John Bennett
06-04-2009, 09:15 AM
How to repair the Automatic Transmission Control computer/unit on a 1991 Honda Accord for under five dollars.
I had to do mine, so I figured I'd write it up and share. Hope this helps someone.
Archived with photos at: http://people.consolidated.net/etrider/accordtcufix.html
Car Symptoms:
- "Sport" light on dashboard stays on
- Clutch won't fully lock-up in 1st gear when shifter is in D4, in other words, clutch appears to "slip"
- Car will not shift out of second gear.
The Cause:
Bad capacitors were installed Transmission Control Unit / Computer (TCU) in this year-range of Accords. As they age, the capacitors leak goo onto the TCU circuit board, causing it to fail. The transmission control computer defaults into "limp mode" which causes the symptoms above.
The Fix:
Replace the bad electronic components in the TCU, or order a rebuilt unit.
How:
Remove the Transmission Control Unit (TCU) from the car. It is located under the carpet in the floorboard where the passenger puts their feet.
Photo 1, Pull the plastic off the passenger side door jamb. It should pop right out.
Photo 2. Pull off the kickplate
Photo 3. Pull the carpet back to expose the cover plate for the Engine Control Module / Automatic Transmission Control Unit (ECM/ATCU). Use a 10mm deep socket to remove the four nuts indicated by the arrows.
Photo 5. Unhook the two electrical plugs in the bottom of the TCU.
Photo 6. Pull the right side of the assembly out and lay it flat on the floor to expose the back side of the unit. Remove the three 10mm bolts shown by red arrows in the photo below to remove the TCU.
At your workbench, remove the Phillips head screws which hold the TCU together. The cover/box should then seperate easily. Inside we see the circuit board.
Photo 7. The red arrows show the leaking capacitor and burned resistor on my unit. Your unit may have more extensive damage, or less.
The leaking capacitor on my unit was a 330 microfarad (μF), 10 volt capacitor. The burned resistor was a 15 ohm. Information about how to decipher the colored markings on resistors can be found here... http://en.wikipedia.org/wiki/Electronic_color_code
Photo 8. Edge view of the burned resistor (left), and leaking capacitor (right).
Photo 9. What it looked like underneath the capacitor.
Photo 10. At Radio Shack I purchaced a pack of 15ohm resistors for 99 cents, and a 470μF, 35volt capacitor for $1.39. This is not the correct capacitor, but it was the closest value capacitor they had.
Next I removed the old capacitor and resistor using my soldering iron. I cleaned away the old capacitor goo with rubbing alcohol.
Photo 11. Then I installed the new capacitor and resistor.
I put the TCU back together and reinstalled it in the car.
To clear any faults in the computer, I unhooked the negative battery terminal for 20 seconds.
I kept my fingers crossed as I cranked the engine. Hooray! The "Sport" light stays off. The clutch locks up. It shifts as it should. I'm on the road again.
A month later I achieved my goal of 200,000 miles.
I had to do mine, so I figured I'd write it up and share. Hope this helps someone.
Archived with photos at: http://people.consolidated.net/etrider/accordtcufix.html
Car Symptoms:
- "Sport" light on dashboard stays on
- Clutch won't fully lock-up in 1st gear when shifter is in D4, in other words, clutch appears to "slip"
- Car will not shift out of second gear.
The Cause:
Bad capacitors were installed Transmission Control Unit / Computer (TCU) in this year-range of Accords. As they age, the capacitors leak goo onto the TCU circuit board, causing it to fail. The transmission control computer defaults into "limp mode" which causes the symptoms above.
The Fix:
Replace the bad electronic components in the TCU, or order a rebuilt unit.
How:
Remove the Transmission Control Unit (TCU) from the car. It is located under the carpet in the floorboard where the passenger puts their feet.
Photo 1, Pull the plastic off the passenger side door jamb. It should pop right out.
Photo 2. Pull off the kickplate
Photo 3. Pull the carpet back to expose the cover plate for the Engine Control Module / Automatic Transmission Control Unit (ECM/ATCU). Use a 10mm deep socket to remove the four nuts indicated by the arrows.
Photo 5. Unhook the two electrical plugs in the bottom of the TCU.
Photo 6. Pull the right side of the assembly out and lay it flat on the floor to expose the back side of the unit. Remove the three 10mm bolts shown by red arrows in the photo below to remove the TCU.
At your workbench, remove the Phillips head screws which hold the TCU together. The cover/box should then seperate easily. Inside we see the circuit board.
Photo 7. The red arrows show the leaking capacitor and burned resistor on my unit. Your unit may have more extensive damage, or less.
The leaking capacitor on my unit was a 330 microfarad (μF), 10 volt capacitor. The burned resistor was a 15 ohm. Information about how to decipher the colored markings on resistors can be found here... http://en.wikipedia.org/wiki/Electronic_color_code
Photo 8. Edge view of the burned resistor (left), and leaking capacitor (right).
Photo 9. What it looked like underneath the capacitor.
Photo 10. At Radio Shack I purchaced a pack of 15ohm resistors for 99 cents, and a 470μF, 35volt capacitor for $1.39. This is not the correct capacitor, but it was the closest value capacitor they had.
Next I removed the old capacitor and resistor using my soldering iron. I cleaned away the old capacitor goo with rubbing alcohol.
Photo 11. Then I installed the new capacitor and resistor.
I put the TCU back together and reinstalled it in the car.
To clear any faults in the computer, I unhooked the negative battery terminal for 20 seconds.
I kept my fingers crossed as I cranked the engine. Hooray! The "Sport" light stays off. The clutch locks up. It shifts as it should. I'm on the road again.
A month later I achieved my goal of 200,000 miles.