The following ONLY occurs during wet weather:
I have a 92 Honda Accord LX with automatic transmission. Starting
from a stop, the car feels as though it's trying to start in third
gear. Once we get going, I cannot seem to get it to go beyond third
gear. On the highway, I can't go past 50 mph, and the tachometer
stays around 3. I noticed that with the engine running and while at a
stop, if I shift into other gears, the D4 light on the dashboard
remains lit (i.e., if I shift to reverse, the R light and D4 light are
lit). The car moves in the correct direction while in the other
gears, but the D4 light stays on.
I think the Transmission Control Module (TCM) is bad, but I wanted to
get others' opinions. Is there a way I can test if the TCM is bad?
Do you have any other ideas of the problem?
You must determine if the TCM thinks it has a problem. Find the module and
watch the lamp in the window. Note the number of flashes, if any, when you
turn the ignition on. On my old Prelude the module is under the carpet where
a passenger's left foot would rest. Pull back the carpet to see the
It's likely that the TCM is sensing some moisture-related problem under the
hood. The number of lamp flashes indicates the location.
I had almost exactly the same problem (91 Accord), except the gear indicator
showed the selected gear, and my 'S' light was on. (Actually, the 'S' light
would wink out sometimes, and the car would drive normally. Then, it would
come on, and the transmission would go into 3rd gear.) It seemed to be
related to wet weather.
Here are some links that may help - or not :)
http://www.honda-tech.com/zerothread?id 2851&postid3094332 (old, some
After reading some advice on the Internet, I came to the conclusion that the
TCU was bad. Some of the literature suggested it was worth a try to fix the
board itself. So I removed the TCU and exposed the board. Sure enough, there
was a bad capacitor, as evidenced by some obvious leakage onto the circuit
board. I bought a replacement at Radio Shack for $1.50, unsoldered the old
capacitor, cleaned the board as best I could, and soldered the new
replacement in. That did the trick, and that repair has held for about 5
If you feel adventuresome, I suggest you remove the TCU and look at the
circuit board. If you find an obviously bad component, try replacing it.
(Leaky capacitors are one thing - you can still see the specs on the side;
burnt resistors may totally obscure what they were, as you cannot see the
colored bands.) Chances are, you have not much to lose, since a rebuilt TCU
will probably cost about $150.00.
-- R Flowers
Dear R Flowers,
Your reply is so helpful since you experience similar symptoms as what
I have described. Last night, I removed the TCM and stared at the
board for quite some time. I could not see anything noticeably
damaged. I went ahead and ordered a rebuild TCM, and I plan to
install it tonight. Would you happen to have an idea why these
symptoms occur during wet weather? The area around the TCM and the
TCM itself were dry. Thanks again for everyone's help!
Moisture is unlikely to affect the control module. The circuit board is
covered in a sealant to block the effects of humidity. What code was the
board flashing, if any?
I've revived TCMs by replacing the electrolytic capacitors at a cost of just
a few dollars. The tantalum and polystyrene capacitors are unlikely to
deteriorate. Note that the electrolytic capacitors used are 105 degree C
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