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Amedee
Amedee, ASE Master Tech
Category: Car
Satisfied Customers: 21813
Experience:  ASE Master Tech advanced level specialist. Wisconsin certified emissions state inspector
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1990 Nissan Maxima: The auto transmission will not engage..shift

Customer Question

My 1990 Nissan Maxima has a strange characteristic and I have not been able to determine the cause. The auto transmission will not engage in drive. It will however, engage in low 2, I can then shift up to drive.

When driving, it will not shift from 2nd gear to 3rd gear by itself. To hold 65 MPH, the engine is at nearly 5000 RPM. We tried to get the self-diagnostic codes but when I get to read the code, the power light does not flash. We confirmed the transmission will shift into 3rd gear manually. So the problem appears to be with the electronic controls.

The engine was recently swapped out and it was discovered that the ECU and TCU were plugged into the wrong unit. I replaced both the ECU and TCU units with used parts (OEM numbers matched). The engine runs fine now, not the transmission does not. Could this be caused by a defective TCU? Or am I heading in the wrong direction?
Submitted: 7 years ago.
Category: Car
Customer: replied 7 years ago.
Relist: I still need help.
Expert:  Amedee replied 7 years ago.

I think you are on the right track with the ecu! I would rec to try and pull codes with a scanner. YOu local auto parts store may be able to do this for free for you. Let me know.

Maybe you would like to try to pull codes again and see if that helps. Would you like the procedure on pulling codes?

Customer: replied 7 years ago.
That was the path I was planning to take when I get the car back from the transmission shop on Friday. I'll get back to you then.
Expert:  Amedee replied 7 years ago.

Here is the info on pulling codes if you want to try it again.

READING DIAGNOSTIC CODES
The Electronic Control Unit (ECU) monitors several engine sensors and actuators. If a problem occurs the information is stored in the ECU's memory for retrieval.
The codes are displayed by the green and red diodes on the ECU. When the codes are extracted they are interpreted by the number of times the diodes flash.
The red diode will flash "X" number of times, this will represent units of ten, then the green diode will flash "X" number of times, this will represent units of one.
For example, if the red diode flashes once and the green diode flashes twice this should be interpreted as code 12. The codes are displayed in numerical order starting with the lowest and ending with the highest.

EXTRACTING DIAGNOSTIC CODES

  1. Access the ECU from the floor board in front of the center console and position it for observing the diodes.
  2. If the engine does not run, turn the key on and proceed to step #4.
  3. Start the engine and warm it to operating temperature then idle.

graphic

 

graphic

  1. Turn the diagnostic mode selector on the ECU fully clockwise until both diodes flash 3 times then turn the selector fully counterclockwise. The ECCS system is now in mode 3.
  2. If the diodes do not illuminate, refer to ELECTRICAL COMPONENT AND CIRCUIT DIAGNOSIS and perform the ECU MAIN POWER AND GROUND CIRCUIT test.
Customer: replied 7 years ago.
Reply to AMEDEE's Post: I was hesitant to accept your answer because the ECU code has consistently been 55 - no problem. I was hoping for something a little more useful. I have the procedure to get the TCU diag code, but when I get to the end, nothing flashes.
Expert:  Amedee replied 7 years ago.
Wait, Nothing flashes on dash? Or on the tcu? Where, and how are you checking it?
Customer: replied 7 years ago.
When I put the TCU into self-diagnostic mode, I get to step 15 below and nothing flashes on the A/T mode switch.

1. Start the engine and warm it up to normal operating temperature.
2. Turn the ignition switch OFF.
Set the A/T mode switch to AUTO.
3. Turn the OD switch ON.
4. Move the gear selector to PARK.
5. Turn the ignition switch ON. (Do not start the engine.) If the POWER light comes on, continue on. If not then the A/T Control Unit is probably bad. [Light is on at this step]
6. Move the gear selector to the D position while stepping on the brake pedal.
7. Turn the ignition switch OFF.
8. Turn the OD switch OFF.
9. Turn the ignition switch ON. (Do not start the engine.)
10. Move the gear selector to 2.
11. Turn the OD switch ON.
12. Move the gear selector to 1.
13. Turn the OD switch OFF.
14. Depress gas pedal fully and release it.
15. Read the POWER lamp. The POWER lamp will start blinking to indicate the stored codes. There will be ten flashes in all. The way it shows the code is by a long flash.
[Nothing flashes here]
Expert:  Amedee replied 7 years ago.
You very well could could be on the right track with a bad tcu unit. You might be able to get one for cheap at a local auto parts store or even at a junk yard.

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