1993 Honda Accord D4 light stuck on

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3 weeks 20 hours ago #203783 by andyknight3
1993 Honda Accord D4 light stuck on was created by andyknight3
Hi everyone,

I recently did a service on my '93 Accord, brakes, oil change, and changed the transmission fluid. Since getting the car back on the road the D4 light on the dash has stayed on (continuously on, not blinking) regardless of which gear I'm in. From a dead stop moving forward but not reverse, the vehicle feels sluggish (almost as if I'm driving with the parking brake on) but once I'm moving it seems to drive and shift fine. I checked for codes but when I jump the connector the D4 light does not blink, it just stays solid. I rechecked the transmission fluid level and noticed it was low, so I added more fluid and now the level reads fine. I disconnected the battery to clear the memory but the issues remain. I've done some searching online but haven't found answers to my specific situation (if the answer is already out there then I apologize for reposting and offer many thanks to anyone who can point me to it) Some people say that the D4 light stuck on is an indicator of a bad TCU but given that I just serviced the transmission, I find it hard to believe that my issue is not related. Thanks everyone for your help.

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3 weeks 5 hours ago - 3 weeks 5 hours ago #203790 by college man
Replied by college man on topic 1993 Honda Accord D4 light stuck on

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Last edit: 3 weeks 5 hours ago by college man.

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2 weeks 5 days ago #203803 by andyknight3
Replied by andyknight3 on topic 1993 Honda Accord D4 light stuck on
College Man,

Thanks for the advice. My concern is that I can't seem to reset the tcu. I tried disconnecting the negative battery terminal, and separately I tried removing the backup and ecu fuses. In both cases, when I turned the car back on the D4 light remained stuck on. I saw the flowchart for diagnosis that was posted in that thread but I'm not sure I can follow it ( I don't really know what "test harness 'A'" is), unless its simply a matter of checking voltage at a certain connector pin. I'm hesitant to just replace the tcu, I don't want to just keep throwing parts at the issue until it goes away, but if theres reason to believe that that's the likely culprit then I suppose I have no option. Thanks again for all the help!

-Andy

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2 weeks 5 days ago #203805 by college man
Replied by college man on topic 1993 Honda Accord D4 light stuck on

andyknight3 wrote: College Man,

Thanks for the advice. My concern is that I can't seem to reset the tcu. I tried disconnecting the negative battery terminal, and separately I tried removing the backup and ecu fuses. In both cases, when I turned the car back on the D4 light remained stuck on. I saw the flowchart for diagnosis that was posted in that thread but I'm not sure I can follow it ( I don't really know what "test harness 'A'" is), unless its simply a matter of checking voltage at a certain connector pin. I'm hesitant to just replace the tcu, I don't want to just keep throwing parts at the issue until it goes away, but if theres reason to believe that that's the likely culprit then I suppose I have no option. Thanks again for all the help!

-Andy


Actually you are correct on checking the voltage. Unplug the TCM connector and check the voltage at pin A8 and body ground.
Have the ignition switch in the start position while doing the test. If the 12volts is seen at that pin the TCM is bad. keep us posted
on your progress.

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2 weeks 4 days ago #203809 by andyknight3
Replied by andyknight3 on topic 1993 Honda Accord D4 light stuck on
Got a chance to take a look this afternoon. I'm getting good voltage at what I think is the A8 terminal (although without a better diagram I cannot be 100% sure). Looks like that means it's time for a new TCU. I'm still a little suspicious that I had a failure at the same time I changed the fluid, but maybe the fluid change and initial low fluid level revealed an issue with the TCU that had long been lurking? I'll go ahead and order the part now and when I get it installed I'll be sure to post back here with the results. Big thanks for your help and patience College Man!

-Andy

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2 weeks 3 days ago #203815 by college man
Replied by college man on topic 1993 Honda Accord D4 light stuck on
Keep us posted Andy.

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2 days 26 minutes ago #203904 by andyknight3
Replied by andyknight3 on topic 1993 Honda Accord D4 light stuck on
I finally got the repaired TCU in the car today. I actually sent it out to David Ruberg ( www.speedometerrepairguy.com/ ) to have my old one fixed as I had trouble sourcing a replacement. I reinstalled it today and so far so good! The D4 light is off and the car dives great. Big thanks to College Man for your help. Hopefully others will find this thread useful in the future!

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1 day 5 hours ago #203912 by college man
Replied by college man on topic 1993 Honda Accord D4 light stuck on
Glad to be of help Andy. Happy motoring.

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