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Old 16 Mar 2011, 04:01 pm
Join Date: Aug 2007
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Default 1993 Honda Accord flashing "D4" light?

I own a 1993 Honda Accord with 132000 miles on it. The car does have some difficulty starting in the morning, especially when it is cold. Sometimes, even when it does start, it idles poorly and shuts off. However, once it starts, it runs perfectly without any type of problem. Sometimes, after a rough start, the D4 light starts to flash. (along with the check engine light being on). I know this indicates some type of transmission problem, but I have not noticed anything happening while I drive. This happens every 4-5 days, and when I turn the car off and start it again, the lights are off. Any ideas as to why this is happening?
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Old 16 Mar 2011, 04:16 pm
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Posts: 1,338

the D4 light means that the automatic transmission control unit isn't getting a signal that it needs to command the torque converter clutch (TCC) to engage. A TCC that doesn't engage won't have any effect on the way the car drives but it can affect fuel economy and poor fuel economy = excessive emissions = Check Engine Light coming on.

the TCC engages at speeds over 42 miles per hour. IF you drive under that speed you'll never know there is a problem The key input for the transmission control unit is the vehicle speed sensor that 'tells' the control unit the vehicle speed. If the control unit doesn' t 'know' how fast the car is going it will detect a problem and flash the D4 light. In almost 99% of the cases the problem is with the Vehicle Speed Sensor. That part is located on the top of the transmission and is easily replaceable. Yes, there are other things that can cause it, but the odds overwhelming favor a bad VSS on a car that is almost 20 years old.

The speedometer will operate normally when the sensor input to the trans is bad. Also, the rough start has nothing to do with the condition; its coincidental.

Hope that helps
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Old 16 Mar 2011, 04:31 pm
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Join Date: Oct 2007
Posts: 881

Honda Guy pretty much has it dead on."I know this indicates some type of transmission problem, but I have not noticed anything happening while I drive."

Those lights come on for a reason. You should have had the car checked regardless of how it drove, procrastinating just because the car felt fine has now only made your problem worse.
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