"S" Light: Remaining Solid

1991 Accord EX, F22A4, AT4.

Others of you who have the S Light Issue and have worked on these: does the shift lock solenoid in the Shifter Console stop operation? I've noticed that every time the S Light comes on, the shift lock solenoid stops operation/clacking at the shift lever, and there's no 'click' from under the dash, as there is when the S Light is off/Normal Operation. To research: I jump the service port at passenger side and get no S-flashes (no D4 flashes, neither).

Since mine throws no codes when jumped, and the S light is on solidly, is the issue still within the TCU? I've pulled the cover off the TCU and there're no chemical-burn marks from the resistors & capacitors on neither side of the board being bad and leaking, nor are there short-circuit burns on neither side.

Thinking it might have been a bad Shift Lock solenoid at the shifter, I pulled the shift console off during the last S-light episode and ran a jumper from battery to shift lock solenoid. It clacked and worked as it should every time. Speedo works just fine. Cruise works when S light is on. I adjusted the Throttle Control Cable recently, took out the slack, but starts off in 4th, now. I can manually shift between 2 & 4 on the Shift Console and get 2nd & 4th gear ratios (I know approx rpm @ 55mph), but NO AUTO shifting. Each re-set gets about 500 miles before S light pops on again.

Would these noted symptoms be a Shift Lock Solenoid (lower solenoids on the Tranny) shorting out or failure? Baby's going to a recommended shop tomorrow for checkout, but anyone want to throw a 'Maybe-It's-This' towards me?

Maybe it's the speed sensor. I've seen that before. Hope that it is because that's a cheap repair to make.

I've found a TCU with only 1 digit's difference in them, and this one has an LED in upper left corner, where the one that's in there doesn't. I'm hoping that it works.

Speed Sensor: I thought the tell-tale sign on that was the speedo not working or 'surging' from low speeds up to high speeds, when car is moving at a constant physical speed?

I'd guess it's the TCU, not sure if that TCU will work or not. However, if it doesn't, try a junkyard, ebay, and www.car-part.com you should be able to find one for around $50

So...I put in the junkyard TCU. NO JOY! arrrgggghh. Opened up the case of the junkyard TCU and r41 & r42 are fried to crisps! I opened up the one that was in my car. I have been able to re-set it and get 300 miles or so before the next S-light problem. Looking at it, r42's burning up and r41 is still in good shape. Anyone know what those resistance values are on those two? Neighbor who works as an electric tech at a local mfg plant read the bands @ 150 ohms each. Anyone know if that's the right resistance?

Even if you get the info you're asking for (and I addressed this in your other thread) don't you think there might be a reason the resistors burned up? They don't just give out for no reason, any more than a fuse blows for no reason. So if - and it's a big if - you get the right components and replace them, what are you doing about the root cause?

IMHO you're just setting yourself up for endless fiddling and repairs. Buy a TCU from a junkyard that does their own dismantling. They usually give a warranty (even if it's very short).

But the other possibility that you probably don't want to think about is that there is a problem with the transmission, that's CAUSING the TCU to blow out.

Even if you get the info you're asking for (and I addressed this in your other thread) don't you think there might be a reason the resistors burned up? They don't just give out for no reason, any more than a fuse blows for no reason. So if - and it's a big if - you get the right components and replace them, what are you doing about the root cause?

IMHO you're just setting yourself up for endless fiddling and repairs. Buy a TCU from a junkyard that does their own dismantling. They usually give a warranty (even if it's very short).

But the other possibility that you probably don't want to think about is that there is a problem with the transmission, that's CAUSING the TCU to blow out.

Correct. I had tried to replace the 2 resistors just for experiment purpose. As soon as I turn on the key, smoke came out and the 2 resistors burnt again. There is something else wrong which caused the resistors to burn, a capacitor maybe?

I am not an electrically handy guy. So, if you can find out what is the root cause of this problem, please post it, that will help a lot of people.

If anyone' interested, still: r41 & r42 are .25 watt resistors @ 15 ohms resistance (stripes on the body are: brown (1) green (5) black (zero multiplier or STOP), with gold stripe which represents 5% tolerance), in 28100-PXO-832-M1 computer. That one's mine that hasn't burnt out, yet, but throws solid S after each 300 miles or so. I'd bet the resistors are the same in each circuit board. If your resistance was too high or too low: sizzle, sizzle, smoke, smoke. If one crossed with another printed circuit: Sizzle, Sizzle, smoke, smoke. If tolerance was too low: Sizzle, Sizzle somewhere else on the line; if tolerance too high something in line before r41&r42 would burn.

The Junkyard TCU would be the experimental/sacrificial animal if junkyard guys don't have another to replace it. They wont do a refund and I can't really wait around for another 91 EX Autotransmission wreck to come in. I gotta get cracking on this. The one that I was trying to replace can still be re-set, only r42 has started to turn a dark shade, but the color bands can still be read on it. I can still read the other resistor clearly. Still looks new.

Yeah, I'd probably just disappoint myself in the repair; it's just that it's so close to fix and so inexpensive (6 .25 watt resistors are like $.99 @ Radio Shack and $1.25 for 6 at local electronics repair shop):banghead: .

OHHHHh...I just want to tinker...

www.car-part.com you should be able to find another TCU there.

Tonight, I just replaced a 28100 PXO 832 M1 TCU with a 28100 PXO 731 TCU from a wrecked 91 Accord LX. What happens: In Park: No S Light; in R, no S light, N=no S light; D4= S LIGHT IS ON SOLID, but weak; D3 = No S light; D2=No S Light; D1 = No S light. While in Park, depressing the "S" Switch on the gear selector lever DOES NOT activate the S light for Speed Shift (maybe this came from a DX?). Otherwise, Trans shifts normally and at expected rpm's thru all 4 gears.

SO, as usually instructed when the S-light comes on: I Shorted the Service Port. NO CODES flash. While shorted, the Check Engine light is on solid, not flashing, so I think that the ECU is ok. CEL goes away when the jumper wire is removed. Next, I opened the PXO 731's case. R41 & R42 are OK. No visible burns or shorts on inside of case or on the circuit board, front nor back.

Would this mean this TCU is incompatible with the system of an EX (from DX w/no sport shift mode)? Or is the Shift Position sensor be-fouled?