I think I have a bad TCU (1991 TCU on a 1993 Q45)

[Infinitiguy19]

I got a new TCU from the parts car, I think its bad because the cruise control AKA ASCD doesnt work and the steering is hard to turn.

I understand that the TCU is linked to the ASCD but not the power steering so why is it so hard to turn?

Under the old TCU the steering turns smother than milk.

The car was sitting for 1.5 years, So is there an internal battery on the TCU?

[Q451990]

No battery that I'm aware of...

Heath

[maxnix]

Why would one install a non-first gear starting TCU into a 1993? It's always the other way around.

[Infinitiguy19]

Well up here in New England we have bad winters so the safer (less wheel spin during snow/ice) the better.

Plus it make me feel like I have more power because with a first gear start you have more power all the time, but with the 2nd gear start when you do a WOT run its just feels better.

[maxnix]

Plus it make me feel like I have more power because with a first gear start you have more power all the time, but with the 2nd gear start when you do a WOT run its just feels better.

Ah, Barry Manilow tuning (Feeeeliiinnngs.....)

But at WOT from a standing start, all TCU start in 1st.

[Infinitiguy19]

Ah, Barry Manilow tuning (Feeeeliiinnngs.....)

I will go with this one.

So do you know what it might be?

[Q451990]

Does everything else, like the speedometer and tach. work? Did you run the self diagnostic with the dash? If the TCU is functional enough to give you a result, you might know what input it's not getting... maybe a damaged pin or two on the connector?

Heath

[Infinitiguy19]

Connector is fine.

I was able to see the box next to the AT-Check once but after that it just went back to AT-Check with no box.

I will check the connector and open up the TCU to see whats going on.

What would explain the fact that the steering is hard to turn though?

O wait would that have anything to do with the speed sensor input that could be bad on that TCU?

[Q451990]

My guess is that the TCU passes a signal through to the P/S control unit - but I can't find anything in the FSM that says that's the case.

Heath

[Infinitiguy19]

Yea neither did I that's why I was asking the pros.

O Denis Where are you.

[Q451990]

Probably sleeping... like I should be.

Did your car have body damage in that area? Water in a control unit can cause all kinds of werid problems. Honestly, I have never heard of a bad TCU, but beating the hell out of one with some crumpled metal or short out some parts that feed it and all bets are off.

Heath

[Infinitiguy19]

Well the sunroof was leaking but there was moisture build up on the inside of the car. Plus it was sitting for 1.5 years.

And yea the usual rust spot (rocker panel part closest to the wheel) is rotted not just surface rust.

But I will check the ECU as well.

I am just glad that the car besides the rot spot and the bad sunroof motor is in good shape.

[Infinitiguy19]

Ok I opened up the TCU and it looked fine all the connections are fine (connected) and the board isn't burnt. just that the outside is a bit rusted on the corner.

BUT, with this TCU whenever I press the shifter button (to put in gear) I hear a clicking noise by the TCU, with the previous TCU I heard no such noise.

And the fact that the steering is hard to turn.

I can post High quality pictures if required.

[Q451990]

When you say push the button... you mean the one in the middle of the shifter that you press down with your thumb... not the "shift lock" button - right?

In any case it might be worth just tossing this one if it's not working - assuming your original one always works, and this one always does not.

The clicking you hear is the shift lock interlock solenoid - the part that keeps you from shifting into drive or reverse out of park unless your foot is on the brake. I hear that noise sometimes - but normally when it's cold and when you press and release the brake pedal while the car is in park.

Heath
Modified by Q451990 at 1:03 AM 10/8/2008

[maxnix]

In any case it might be worth just tossing this one if it's not working - assuming your original one always works, and this one always does not.

And this thread can die a much needed death.

[Infinitiguy19]

And this thread can die a much needed death.

I hope your happy its in the trash.

But Whats weird is that with this ECU I got farther into the AT-CHECK Than I did with the original or the other 94 TCS Cali ECU.

What I Mean by further is that I actually saw the little box next to the AT-CHECK screen but thats it, It just stayed at AT-CHECK.

[Infinitiguy19]

OK, I think I found what the cause of the problem WAS. I think the TCU couldn't communicate correctly to the power steering comp because it was of a newer kind or the power steering comp is bad.

Hope that the TCU was the bad one though.

Q45 Tech if you find any of this incorrect please feel free to politely correct me.