Help please: Speedometer & Shifting Problems

[Chris-H]

Hi;

I have one of those 1990 Q45's and its 21 years old. Still runs, but I am beginning to have issues (with I think sensors). I'm an engineer, good with my hands, but not a car mechanic.
My Q45's speedometer one day about 3-months ago suddenly dropped to 0 while traveling 50mph. Then to my surprise it started reading correctly again a few days later. Then it pinned itself against the top 160-mph. Interestingly, it will come off the 160 and read 140 when traveling around 40mph and 120 when traveling at 60mph. Occasionally, it will fix itself for a few miles before either going to 0 or pinning against 160mph.

I have the service manual (small green one). I think there is a mechanics manual (shop) also, but I don't have this one. So many details are missing. I have looked at the speedometer drawings and see that the speed sensor is wired directly to the back of the speedometer module. I read somewhere the speed sensor puts out a pulse train. This is received by the speedometer module and converted to a 0-5v analog that drives the needle. I looked at the drawings of the speedometer and it does not show the module that takes in the speed pulse train and handles it. I also read somewhere that this module also supplies output to drive the transmission shift logic in the module located near the fusebox.

Am I confused because my early 1990 model car service manual does not show output from the speedometer module going back to the AT module? Is the problem with the erratic speed readings likely to be in the speedometer module itself? If so, I will open the instrument panel and go after it. But, I don't want to waste time opening the console to find the problem is elsewhere.

Now, the second part of the developing problem. I suspect the car has not been going to OD for a while. Just yesterday, the car started to refuse to up shift and down shift in the forward drive gears. It will do P,R,N functions fine. Put it in D and it only knows 2nd gear. The shift lever has no effect when manually shifting between 1,2,3,D positions. Could it be in the special mode that protects the trans? However, if so I would expect to see diagnostic error and there is no failure diagnostic in the display ever. The car just runs in one gear all the time.

I looked at the trans fluid. It was so clean I had a hard time determining its level. So I overfilled it (stupid me). I knew better... hard to see. Anyway, I got a syphon and took out the overfill so it should be ok. It looked low... big drops on bottom of stick. But looking real carefully in the bright light it was ok. I believe the fluid was changed a couple years ago. I drive the car carefully watching the rpm since the engine is aging.

So I think my next step is to look at the AT module outputs and inputs while driving and see what they are up to. I have no experience doing this. I do have scopes and meters. Any suggestions to the approach would be appreciated. Any suggestions on where the problem might be would be appreciated. Obviously, if the AT module is telling the transmission to shift (should be able to move the shift lever and see the drive coils change, correct) then I got a transmission failure problem. I might have a AT module failure. Would think the diagnostic would show this?

Some help with suggestions please.
Thank you for this forum... it is very informative and helpful for us amateurs.

Chris

[Lokim]

Check your fuses first. I blew a fuse jumping relays and it happened to be the TCM circuit. It put my transmission into fail-safe mode (2nd gear only.)

As for the pulse-train, find the speedo sensor on the transmission (should be near the tailshaft) and backprobe the connector with an oscilloscope. With the car jacked up in the rear so the wheels can spin, have an assistant run the car in gear and look at your readings. You should get a perfect square wave that changes frequency smoothly with accel. and decel. of the wheels. If that checks out, your problem is elsewhere. If the waveform is wonky, replace the speed sensor.

[Lokim]

P.S. I'm not sure if it is a hall-effect sensor or not, so if it is a three-wire sensor, you will have a 5V ref, gnd, and signal wire. If it is a two-wire, the sensor should generate it's own AC current.

[Chris-H]

Thank you for your help Lokim. Much appreciated.
I located the A/T after studying the manuals for a long while. After a few attempts to get at it I finally figured out that it is under the side carpet on the left front drivers compartment, the manual seemed to indicate it might be in the dash above the fuses... but not so.

According to the diagrams, pins on AT connector are 24(tachometer), 25(rev sensor), 26(turbine rev sensor), 27(speed feedback from speedometer). I tapped into the back of the connector with some CAT-5 solid wire strands. Just took the cover off and pulled out pieces of the wire to use. The wire is small enough and stiff enough that with some effort you can push it and wedge it into the connector pins from the back.

I have a Fluke portable battery scope. I hooked it up and monitored the pins. The results all appeared to be normal.

Here is what I got.
pin24 to ground Positive pulse its period corresponded to the RPM of the engine. This runs the tachometer.
pin25 to 35(sensor returns) Sine wave of 2-5 volts p-t-p that tracks the speed of the car. This is the AT revolution sensor.
pin26 to 35 Sine wave of 2-5 volts p-t-p that tracks the speed of the engine. This is the AT turbine revolution sensor.
pin27 to ground DC signal that is a square wave that tracks the speed of the car. The signal is from the speedometer module (not the speed sensor) and is 0 - 10v level with a period of roughly 30ms at 20mph (was hard to get exact measurement as was driving).

I attempted to use the shift lever while driving around at roughly 20-25mph, but the car refused to shift into any gear including 1st gear. I remember that at almost any speed, when you put the car in 1st, it is immediately obvious.

Guess next step is to look at the solenoid outputs that signal the transmission to shift. See if I can see anything. Will study the manual again. I know there is a table for the outputs. A short tutoring of what significant to look for would be appreciated.

There are 4 solenoid outs
Lockup, Shift A, Shift B, Overrun. I haven't taken the time to figure out how these solenoids produce 1, 2, 3, D, OD, and Rev gears. Wasn't obvious that there is a mechanical linkage from the shift level to the transmission. Assume the transmission is completely self contained and driven by electrical inputs only, on this car. I will attempt to validate my assumption with the manual.

The speedometer is pegged at 160mph plus. I'm pretty sure this is a problem inside the speedometer module itself and it appears to be readout only. I'm assuming this has nothing to do with the AT not shifting correctly.

Also, this 1990 car had a recall on the transmission in 1999. So the transmission was replaced because of recall at that time. The car has 233500 miles on it, the transmission has roughly 140,000 miles on it. I always drive the car with the rpm under 2000, with the rare exception of passing on freeway where it maybe gets to 3500 - 4000 max for a few seconds.

Chris

[Lokim]

You didn't mention whether you checked all your fuses. The one I blew was in the passenger compartment fuse block next to your leg on the driver's side.

[Chris-H]

Fuse check
Yes, I took a voltmeter and checked ALL fuses in the fuse block. All were good. All had 12V on both sides. Checked with car running.

Chris

[Chris-H]

AT Check (First attempt)

I checked the Solenoid outputs. I checked the shift lever inputs.
The shift lever inputs checked correctly. All is ok.

The solenoid outputs are very suspicious. I put the voltmeter on solenoid B output and got 12V when I turned the key on. In a few seconds it went away. I checked A and it was always 0v. I checked B and still 0v. I turned the ignition off, the put the meter on B again and it came up 12V when I turned the ignition on. It shortly went away. This is not ok. I fiddled around on the connector, but my connection was ok. The solenoid output was intermittent.

Now, I started the car and check both solenoids by shifting the car into various gears. With my foot on the break and shifting gears, both solenoid A and B outputs are 0v. I cannot believe this to be correct.

The tables says
1 gear A on B on
2 gear A off B on
3 gear A off B off
4 gear A on B off

This is a grey code where no two relays can change at the same time, the way it should be. And if they are both off, the car remains in 3rd gear (that's what it is doing). Question is, is the AT module bad or is another faulty condition causing this. I'm betting on the AT controller module and am ready to pull it and inspect it. Before I do, someone wishes to ask me to check something else so I don't do double work... would be appreciated.

I double checked pin-4 the supply voltage for the solenoid power coming from a fuse. It is 12v. That is to be expected as I momentarily got 12v on the Solenoid B output.

Chris

[Lokim]

Check all power and ground circuits to the TCM. Make sure you have full battery voltage (less than .1 volts of drop) at all power and ground inputs. If OK, suspect TCM.

[Chris-H]

Problem solved.

I narrowed it down to the AT controller module. It was doing very odd things, like operating for a few seconds and then freezing. Took out the module. Inspected it. It looked ok at first look. Checked the uP chip, it is a Hitachi 6303. Pulled the data sheets on it. Put my scope on the clock, all ok. Looked at /RD and /WR nothing. Started the module, for those who wish to try this it can be power off a battery between pins 9(+12) and 15(0V). With the scope hooked to (0v) battery return I probed a number of the control pins. I found /RST pin floating.

I traced the reset signal back to a 3-pin POR device, looks like a transistor. But there was no continuity, I looked closer and found the trace broken right at the test point between the uP and the POR device. This was puzzling as at first I could see the a little spot on the conformal coating. Further looking, the trace was severed right where it met the TP. Put a jumper in. Power it up and the /RD and /WR lines were active and the /RST line was high... all seemed ok. Installed it back into the car and it all works. I got shifting again.

Only thing I got to do is recheck the AT fluid level tomorrow. It was a bit high. I may have to suck out another 1/4 of a quart. Then all will be ok.

I did notice the use of aluminum electrolytic capacitors on the board. I changed a couple of them because I had the exact replacements. But, the caps were in decent shape even after 21 years. So that is a good sign. I know all the design parameters are super conservative and so the modules tend to last a very long time. However, this is the 2nd failure. I had my fuel pump controller fail 8 years ago around its age of 13-14.

Thanks for the help. Aloha from Hawaii. Hope this document might help someone else who has this kind of problem later on. I was able to locate used AT controller modules on ebay. They were priced at $29.99 and $59.99 for anyone who may need one.

Chris

[Lokim]

See? Power and ground OK = Bad module. Glad to help.

[Skibane]

I had my fuel pump controller fail 8 years ago around its age of 13-14.

Fuel pump controller failure is a pretty common occurrence - often aggravated by lack of maintenance (obstructed fuel filter).

That's some first-rate troubleshooting, BTW!

Welcome to the forums!

[IRVING GRANADOS]

My speedometer stopped working, i change the speed odometer transmitter , and still the same , any suggestions?

[IRVING GRANADOS]

Check your fuses first.

Thanks sir , but my only problem is that I am new , fixing my first car, can you tell me where are those fuses? please , , there is a tons o fuses to check. thanks

[Chris-H]

Irving;
The speedometer is electronic. It runs off a pulse train that comes out of the transmitter, goes to the transmission shifter logic and from there goes up into the speedometer that is in the dash. If you have an oscilloscope can view the waveform going to the dash by tapping into the transmission shifting module located in front of the driver door on the floor. But, the trouble is likely with the speedometer electronics on the instrument panel. It is involved to pull the instrument panel and troubleshoot the electronics that drives the speedometer. Also, the car must be moving to see the pulses. I used a battery oscilloscope to view my signal to the speedometer. My problem is in the instrument panel.

Can you be more precise with your problem?
Does the speedometer just stay on 0?
Does it ever go full scale or do anything else?
The fuse that powers the speedometer module also powers many other things in the instrument panel. So you should notice if there are other devices not working.

Chris

[IRVING GRANADOS]

Irving;
The speedometer is electronic. It runs off a pulse train that comes out of the transmitter, goes to the transmission shifter logic and from there goes up into the speedometer that is in the dash. If you have an oscilloscope can view the waveform going to the dash by tapping into the transmission shifting module located in front of the driver door on the floor. But, the trouble is likely with the speedometer electronics on the instrument panel. It is involved to pull the instrument panel and troubleshoot the electronics that drives the speedometer. Also, the car must be moving to see the pulses. I used a battery oscilloscope to view my signal to the speedometer. My problem is in the instrument panel.

Can you be more precise with your problem?
Does the speedometer just stay on 0?
Does it ever go full scale or do anything else?
The fuse that powers the speedometer module also powers many other things in the instrument panel. So you should notice if there are other devices not working.

Chris

thanks Chris, the car works fine, the speed odometer is on 160hpm , it goes until 110 mph when the car is working. i just replace the speed odometer transmission sensor , and still the same , so now i will wait , there is a 1994 q45 in pick n pull . but I am not sure if the SPEEDOMETER CLUSTER are the same, so far that's my only problem i have , is there any particular fuses to check????
my cars has 152324 miles , and i want to fixed ;-) thanks for you time , it really helps a lot thanks again

[Chris-H]

Irving;
My speedometer has a very similar problem. The speedometer is at 160 all the time. When I get to around 45MPH, the speedometer comes off the 160 and reads backward. When I'm at 60 it reads 120. If I decrease speed, it reads higher... but when I slow down to around 40 it pegs at 160MPH. If I go faster than 60 it decreases in reading to 110. 105, 100...etc
Occasionally, it will bounce around and read correct for a few minutes. It always returns back to the condition of reading 160MPH full scale. I am planning to pull the instrument panel when I get time and attempt to figure out what is wrong. I suspect a broken ground. It might be a bad IC or component. Let me know how you progress on the fix. It is fairly difficult to pull the instrument panel. From what I understand there are no shortcuts, the dash has to come out from the left area to the gearshift housing (including around radio, AC) area. Although it supposed to come out in one piece, there is a lot of stuff behind all that has to come out. Unfortunately not as easy as just pulling a couple of screws and slipping the instrument cluster out.

Let me know how you progress and if you discover any shortcuts in the removal of the dashboard.

Chris

[IRVING GRANADOS]

Irving;
My speedometer has a very similar problem. The speedometer is at 160 all the time. When I get to around 45MPH, the speedometer comes off the 160 and reads backward. When I'm at 60 it reads 120. If I decrease speed, it reads higher... but when I slow down to around 40 it pegs at 160MPH. If I go faster than 60 it decreases in reading to 110. 105, 100...etc
Occasionally, it will bounce around and read correct for a few minutes. It always returns back to the condition of reading 160MPH full scale. I am planning to pull the instrument panel when I get time and attempt to figure out what is wrong. I suspect a broken ground. It might be a bad IC or component. Let me know how you progress on the fix. It is fairly difficult to pull the instrument panel. From what I understand there are no shortcuts, the dash has to come out from the left area to the gearshift housing (including around radio, AC) area. Although it supposed to come out in one piece, there is a lot of stuff behind all that has to come out. Unfortunately not as easy as just pulling a couple of screws and slipping the instrument cluster out.

Let me know how you progress and if you discover any shortcuts in the removal of the dashboard.

Chris

I'm still with the same problem , i just replace the rack n pinion (used one very good condition ) + power steering pump ( used one too ) now i have a worst problem , i also replace the cluster (used one) no money for a new ones ,
the wheel of the car is hard, and sometimes goes well, also the speed odometer works and then goes back to 0 ...

:-0)

[Chris-H]

I still have the same problem with my speedometer. I have not pulled the instrument panel. Your messages seems to say you didn't completely fix the speedometer problem? "speed odometer works then goes back to 0 ...", does this mean it is fixed or that it incorrectly goes back to 0? Can't tell from your post.

As far as the steering being hard, this is not related to the instrument panel. This is likely the power steering pump install. There is also a bypass switch that changes the power steering feel at higher speeds. This can make the steering hard at slow speeds if it is not working properly. You will still have power steering. If the power steering fails, you will know as it is extremely difficult to turn the steering wheel. This problem is a hydraulic problem related to pump, fluid, or another part of the power steering system. I'm not an expert on this, so maybe another moderator can step in and give you some more specific advise. Good luck.

Chris

[IRVING GRANADOS]

thanks Chris , where is the bypass switch? or what kind of color>? i thinking to go get it , there is like 3 good q45 at the junk yard , can you tell me more details? there is no moneyto buy a new parts the car is old but i love it , thanks and have a nice weekend
also the speed odometer some times when i turn the car on and drive it goes good after a few miles it goes to 0 , i been replace 3 times a speed odometer sensor ( not new ) and still the same . im thinking i might buy it new one but that's the last part i will buy ;-)
irving