Some time ago I began noticing some erratic behavior with my 93 Honda Accord transmission. The problem turned out to be related to the transmission computer and I was able to fix it myself for only a few dollars.
Transmission Control Unit Problem Symptoms
When I started noticing the problems with my Accord, the symptoms would appear for a short while and then disappear. Some of the symptoms I observed were:
- The lights on the shift indicator would flash, not show the correct gears, or light up both reverse and drive at the same time.
- The car would get stuck in what I suppose is third gear, meaning that it would take off very slowly.
- The car would not shift out of first gear.
Sometimes I would attempt to restart the car at times to make them disappear – this was not reliable. I began to use my Honda Accord repair manual and http://www.techautorepairs.com/transmission.html to attempt to troubleshoot the problem, testing things such as the shift control positioning, throttle control cable, map system, electrical components etc and the shift control solenoids and getting the cars diagnostic codes. I did a tuneup based on the premise that if the car was running poorly it could be sending bad data to the ECU and TCU and causing the problems I was experiencing. After doing the tuneup I was also a able to drive for a week without any symptoms, leading me to believe the problem was solved – but this was not the case, the problems soon returned. I feared the transmission was going out and I would have a big repair bill or that this would be it for my Honda and I would have to get a new car – however, the fact that occasionally the car would run fine made me feel that this was an electrical issue somewhere and the transmission was still good.
I decided it was time to look into the Transmission Control Unit (TCU) to determine if this was the issue. the article at techautorepairs.com indicates that it is common to find a burned resistor and capacitor in these TCUs. To do this job I needed the following tools:
I didn’t have any deep sockets, all of my short sockets would not fit, so I had to purchase a set. I pulled back the carpet and began to remove the TCU with using my new sockets. Getting the connectors out and removing the TCU took a little work, but I eventually figured it out. Once out I took the TCU inside and did the rest of the job indoors.
I removed the cover from the TCU with the screwdriver and located the faulty resistor and capacitor. The problem was pretty obvious at this point because the resistor was burned and the capacitor had leaked – this is the exact issue that was listed as a common problem on the techautorepairs.com website.
I took a trip down to radio shack and picked up the needed components, they didn’t have the same capacitor, so I just got the closest one - The original capacitor was a 220 uf 35v rated at 105 degrees Celsius, the replacement has a temperature rating of 85 degrees Celsius. I got 15 Ohm half watt resistors being uncertain if the originals were 1/4 watt or 1/2 watt. I installed the components and reinstalled the TCU. I ended up replacing two resistors but the second was unnecesary - it tested OK once I had it out of the TCU. I drove for a few weeks with the carpet pulled back so I could monitor it for heat issues since the capacitor has a lower rating – I did not observe and heat problems and covered it back up. I have been driving the car for several months now since this fix and have not had any transmission problems since.