Apologize in advance for the long post... I want to give as much info as possible to really pinpoint this issue. I have a good long drive everyday (30mi one way), mostly flat, gives me good opportunity to observe operations and conditions.


Backround: I've previously (1yr or more) replaced failed caps and resistors on TCU, all shifted well after. This recent problem was well mask by other issues already corrected (oil flooded spark plug wells #1 & #2, O-ring leaks [not valve cover seals]), significantly clogged EGR ports (still needing attention, I R&R the EGR valve, and blocked the ports entirely), timing was retarded ~7 degrees. All fixed. I cleaned and sealed the ground under thermostat housing, by the battery, and at the P/S pump. Fluid has less than 5k mi. Prior to this fill, the tranny was flushed manually with approximately 1.5Gal of fluid using the tranny's pump. Fluid is at upper hatch area of dipstick at op temp, no visible foam/bubbles, nor burnt smell; it's nice and pink.


Prior to reaching operating temperature, the car runs exceptionally well, and these symptoms are directly related to reaching operating temperature. The problem is either intermittent, or temporarily corrected by disconnecting the TCU. When the problem is not present, the car shifts great, runs smooth, down shifts appropriately, very little vibration at idle in gear.


Problem: Recently the D4 light has illuminated along with the MIL during startup. It goes out at the same time as the MIL. Up-shifts are normal, but delayed seemingly across the board by 7-11mph. Upon deceleration (coming to a stop), the 3-2 down shift is abrupt, occurring at just under 30mph. Once stopped, the tranny seems to slip into neutral. If I let my foot off the brake, I feel the tranny engage, and the car will no “creep.” If I stop again, I can feel the tranny disengage. While traveling at hwy speed 55-60mph, in 4th gear, the T/C isn't locking up. There is 200-300rpm fluctuations between accel. and deccel. Also, if I floor the accelerator, there is no down shift.


In addition, there are times when the speedo will jerk 8-10mph up or down. I haven't tested, but at parking lot speeds, the speedo doesn't register or registers 2-3mph when I'm sure to be doing 7-10mph.


Last night I finally got the flashing D4 light while driving. Car still shifted the same. Pulled codes, D4 just flashed slowly on---off---on---off, much slower than a blink. After watching for a while it appeared the on/off time changed slightly, but never a blink. (could have been operator error).


Observations: 1. Could the speed sensor be failing in that is reports speed 7-10mph less than actual causing the tranny to delay upshifts, and downshift early, or do the internal shaft/countershaft sensors dictate the shifts. 2. I measured resistance at both solenoid bodies, @60F they all measured around 16ohms to ground (23ohms between them). But from the TCU connector the resistance was ~9.x ohms to ground for each. 3. Assuming the D4 code was a “10”, I checked the resistance of the TW sensor for operation (not to specs). The resistance dropped as the temperature rose. The engine does not exhibit rich conditions, and appears to go into closed loop operation. Are these TCU's sensitive to TW's being out of spec by a few ohms? 4. I've seen reference to the TPS causing issues with no indication, what would my tranny symptoms be if my TPS was failing.


Thanks for reading this far... if y'all have suggestions, I'll give'm a shot and report back.

 

I would remove and clean/replace the vehicle speed sensor. Pretty cheap to replace; ebay, amazon, rockauto.

If this doesn't offer any improvement, I would source a replacement TCU matching your original part number.

good luck

 

Thanks for the tips, that was my intended path. I'll update after I conduct the operations. This trouble shooting would be easier if I could confirm the TCU ignores the speed sensor prior to the engine reaching operating temperature. Oh well, I may figure this out by cleaning the sensor.

 

I know that speed sensor input can dramatically affect shift quality. I had a 97 Acura TL w/ bad speed sensor, and 1-2 would rattle your teeth unless you let off the gas until speed sensor was replaced. Hope this is your problem.

good luck

 

Speed Sensor: Removed two 10mm bolts from the metal speed sensor housing. Once removed, the sensor was disassembled by removing three Phillips head screws. Care must be taken when separating the two halves so the gasket isn't damaged. There is a reusable square shouldered gasket sealing the plastic electronic sensor its metal housing. Inside the housing is a permanent magnet disc, mounted to a shaft, which is engaged by a coupling on top of the transmission. Inside the shaft is a spring with a metallic plug which contacts the plastic sensor side. On the metal housing side of the shaft are two washers, a smaller round one, closest the housing, and a larger round one with 4 notches around its diameter.


Observation: This item appeared to be greased internally, along with grease between the sensor and transmission. I'm not sure of the original type of grease, I would venture to say lithium. What ever it was, it now was substantially dried out, with water contamination over time. That unique stench smelled in cars at junk yards was strong. A sour/musty smell. The grease was “cracked” like mud in a dried pond. It was black in color, and covered the magnetic rotor and pickup sensor. All parts were cleaned with xylene. I didn't have any lithium grease on hand, and felt axle grease was to thick for the light mass of the rotor. I used Wurth HHS-2000 on the internal parts, and standard axle grease between the sensor and transmission.


Results: The D4 light continues to illuminate in conjunction with the MIL upon startup... goes out when the MIL goes out. Reset the memory by removing the 7.5amp fuse. Allowed engine to reach op temperature and drove. Regained light throttle shifts (no longer hangs in 2nd). Down shifts have returned to normal and barely perceivable. Also, depressing the throttle initiates down shifts. No speed abnormalities have been observed in two days of driving, the D4 light also has not flashed.


T/C was still not functioning. Adjustment to TCC effected operation, and appears to be a factor in its lack of functioning. After some adjusting, I've got it locking, still needs tweaking because depressing the throttle lightly at 60mph results in a slight rpm rise, then locks. Also under moderately heavy acceleration from a stop, up shifts exhibit a mild shift flare. Off topic, but related to the original symptoms.

 

Good work.

I've also opened and cleaned a VSS, but never re-installed since I had new replacement. On the 94 Accord reaching the VSS is tedious (one bolt nearly inaccessible) so I didn't want to find out that cleaning was not effective. Not much to go wrong w/ VSS except a little grease obstructing the pickup coil or coil suffers an internal fault.

good luck