The D4 light

I seem to have a D4 light which sometimes is on (solid) and other
times is not on. At first I thought the LED was failing but then in
the service literature it appears that D4 is used as a TCU diagnostic
readout. Do you think the TCU is trying to tell me something? From
online reading it seems that the "S" light would be lit in the case a
code was stored...

The transmission works fine, under load sometimes it upshifts at
higher RPM than it should, and when shifting under load it flares
(this is most obvious on 4-3 downshift), but it never slips out of
gear or fails to go into gear.

 

Year? Model? Engine? Mileage?

 

I'm sorry, it's a 90 Accord EX, 2.2 SOHC, 200k.

 

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How many times have you changed the tranny fluid, and was the correct
Honda fluid used?

'Curly'

 

The fluid is old. The tranny needs to be flushed. The car sat for a
long time and the motor was repaired. I put a bottle of Lucas in it
after the motor repair to get it by.

I am not that concerned about the rough shifting in and of itself. I
am more curious about what would the D4 light being solid on some of
the time (i.e. normal), and sometimes completely off. Seems like it
should be flashing if there's actually trouble, or the S light would
be on. I tried "wiggling" the shifter but it doesn't seem to be
intermittent. The tranny behaves the same no matter what the state of
the light is.

Maybe it's just a flaky LED in the dash cluster?

 

In your car the "S" light is used as a diag tool.

Your D4 light problem is likely a flaky connection somewhere, probably at
the shift lever. This *may* also account for the odd shifting behavior.
However...

You have 200K on the tranny, and old fluid. Failure to change the fluid
will cause irreparable damage to the clutches and hydraulics of any
automatic. In your case, Dexron-III is OK, but Honda ATF-Z1 is better.

I would have the fluid drained and refilled at least three times with Honda
ATF-Z1. If the transmisison isn't in too bad shape, this may be enough to
cure your flaring problem. If it does not, then you have severely worn
clutch packs, or sticking solenoids.

 

Yeah, I plan to have it flushed via machine and obviously to use the
correct fluid. This question was more trying to figure out if I also
have a TCU gremlin to deal with... I'll check that harness at the
shifter next time I have that apart. I actually just had it apart to
lube the shifter rod and the park pin.

 

DO NOT FLUSH IT!!!

Drain and refill with Honda fluid at least 3 times.

 

NONONONO Noooooo. Do NOT have it flushed. Have it drained and filled, 3
times, with about a week between each time.

 

Interesting. The gospel I've always been handed is that a drain and
refill is the wrong thing to do. The explanation was that changing
the fluid would renewing the detergents, which slowly dislodges the
crud that is built up in the transmission, which then clogs the filter
and starves the pickup. (Which is the point of "transmission fix"
products, to bring back the viscosity of the fluid without adding new
detergent.) The flush, if done properly through the pickup instead of
the cooler lines and using fresh tranny fluid and not solvent, would
get rid of all the old fluid AND crud, to essentially reset the fluid
to a known state.

Maybe the hole in this, and why everyone is recommending repeated
short term fluid changes, is that the crud gets dislodged too slowly
for the flush to actually clean anything out, so it's really no
different than a one-time fluid change, which is a big mistake on a
neglected tranny.

It would be interesting to see what the factory repair manual
recommends, or maybe the 3-time change actually is what they
recommend, anyone know?

 

That's exactly what is recommended by Honda.

Also note that your Tranny does not have a serviceable filter. Just drain
and refill 3 times, and you will be fine.

 

Your transmission is likely already on its last legs and will fail soon.
You have little to lose by trying this.

The drain-and-fill-three-times IS the factory recommendation. You are
supposed to drive the car briefly between each drain and fill.

The multiple fill/drive/drain sequence compensates for the fact that the
torque converter has no drain.

 

Well, if the drain plug is not full of metal I think it should be
okay.

A "new" used transmission isn't that much anyway, freight costs more
than the tranny. Is it possible to drop the tranny out the bottom as
a shortcut?

What is "briefly"? Mileage? Stay off the highway?

 

Clutch lining material does not stick to magnets.

That's the accepted way of removing a transmission. No need to pull the
engine too.

Long enough for the fluid in the torque converter to mix with the new fuid
in the pan. Once around the parking lot should do it.

 

True, but then I should see it floating around IN the fluid, either
way the evidence should be visible.

So then I can get the whole thing done in an afternoon. Now to find a
nice deserted parking lot since my landlord doesn't allow car
repairs...

 

It sort of is. That's what makes the fluid black. Should you start finding
chunks or fragments in the fluid, the tranny's *really* pooched.

I had the same problem when I lived in an apartment. I understand the
landlord's reasoning, but it still makes things more difficult.

And you do know how to check the fluid level in a Honda AT, do you? It's
not the same as most cars.

 

Well, the fluid isn't black, it was still clear on the dipstick, just
more brown than red. Of course it's hard to tell what's going on just
from the dipstick.

I checked it with the motor running after a short drive like my other
cars, but from your comment I'm guessing that's the wrong thing to
do. I made sure that the rubber seat of the dipstick "popped" back in
so the level would not be wrong. I didn't care so much about the exact
level as the condition of the fluid at the time, since it had not been
driven for quite a while and previous owner probably neglected it.

 

As I said before, a fluid change may not help your issue here, but it
certainly won't hurt. This is a cheap first-effort before looking for more
difficult stuff.

I'm suspecting you have deeper problems inside the transmission, either
sticking solenoids, or a sludged valve body.

You SHUT THE ENGINE OFF, then check the level within one minute of shutting
the engine off.

Honda is different. What can I say?

 

Here is something I didn't mention before (because I wasn't really
trying to "solve" the transmission problem, just wondering about the
dash LED). If I stomp on the pedal to where a load based downshift
would be imminent, but then manually shift down into third while
keeping the throttle open, it doesn't flare up. Isn't that strange?

Well that's good to know. They should print things like that on the
underhood label instead of burying it in the owner's manual, IMO.

 

Nope. It narrows things down. You almost certainly have a bad shift
solenoid. A problem like this is supposed to make your "S" light blink, but
I guess that doesn't always happen.

jim beam rigged something up recently that allowed him to observe the
solenoids in operation.

Especially when the other 99% of cars on the road are different from that.