Volvo RWD 900 Forum

My daughter's 960 has been delivered to me for repair. All shifting is "late", by that I mean rpm's will be up very high (3500 or so) before a upshift will happen. This occurs between all gears, even with very light throttle, will only hit 4th at speeds above 65 mph, don't think TC lock up is happening at all. In any gear the slightest bit of throttle pressure will cause immediate downshift.

No fault codes from transmission ECU.
All tests pass.
Fluid clear and unburned. proper level.

I am sure that the transmission itself is OK. I have checked the voltage signals from the ECU to the shift solonoids and the tranny is doing exactly what it is told. In other words the ECU for some reason is telling the tranny to shift late.

This problem is driving me nuts, have checked all sensor inputs related to shifting such as throttle position, speed, rpm, tranny temperature, mode, gear selection and more. Have even disconnected battery overnight with the thought that maybe the ECU's needed to be reset.

Desperate for information and suggestions.
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David Hunter

At least I think I found it. There is a massive air leak at the #2 manifold runner. It can't be seen but I discovered it with a plastic tube to my ear. When I get down under that runner with the tube there is a loud whistle/hissing noise not really audible otherwise. This explains why #2 does not fire at idle, engine fault code 232 and most likely explains a wonky load signal to the tranny.
Walt, you suggested checking vacume, had only 13.5", that quickly led me to the leak. Thank you
Will be installing a new gasket in a day or two.
Will post results.
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David Hunter

Installed new manifold gasket today. Of course engine now runs beautifully, vacume at idle is 18", O2 sensor output transitions as it should, no more smelly exhaust, smooth idle. Shannon and Walt, thank you so much for your suggestions.

The shifting is much better but not where it should be. Have not yet checked the load signal. That is for tomorrow.

Anyone know about ECU "learning". As I understand it means the ECU learns the characteristics of the engine via the sensors and adapts the injector and spark mapping accordingly for best performance. I am sure with what I have done there is some relearning to do. How fast does that happen. I suspect it takes a certain number of trips and temperature cycles. I also suspect that the 'learning" process will have an effect on the load signal.

Walt, Shannon. Anyone?
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David Hunter

Hi David,

Congrats! You are making progress in the right direction.

As far as the ECM learning, it typically (even on our 2007 Toyota) takes at least 2 full tankfuls of driving around for all parameters to be 'learned' by the ECM. Some will happen faster, other parameters take a 'trend' to adjust.

DEWFPO
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1998 S90 083,228 and 1995 964 154,100

Thanks for the input on learning. Since my last post I have swapped the engine ECU, transmission still shifts late as before. No sign of any improvement in shifting as result of learning after about 7 trips/drive cycles.

Had a chance to chat with the lead mechanic at a local Volvo dealer, intriqued by the problem he invited me into the shop and then into his locked back room, the inner sanctuary with the complete library of Green Books, special tools mounted on the walls that we only see in pictures but can never get to have. And yes they do have a secret personal cache of spare parts such as MAF's, ECU's etc for use in diagnosing. He let me loose on the library where I started to read about the how the TCU works and how it talks to the ECU and the tranny itself. He also made an offer to photocopy anything I want. Before I could get too far however word came around that the owner was on his way and I had to leave the inner sanctum and shop area. He invited me back any Saturday morning to hang out and look at the library material.

Here is where I think I stand.
There are 4 main signals that would affect shift points and lock up as the car gains speed:
1. MPH. originates at diff sensor and goes to ABS, speedo, cruise and TCU
2. Throttle position sensor on throttle valve
3. Converter output rpm. (comes from a sensor on tranny)
4. Engine rpm and load. (Combined signal from ECU)
Other inputs are such things as brake signal, selected gear, mode, full throttle switch etc that I have checked and double checked. These are all off/on type voltages that do not directly affect shift points.
I have confidence that all is well mechanically inside the tranny as it simply shifts when told to by the TCU. I know this from watching the voltages to the 4 solonoids.

My prime suspect
now is the speedo signal to the TCU. I am not sure if it is correct. It originates as an AC signal from a sensor on the diff and is sent to the ABS unit, from there it branches off and disappears inside the speedo. Outputs from the speedo go to other places such as cruise control, radio and to the TCU. I do not know if the speedo processes the signal to a DC pulse or just passes it through. I am now pursuing this.

Please..... ideas, thoughts, suggestions from anyone no matter how stupid it sounds, I am in brainstorming mode and will consider anything.
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David Hunter

My research reveals that the speedo head does "process" the raw AC signal originating from the diff sensor. It is supposed to exit the speedo and go to the TCU as a digital pulse increasing with speed. My signal is 1/2 the frequency it should be therefore the shifting is very late. I also read that when the signal is not present the TCM will default to a calculated value for shift points but the shifts will be rough. I tried disconnecting the signal and all of a sudden shift points were more or less normal but of course a fault code is set and the TCM soon shifts to Limp home mode. My conclusion is that the analog to digital conversion in the speedo is bad and will be trying a replacement speedo.

I am going against the advice of several seasoned Volvo mechanics. They tell me to replace the tranny but I respectfully have disagreed with them. I maintain that the tranny is simply shifting when its told to and that the problem is with the electronic control.

Will keep posting progress.












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David Hunter

Thanks for the update David, sounds like you are narrowing things down. Please keep us posted and perhaps write this up for the FAQ's.

DEWFPO
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1998 S90 083,228 and 1995 964 154,100

Ditto!

I just read all the posts in this thread and it comforts me to know there are still such talented resourceful people on the board should I need help.

My '96 965 got a replacement motor a year ago last February and has been trouble free up to now. (Well, I did replace front shocks & springs and driver's seat upholstery but that didn't need any diagnostics.) I also got myself a retirement present of a 2004 Porsche Boxster S so it has become my new "mistress".

My best to all.
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'96 965, 16' wheels, Michelin Pilot Sports, rear 18mm bar + Koni, 201 HP cams, 149K. Put 200K on '85 745 TD.

Installed a replacement speedo head and all is now normal.
This problem was caused by an incorrect digital signal from the speedo to the TCM. The frequency of the pulses which inform the TCM about speed were exactly half what they should have been. I discovered this by running TCM test 5 with the rear wheels off the ground. If speedo said 30 mph the test results said 15. Throughout all my work diagnosing the problem I never had a fault code form the TCM, had there been no speed signal at all there would have been a code. In this case the signal was present it was just giving a false speed.

I wonder how many owners have paid to have a new TCM or worse still a transmission rebuild for such a simple to fix problem.

Congratulations! Man, what an odyssey! At least you stuck with it until a satisfactory conclusion.

Thank you. It was my mission for the last 3 weeks to fix that car. Often you see an apparently good looking car languishing in the back of a lot somewhere because no one can figure out how to fix it. The owner gives up after spending a lot of money. I was determined not to let that happen. We had owned that car since it was almost new. My daughter took it over about 3 yrs ago, she was ready to go out and claim the $4500 government gift and buy a new car. This car is now ready for another 3 yrs. Will be changing the timing belt in a few weeks.
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David Hunter

Great job David, please write this up in detail if you can for others.

Cheers !

DEWFPO
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1998 S90 083,228 and 1995 964 154,100

Since this transmission is completely electric over hydraulic (no vacuum modulator to determine shifts), the TCM gets the inputs from the ECM and determines shifts. Vehicle speed, RPM, throttle position (is a primary input), current gear, engine & trans temp, PNP sensor and E,S,W switch. Sounds like one of the inputs is confusing the TCM. I know mine shifted funny when the PNP was going bad (but not the same as yours). Perhaps you can check the PNP sensor and the E,S,W switch.

DEWFPO
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1998 S90 083,228 and 1995 964 154,100

Walt:
Thanks for your response. Sorry to take so long to get back here. Since I first posted I have swapped out the TCM and throttle position sensor with no change.

No fault codes at plug A1, All tests have passed in Test modes 3 and 4.

Have also tested the following with analog and digital meters:
Throttle position voltage passed from ECU to TCM at Connector B1. OK
Output of (engine) speed sensor on side of tranny at A16 and A17. OK
Oil temp sensor resistance cold and hot at A6 and A7. OK
No voltage is floating on the grounds A 11 and A12
12V supply to TCM is correct at A14 and A30.
Speedo signal at B8. OK

I have even monitored voltages to the 2 shift and torque converter solonoids while test driving (hooked up some LED's to the TCM outputs). The solonoids and resulting shifts are exactly what the TCM commands. Kick down and brake signals OK. I have measured the "handshaking" between the ECU and TCM. All seems OK except I have no idea what the connection at B16 called "load" is for, appears that this never changes value.

Tonight will be double checking all switched outputs from the E,S,W and PNP. I think they are OK as "confusion" here normally sets a code. Am also considering swapping the ECU if my local friendly Volvo shop/junk yard will let me borrow one. I am somewhat lucky that this resource is nearby and I have a good relationship with them.

Let me know if you have any thoughts? Will post back tomorrow.


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David Hunter

David, you've performed very impressive diagnostics. In my book, terminal #16 (it doesn't indicate a B), says it's the Control Signal (STH), system pressure solenoid, freq = 300 hz, frequency is constant independent of driving conditions : The signal duty cycle is modified when the system pressure is adapted.

I would interpret that to possibly mean that as long as the transmission has proper pressure, the wire has a 300Hz signal on it to the TCM, and only changes when there is a gear shift, but I very well may be wrong.

The table of symptoms in my book does not list anything like you describe.

Late shifting as you describe is usually a result of a heavy load on the engine. Big throttle inputs, low engine vacuum. I know you've checked your throttle position sensor already, but have you exercised the TPS with a DVOM attached to see if it's spiking or has a dead spot in it?

Can you measure you engine vacuum? at idle and under load?

I hope you don't mind the brainstorming here.

DEWFPO
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1998 S90 083,228 and 1995 964 154,100

I have limited resources, just a wiring diagram and test procedures.
I welcome the brainstorming and will try anything.
Terminal #16. We are talking about the same point. It comes from the ECM #33, correct? I agree with your interpretation except that I would say the duty cycle changes (frequency stays the same). I presume this signal has to do with the TCM dropping pressure in the tranny for smoother shift by control of line pressure solonoid on TCM terminals 4 and 5.
According to my info ECU and TCM "handshake" on 6 lines. I do not understand much about this exchange of signals with the exception of the B1 TPS. I did see level changes on B5 B6 B7 as it shifts gears but nothing on B16. Did not check B15.
TCM terminal:
B1 Throttle position signal passed through ECU from the TPS sensor.
B5 TCM reponse
B6 TC 1
B7 TC 2
B15 Gear position
B16 Engine Load

I will be checking engine load on B16 again with an analog meter to see if there is any change under driving conditions. I believe the analog meter will move slightly with a change in duty cycle. (Wish I had a scope).

Will measure manifold vacume at the "tree". Does the Motronic 1.8 monitor manifold vacume?

I have checked the throttle position sensor output voltage at the source and at term B1 above. It swings smoothly from about .5V at idle up to around 4V at full throttle, I presume that is normal. Have also measured it's resistance on the bench. Can't remember values but it changed smoothly. These measurements were done with digital and analog meters.

I will add one additional point but do not think it is relevent to the tranny issue. Engine idle is a bit lumpy due to a miss on #2. Smooths out as soon as throttle is opened. Compression, injectors, spark coils and plugs OK. Maybe front ignition module?


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David Hunter

Have rechecked all tests on the TCM. Measured all inputs, outputs, all OK.
The "handshaking" between TCM and ECM seems to work perfectly.

However the "load" signal makes no sense to me. There is no test for this signal. It is ECU connector #39 to TCM #B16. Using my Digital meter I can measure a frequency of 12HZ at idle, this increases in a linear manner with RPM. Voltage is about 380 mv. These 2 measurements I think are normal.
Duty cycle at idle is about 17% but it jumps to 100% as soon the throttle is opened even the smallest amount. This does not seem right.

Now here is the interesting part. Vacume is only about 13" at idle, this seems very low, should it not be higher? Does this indicate a vacume leak? Have checked all lines at the "tree". Could I have a manifold gasket leak? Is this affecting the load signal, causing the lumpy idle, and causing engine fault code 232?

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David Hunter

Hello,

I've read this thread with great interest. I am not going to be much help; I have never opened the hood on a 960. But I understand how things work in general. I hope that my rambling on the subject might give you some new paths to explore.

You might find this interesting:
http://forums.turbobricks.com/archive/index.php/t-35724.html

Reading that, and knowing nothing else about the system, I would check the input from two switches before going further: the input from the brake light switch and the "full throttle" switch. If the TCM thinks the brake is applied, it will assume a braking condition and select the appropriate gear for that mode. There is also a full throttle switch. If it is made constantly the TCM thinks the throttle if fully depressed (regardless of load).

Regarding your checks, the change in duty cycle at the load sensing input should give a slightly higher DC value. Wider pulse widths produce an effective increase in DC that a meter "sees". For instance, a 5V high and 0V low, at 50% duty, has an effective DC value of 2.5V. If the DC value shifts with load, that is confirmation that, if not correct, at least a change in load is producing a change in duty cycle. The value you see will depend on the meter you are using. The Fluke 88 is pretty fast and will read out close. A cheap meter may not give an accurate read out but should at least show some change.

The fact that you can see no change on the load sensing line is important. If I correctly understood that explanation of how the AW30 shifts, shifts are initiated by the TCM dependent upon the speed of the planetary gear. The TCM issues a request to the ECM to reduce torque (for smoother shifts) and awaits confirmation from the ECM that torque has been reduced (pulled the timing back?). It will then modulate pressure for the shift.

For that miss on #2 at idle, check for an air leak at the intake/head gasket.

Good luck and post the fix for this. I'm interested because I love puzzles. Someday I might own a 960 and it might come in handy. Man, I wish I had a copy of Vadis...

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Mr. Shannon DeWolfe -- I've taken to using mister because my name misleads folks on the WWW. I am a 53 year old fat man. ;-)

That link was very interesting reading. I am going out now to recheck everything including that "load" signal. Will post results of all my
(re)testing.
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David Hunter

Could there be a problem with the throttle sensor? I know that sensor's data is exchange between the ecu's. I don't know if the rpm signal is also. When I get home tonight, I'll look into the manuals I have and see what other sensors play a roll in the transmission ecu.

DanR '94 964 343,000 miles (109,000 on the new engine)
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DanR

Dan: I really appreciate your thoughts. Since my original post i have swapped the TPS and even the Transmission control module. See my reply to Walt.

If you any ideas I'me all ears.
regards

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David Hunter

try here as well

http://www.swedishbricks.com/700900FAQ/Transmission-Auto1.html#960%20With%20AW-30/40%20Has%20Busy%20Shift:%20Electrical%20Glitches

if this was a 940 or 240 i would say your kickdown cable is mal adjusted.
should the 960 transmission also have this cable (usually attached to the throttle) this is where i would start looking.

kickdown cables out of adjustment will cause late, early and no upshifts

http://www.swedishbricks.com/700900FAQ/Transmission-Auto1.html#AT_Wont_Upshift

Thank you for your reponse. The AW 30 used in 960 and s90 does not have a kick down cable. It is totally controlled by electronics.

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David Hunter