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Provided by Fat Daddy66

I posted this information in bits and pieces before, but I decided to do a complete write up on how to pull the trouble codes from the TCU.

If anyone has put in an aftermarket stereo, and was wondering what in the hell that metal box is behind the stereo, this is the TCU. The TCU controls the various functions of the transmission.
The TCU is a lot like the ECU. When the ECU detects a problem, it will light up the check engine light. When the TCU detects a problem, it will light up the O/D light. Just as you can turn the screw on the ECU to pull a trouble code, and find out what the problem might be with the engine; there is a procedure you can follow to pull the trouble code from the TCU to find out what the problem might be with the transmission. Below is the procedure you need to follow to pull the trouble code from the TCU.

Move the selector lever to the "P" position, and warm up the engine to normal operating temperature. Turn the car off and wait at least five seconds. Turn the ignition switch on (with out starting the car.) Your O/D light should come on. If it does continue with the steps below. If it does not, you have a problem with the TCU power or ground circuits.

Be sure to follow these steps EXACTLY as listed below or you will have to start all over.


1) Turn ignition switch to acc position.
2) Move selector lever from "P" to "D"
3) Turn ignition switch to the on position (do not start car)
4) Depress and hold the overdrive control switch in the "off" position (O/D light will come on)

(If after this step your O/D light does not come on, you have a problem with your Park/Neutral Position (PNP), Overdrive Control, or Throttle Position Switch (TPS) circuit.)

5) Turn ignition switch to off position
6) Turn ignition switch to on position (do not start car)
7) Release the overdrive control switch (O/D light will be off)
8) Wait two seconds
9) Move selector lever to "2" position
10) Depress and release the overdrive control switch (O/D light will be on)
11) Depress and hold the overdrive control switch (O/D light will be off)
12) Move selector lever to the "1" position
13) Release overdrive control switch
14) Depress and release the overdrive control switch (O/D light will be on)
15) Depress and release the overdrive control switch again (O/D light will be off)
16) Depress and hold the overdrive control switch (O/D light will be on)
17) Depress acellerator pedal fully and release
18) Release the overdrive control switch (O/D light will begin to flash)

Now the light should flash ten times. Below is a list of trouble codes for the TCU.

Ten flashes of equal length=Everything OK

First flash longer than the others=Vehicle Speed Sensor(Revolution Sensor)

Second flash longer than the others=Vehicle Speed Sensor Meter

Third flash longer than the others=Throttle Position Sensor

Fourth flash longer than the others=Shift Solenoid Valve A

Fifth flash longer than the others=Shift Solenoid Valve B

Sixth flash longer than the others=Overrun Clutch Solenoid Valve

Seventh flash longer than the others=Torque Converter Clucth Solenoid Valve

Eigth flash longer than the others=Transmission Fluid Temperature Sensor And TCM Power Source

Ninth flash longer than the others=Engine Speed Signal

Tenth flash longer than the others=Line Pressure Solenoid Valve
 
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