Scary transmission moment 2003 M45

[paranoidjack]

So today I was headed to go fishing and playing around in manual mode, just to milk and shift at 4.5 and shift down for stopping. All of a sudden, no matter what number shows on the dash for gear, rpms are not moving. I realize it's stuck in 2nd. I limped to my fishing spot and said a prayer and an hour later got in and all was fine.

Anyone heard of this on the Y34's? I was going to check the fluid, but in the dark saw it was not even permissible with a 10mm nut blocking the chute.

Thanks,

jack

[Ilya]

Sorry to hear that, glad it worked later though. Hopefully one of our Y34 guys will chime in soon.

[paranoidjack]

This is interesting...found this in the FSM...page at42...perhaps my spirited driving confused the transmission that there was a problem? Time to start saving for a transmission and beat the heck out of it when I get 90% there...

Fail-Safe ACS004HM
The TCM has an electrical fail-safe mode. This mode makes it possible to operate even if there is a malfunction
in a main electronic control input/output signal circuit.
In fail-safe mode, even if the select lever is “D” or “M” mode, the transmission is fixed in 2nd or 4th (depending
on the breakdown position), so the customer should feel “slipping” or “poor acceleration”. When fail-safe mode
is triggered, when the ignition switch is switched “ON”, the A/T CHECK indicator lamp flashes for about 8 seconds.
(Refer to AT-97, "TCM SELF-DIAGNOSTIC PROCEDURE (NO TOOLS)" ).
Even when the electronic circuits are normal, under special conditions (for example, when slamming on the
brake with the wheels spinning drastically and stopping the tire rotation), the transmission can go into fail-safe
mode. If this happens, switch “OFF” the ignition switch for 10 seconds, then switch it “ON” again to return to
the normal shift pattern. Also, the A/T CHECK indicator lamp flashes for about 8 seconds once, then is
cleared. Therefore, the customer's vehicle has returned to normal, so handle according to the “diagnostics
flow” (Refer to AT-45 ).
FAIL-SAFE FUNCTION
If any malfunction occurs in a sensor or solenoid, this function controls the A/T to make driving possible.
Vehicle Speed Sensor
Signals are input from two systems - from vehicle speed sensor A/T (revolution sensor) installed on the
transmission and from combination meter so normal driving is possible even if there is a malfunction in
one of the systems. And if vehicle speed sensor A/T (revolution sensor) has unusual cases, 5th gear and
manual mode are prohibited.
Accelerator Pedal Position Sensor
If there is a malfunction in one of the systems, the accelerator opening angle is controlled by ECM according
to a pre-determined accelerator angle to make driving possible. And if there are malfunctions in tow
systems, the engine speed is fixed by ECM to a pre-determined engine speed to make driving possible.
Throttle Position Sensor
If there is a malfunction in one of the systems, the accelerator opening angle is controlled by ECM according
to a pre-determined accelerator angle to make driving possible. And if there are malfunctions in tow
systems, the accelerator opening angle is controlled by the idle signal sent from the ECM which is based
on input indicating either idle condition or off-idle condition (pre-determined accelerator opening) in order
to make driving possible.
PNP Switch
In the unlikely event that a malfunction signal enters the TCM, the position indicator is switched “OFF”, the
starter relay is switched “OFF” (starter starting is disabled), and the position is fixed to the “D” range to
make driving possible.
PNP Relay
The PNP relay is switched “OFF”. (Starter starting is disabled.)

[szh]

Yeah, this has happened to me on my 2003 M45 (Y34) in the past 12 years - scared the heck out of me the first time! But the car checked out fine at the dealer later.

But, I think I figured out the condition that appeared to cause it - basically, I got stuck in 4th till I turned the car off, waited a bit, and turned it on later.

When I exit highways and drive on city streets, I always move the transmission to the M mode - this sets the upper limit to 4th gear and the car upshifts and downshifts as needed without driver intervention, but maxes at 4th rather than 5th. BTW, I far prefer this programming ("max of 4th when in M mode") than what I think is in the 2004 M45 and the similar era G35's transmissions ... where the car downshifts in M mode when coming to a stop and human driver upshifts are needed when accelerating from the stop!

Anyway, my reasoning for selecting M mode is to avoid going in and out of 5th a lot ... this can happen at low speeds in normal D mode and a bit of acceleration is needed in stop and go traffic. This can cause any transmission to "hunt" the top gears a bit, because the rpm's can get low enough that power/torque may be needed to accelerate ... and the car downshifts often. I am trying to avoid wear and tear on the 4th to 5th changes!

Well, the few times what I call "limp-mode" happened, it was because I think I timed the lever move from D to M at just the moment when the transmission was also probably making a transmission change - perhaps down to 4th or up to 5th coming off the ramp. And this possibly confused the TCU when the control messages arrived "together".

I don't think this is a bug ... more likely, the classic FIFO timing constraint (for those of you EE geeks out there. ) raising its head. Where which came "First" in "FIFO" selection is unclear (purely a theoretical mathematical timing issue !).

Bottom line: since this has happened rarely enough (only a few times in 12 years that I have owned my Y34), I am not too worried about it.

OTOH, if the transmission starts slipping or something, then I will be far more concerned! On my last 1995 Q45, the transmission would not select Reverse and then died, at just about 105k miles ... so far, I am at over 170k on my Y34 and it is still looking good (touch wood)!

I partially attribute this improvement to the steady 30k mile powered flushes ... and perhaps also a better transmission compared to the first-gen Q45.

Also, my 1995 Q45 was a lease return that I bought in 1998 and I suspect that the previous owner had not cared for the car and transmission properly!

Z

[paranoidjack]

That's good to hear. I also love how the 2003's "M" mode is set up....I also use it all the time to decelerate. Feels better for the car, especially the brakes and transmission.

Very relieved. Going to flush this week anyway just to be safe.

Thanks!

[Double E]

I would be cautious about frequently decelerating with the transmission. It's not what it was engineered to do with reliability.
Think of it this way...which one (brakes or trans) is specifically designed to slow the car down and which one is easier & less expensive to replace?

[EniGmA1987]

Well, the few times what I call "limp-mode" happened, it was because I think I timed the lever move from D to M at just the moment when the transmission was also probably making a transmission change - perhaps down to 4th or up to 5th coming off the ramp. And this possibly confused the TCU when the control messages arrived "together".

I don't think this is a bug ... more likely, the classic FIFO timing constraint (for those of you EE geeks out there. ) raising its head. Where which came "First" in "FIFO" selection is unclear (purely a theoretical mathematical timing issue !).

The CAN bus system in our cars is impossible to confuse that way. All messages are received at the same time "always", so both messages would normally arrive at the same time. however the system is set up so each device is hard wired to be a specific priority and so the dominant device will always have it's message received. If both devices say something at once then the lower priority device will shut it's message off and queue it for re-transmit once the more dominant device has stopped sending it's message. You cannot have 2 devices with the same priority on the car's CAN bus network system. Each device, or sensor, or whatever has it's own 11-bit (or 29-bit in some systems) identifier and they all transmit to each other every single frame of the bus system. The bit ID itself says which device is of higher or lower priority in the car's system.