1991 Honda accord wouldn't shift into 1st or overdrive. Tcu was bad so I got replacement unit and was told to check solenoids to see if they could have caused tcu problem. Is this true-if so how do I check or test them? Can it be done without dropping pan off the transmission to access them?

Can be a few things. 1) Check the shift solenoids on top of the transmission (front). Remove them and clean out the screens. This would mean your transmission fluid is over due for changing. 2) Maybe it's the Vehicle Speed Sensor (VSS), locate and change that. It's on top of the transmission back under the thermostat area. 3) It could be your Transmission Control Unit (TCU). It's under the floor carpet on your passenger side near the firewall. There is a metal plater covering your ECU and your TCU. The TCU is the smaller box. Remove it, open it and look for burnt items. If you're handy you can replace those items. If you are replacing the unit, make sure it is from a known good one and it matches your car exactly, ie: EX, LX, DX, SE, sport shift button present?, etc... on the circuit board.

Below is a picture of the TCU opened up, here are the transmission codes that your car can display if you are inclined to jump the OBD wire plug to get the reading.

TCU Codes:

CODE LIST:

1-Lock-up solenoid 'A' circuit open or shorted.
2-Lock-up solenoid 'B' circuit open or shorted.
3-Throttle Position Sensor circuit open or shorted.
4-Vehicle Speed Sensor open or shorted - No signal from speedometer.
5-Shift Lever Position Switch circuit shorted.
6-Shift Lever Position Switch circuit open.
7-Shift Solenoid 'A' circuit open or shorted.
8-Shift Solenoid 'B' circuit open or shorted.
9-Counter shaft or transmission speed pulse generator open or shorted.
10-Coolant Temperature Sensor open or shorted.
11-Engine RPM (Ignition coil signal) open or shorted.
12-(No code 12 used)
13-Main shaft speed pulse generator open or shorted.
14-Linear (line pressure control) solenoid open or shorted.
15-Kick down switch circuit shorted.

tune the engine...bad jgnition parts can cause the trans to shift improprerly...my 4 cyl. camry was not going into 1st gear or studdering on first.. corrected with tune-up and cleaned egr valve.. found a lot of carbon in intake manifold.. also replaced canister purge from tank to intake...still need to correct carbon ...but car shifts perfectly.!!!

You will need to have the Tranny checked to see if it is a TCU or a bad solenoid in the Tranny.

HI. This is a TCU fault. This is intermittently occurring at this time, but it will eventually get worse. You will need to have the TCU scanned for possible transmission trouble codes. I suspect that the TCU will need to be replaced or there may be an issue concerning the solenoid pack. You will need those codes to know for sure.

TCU - Transmission Control Unit

No, those sensors are seperate from transmission, should be a solenoid that is electrically controlled inside the transmission that controls the shifting.

does it shift through it's gears? 1st ,2nd,3rd? if it dosn't then the tcu is burned out a common problem for 91-93 accords

Check lights on shift indicator. If missing or blinking, replace shift solenoids. If not that then replace TCU under passenger seat. Don't forget to flush those Honda trannies

Hello marquesevond ..

It may be related to the transmissions electronic control unit. The most common symptom would be that from a dead stop the vehicle feels like it starting out in high gear. The transmission computer or TCU (transmission control unit) suppose to control the automatic upshifts an downshifts but may not be downshifting the trans back to first gear. To verify if this is the problem try shifting the transmission like it was a manual shifted transmission. From a dead stop start off in 1st an manually shift. When slowing down, shift down manually just like it was a manual transmission. On a turn you should be in 2nd gear or 1st manually with your hand shifter depending on how fast you are going. If it drives and shifts good, without stalling, you may have a bad TCU to diagnose.

it is the Transmission Control Unit. you have to find the reason why the TCU is flashing the D4 fault code. not replace the unit. have your vehicle scanned for another code. your transmission or transaxle is giving you a warning that something is wrong .

new tcu