1994 Honda Accord At freeway speed trans downshifts to seco

Tiny
HONDAGUY202
  • MEMBER
  • 1994 HONDA ACCORD
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 214,000 MILES
Hello and thanks in advance for any and all help.
I have a 94 Honda Accord EX with 214000 miles on it. The car runs good, trans shifts smooth for about an hour or 30 to 40 miles of freeway driving. Then on the freeway the trans will downshift in to second gear and stay there, then the next day it starts all over again, runs fine until freeway for an hour. I have tried to test the TCM but get no blinking from the D4 light. The trans oil is a bit brown but no burnt smell at all. I changed the trans fluid with Honda ATF-Z1 trans fluid. I’m testing it now to see if that helps.
Any ideas what it could be and how to test for it?
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Thursday, December 4th, 2008 AT 5:21 PM

6 Replies

Tiny
KHLOW2008
  • EXPERT
Hi hondaguy202,

Seems the TCM is faulty and locking the shift solenoids.

When stuck in 2nd speed, does restarting the engine make any changes?

Did you try locating for fault codes without turning the engine off when it happened?
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Friday, December 5th, 2008 AT 10:40 AM
Tiny
HONDAGUY202
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Restarting the engine has a temp fix for it. The longer it sits the better it gets. No I have not tried getting codes from the TCM at the time of the downshift. Can you just jump the pins any time or will that hurt the system? The TCM was high on my list of what it could be, my though was that after an hour or so some of the IC in the TCM would malfunction and cause the unwanted downshift. Do you know of a way I can test to see if it is TCM/electronic parts or a hydraulic issue i.E. A blown seal for a plug screen or passage that is causing it to go into limp mode.
Thanks
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Friday, December 5th, 2008 AT 12:11 PM
Tiny
KHLOW2008
  • EXPERT
Hi hondaguy202,

You can jump the SCS anytime without causing any harm whatsoever.

Seals, fluid pressure and clutches would not cause it to go into limp mode. Only electrical faults can.

The only way to test if it is the TCM is to substitute 1. You do not have any error codes so it is not possible to test if it is TCM, sensors or solenoids.
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Friday, December 5th, 2008 AT 12:51 PM
Tiny
HONDAGUY202
  • MEMBER
I jumped the 2P connector, swiched on the key and watched the D4 light, but it did do anything. Should the D4 light do something to let me know that it is in test mode?
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Friday, December 5th, 2008 AT 1:23 PM
Tiny
HONDAGUY202
  • MEMBER
Ok I found a better jumper and found so trouble codes
D4 code 15:Disconnected mainshaft speed sensor, shorted speed sensor or faulty speed sensor
Check engine code 22: VTEC Oil Pressure Switch
defective circuit or unplugged / defective oil pressure switch.
But I don't see how ether of those could cause the AT to downshift into second after an hour of freeway driving.
Thank you for all your input.
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Friday, December 5th, 2008 AT 7:44 PM
Tiny
KHLOW2008
  • EXPERT
Hi hondaguy202,

The mainshaft sensor or its circuit might be working when it is cold and after some running it fails causing the TCM to go into limp mode. That is the reason it downshifts to 2nd speed. It could be a faulty TCM causing the circuit failure.

The VTEC malfunction should have nothing to do with the trans. It would affect the performance of the engine only. However engine performance would affect the shifting of the trans.
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Saturday, December 6th, 2008 AT 5:52 AM

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