solenoids open a passage that bleeds hydraulic
pressure away from one end of a particular transmission shift valve,
allowing the hydraulic pressure to exhaust back into the oil pan, and
preventing any hydraulic pressure to build up on that end of the shift
valve. With no hydraulic pressure applied to one end of the shift
valve the spring at the other end of the valve causes it to move
toward the hydraulic pressure end. This causes the transmission shift
valve to move one way or the other, opening and closing appropriate
hydraulic passages, in response to the hydraulic pressure change
caused by the solenoid valve.
There is no fine balancing between throttle pressure at one end of a
shift valve and governor pressure at the other end, as in conventional
transmissions. There is a big spring causing the shift valve to be
held one way when the solenoid is activated and line pressure escapes
out through the solenoid valve bleed orifice. However. when the
solenoid is NOT electrically energized, full hydraulic line pressure
quickly builds up causing the shift valve to move the other way
overcoming the spring pressure. There is no hesitation or sticky shift
valves in this transmission as the shift valve has either full line
pressure or zero line pressure applied to it. The main shift valves
are essentially all computer controlled.
The hydraulic passage supplying line pressure to the end of the shift
valve has a much smaller orifice than the bleed orifice in the
solenoid valve. Therefore the hydraulic line pressure cannot build up
on the end of the shift valve when the solenoid is activated because
it is bled off by the open solenoid valve much faster than the pump
can supply fresh fluid.
Bleeding off hydraulic pressure is the same as creating a hydraulic
leak at the end of the shift valve, so the transmission is somewhat
more efficient when the solenoids are NOT electrically activated and
NOT bleeding off any hydraulic pressure. Therefore in fourth gear
(overdrive) the transmission is very efficient, because NO solenoids
are activated, and therefore no line pressure is escaping from the
ends of the shift valves. Also the solenoids consume some electrical
power when they are activated, causing the alternator to work harder.
Since fourth gear is used much more than any other transmission gear,
this is very sensible both hydraulically and electrically.
The solenoid valve is normally held tightly CLOSED by it's spring
pressure. The solenoid valve is opened only when the solenoid is
energized electrically and the solenoid's armature magnet overcomes
the solenoid's spring pressure. If a solenoid valve leaks
hydraulically, the transmission will respond as if the solenoid was
continuously electrically energized.
If a solenoid fails electrically line pressure will not be bled from
the end of the shift valve. When you bench test a solenoid valve it
should completely seal when it is NOT energized electrically, and it
should leak when it is energized. Apply a 12 volt source to the
solenoid wire and ground, and it should leak hydraulic pressure from
the shift valve. Blow air through the solenoid valve to bench test it.
A solenoid valve will not hang up or clog from accumulating dirt, etc.
because any dirt carried by the hydraulic fluid must pass through a
much smaller orifice to enter the end of a shift valve, so the larger
orifice in the solenoid valve is extremely unlikely to ever clog up.
The solenoid, and it's spring is so powerful that it will not gum up.
In "L" range (selected manually) the gear lever hydraulic valve bleeds
pressure from the "L" shift valve end (same as #1 solenoid valve), so
if #1 solenoid fails, or the whole electrical system fails, first gear
can still be selected manually, however the transmission cannot up
shift electronically to second gear in "L" range if #2 solenoid is
inoperable.
In"2" range the gear lever hydraulic valve bleeds pressure from both
the "L" shift valve and the "L-2" shift valve. Manually selecting
second gear should usually result in second gear.
Therefore when a complete electrical failure occurs (both #1 and #2
solenoids fail to respond), "L" range will still be first gear, and
"2" range will still be second gear, however "D" will become fourth
gear (overdrive), and third gear will disappear, and not be available.
If only #1 solenoid fails to respond electrically, first gear
disappears and becomes fourth gear in "D" range (no solenoids
activated). Second gear will become third gear (only #2 solenoid
activated). All other gears will be normal, as #1 solenoid is
activated ONLY in first and second gears. However you can still get
first gear, and second gear by manually selecting "L" and "2" ranges
with the gear lever.
If only #2 solenoid fails to respond electrically, first gear will be
OK in "D" range, however second gear will disappear and also become
first gear. third gear will disappear, and become fourth gear
(overdrive). All other gears will be normal, as #2 solenoid is
activated ONLY in second and third gears. However you can still get
second gear by manually selecting "2" range with the gear lever.
If a solenoid is not working, it is either defective or it is not
receiving electrical power (same as a light bulb).
Access the wire to the solenoid at the transmission wire harness plug.
Apply 12 volts power to the solenoid pin. If the solenoid clicks, it
is very likely OK, or check with an ohmmeter for solenoid continuity
to ground, if you have continuity the solenoid is likely OK.
Check for power (12 volts) from the computer whenever the solenoid
should be activated on a road test. Connect a test light to the
solenoid wire and see if it lights up. #1 solenoid should be activated
(hot-12 volts) whenever first and second gears are required while
driving in "D" range. #2 solenoid should be activated (hot-12 volts)
whenever second or third gears are required while driving in "D"
range. If there is no power to a solenoid, it is most likely due to a
broken or disconnected wire to the computer. Splice in a new wire and
try it.
It could also be the computer, but these computers are pretty darn
bulletproof. If one solenoid is working, that rules out power supply
problems to the computer, etc.
A damaged wire to the solenoid could result in intermittent, or
erratic shift problems and intermittent electrical problems are always
the hardest to troubleshoot. However the solenoid's electrical circuit
is basically no harder to troubleshoot than a light circuit that
doesn't work or only works intermittently.
A faulty wire is the most likely cause of your problem. Find out where
the problem wire is located between the solenoid and the computer, and
splice in a new replacement wire to bridge the problem wire.
I did a very long and detailed post fully describing the Aisin-Warner
A40E electronically controlled transmissions used in Toyotas, a year
or so ago. I also described how to convert your Toyota automatic
transmission to shift manually with electrical switches on the
dashboard. Look up that old post. It should still be in the club
archives, or some members may have a copy. It has an awfull lot of
information about this amazing transmission. I also identified the
wire harness wire colors between the transmission and the computer in
that post, which will be very handy for your troubleshooting.
I hope you find this post both interesting and informative. GOOD LUCK!
JIM HOPKINS
