1998 S90 Transmission and Speedometer problem.

kbmusic · Post by **kbmusic** » 20 Aug 2012, 22:41

I have a 1998 Volvo S90, U.S. spec (2.9L L6, 4-speed automatic) with 201k miles. Almost every time I drive the vehicle, at some point the speedometer will stop working, the amber "Up" arrow on the dash and the "E" and "W" button lights by the gearshift will all flash, and the Check Engine light will illuminate. The ABS light does NOT illuminate. OBD II scanner reports code P0500 (Vehicle Speed Sensor fault). The transmission itself will do odd things when this happens, such as hanging in first gear too long, or slipping around between gears at higher speeds (it does not lock into 3rd gear, the so-called "limp home" mode I've read about). The transmission shifts perfectly when this problem is not occurring. I have done a lot of research on this (on Matthew’s Volvo Site and beyond) and have seen numerous suggested causes, primarily a bad PNP sensor, but also a bad TPS sensor or Speed Sensor. Some people have suggested that it is the Vehicle Speed Sensor mounted on the transmission, while others have said that the 1998 S90 does not have a Vehicle Speed Sensor on the transmission itself. Others have suggested that it is probably the speed sensor mounted on the differential, but that if this were the case the ABS light should come on as well. I am a fairly competent shadetree mechanic, and have a multimeter, but am not by any means an electrical troubleshooting wizard. I’m hoping to find out for sure which sensor is malfunctioning before I start taking things apart and buying expensive parts which I may not even need. The speed sensor on the differential is fairly easy to get to, but the stuff on the transmission (PNP sensor, etc.) requires removing part of the exhaust system, so I’d obviously like to avoid that if I can. One other thing: some threads suggested “rowing” the gearshift back and forth several times from “P” to “L” with the engine off to clean the contacts on the PNP sensor, and this actually has helped the problem, but it always comes back after I’ve driven the car for more than 15-20 minutes. So, I’m not sure if rowing the gearshift is actually doing anything or just a coincidence. I’m also worried about damaging the transmission by doing this every time I drive the car. If anyone has any insight on this problem I would greatly appreciate it!

Post by **jimmy57** » 20 Aug 2012, 23:15

The speedometer converts an analog AC voltage sine wave into a digital square wave for the transmission (cruise control and radio and ECM for that matter too).
My suspicion would be the connectors at the cluster followed by faulty speedo in the cluster.

kbmusic · Post by **kbmusic** » 21 Aug 2012, 15:14

Thank you for your reply. I took the car out again this morning for another test drive (I probably should have mentioned that I just purchased it 3 days ago), and based on the behavior I observed today, I think you're probably correct. The speedometer comes and goes - when it's working, the transmission works perfectly, cruise control works, etc. I'm relieved that it's probably not a mechanical problem or any number of sensors under the car, but it sounds like getting the dash panels off is a bit of a chore. I'll search around the forums to see if I can find a how-to that I can follow, if not I'll probably be back shortly. I have to mention that, despite its little problems, I think this 14 year old S90 might be the finest overall car I've ever owned. Moving into second place is the 1992 Eagle Premier ES Limited (basically an Americanized Renault 25) I owned from 2000-2006. I still regret letting go of that car . . .

Post by **precopster** » 21 Aug 2012, 16:35

The connectors on PNP and cluster are the first stop as with all intermittent faults.

The instrument cluster's circuit board has a couple off capacitors that can fail and this requires removal of the cluster to solder in some inexpensive components. It's been documented well over on Brickboard Forum with a picture tutorial but nothing here yet.

On my '92 960 which shares the same panel as your car I had the cluster off 4 years ago for speedo not working but couldn't source one of the capacitors. It recently failed again so it needs to come out another time.

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kbmusic · Post by **kbmusic** » 23 Aug 2012, 15:19

Thank you for the responses so far. Since my last post, I've done a lot more reading and a lot of poking around in the car. I read on one forum that a lot of the speedometer circuit board problems were corrected around '94, but I went ahead and pulled mine anyway. Everything looked okay (the board wasn't brittle and nothing looked burned, swollen, or unusual) and I made sure all of the connectors were secured tightly. I also cleaned the ground cable under the hood (31/53), and pulled the knee bolster out from the driver's side and checked the connector on the TCM to make sure it was still secured. I found nothing unusual and none of this seemed to help.

Then, I made one very strange discovery that may shed more light on this problem than anything else (please bear with me here):
During my research, I happened upon an eHow article discussing how to clear the check engine light on an S90. It said to turn the key to position I, press and hold the trip odometer reset button, turn the key to position 2, wait for the check engine light to flash four times, then on the fourth flash turn the key back to position I and release the button. Well, the check engine light never flashed (and I was never able to reset it); however, using this with the flashing "up" arrow (instead of the check engine light) allowed me to turn off the flashing arrow (and flashing buttons by the gearshift) and caused the speedometer to begin functioning again, albeit temporarily. Here's an exact step by step of what I've been doing:

1. Reset flashing transmission arrow light by following the above (four flash) procedure.
2. Start engine and begin driving - everything functions normally
3. After anywhere between 3-10 miles or so, and often after slowing to less than 10 mph or coming to a complete stop, the speedometer stops working and transmission lights begin flashing.
4. Pull over to the side of the road, turn off engine, perform flashing arrow reset procedure.
5. Start engine and begin driving - everything works again.
6. Repeat steps 3-5 ad infinitum.

I should note that if I simply shut the engine off and restart it (without doing the reset procedure) the trans warning lights still flash and the speedo doesn't work. Doing the reset procedure fixes it every time. I also no longer "row" the gearshift as I did before, so that isn't factoring into this at all.

What the heck is going on here?! Do you still think it's a problem with the PNP switch/connector, or with the speedometer circuit board? Could my TCM need to be reset (flashed)? Is this something I can do, or an independent electrical shop, or would I have to take it to a Volvo dealer? Could it be flaking out completely and needing replacement? Is anyone familiar with this whole "trip odometer reset/flashing light" procedure, or know exactly what it's doing to the car when I perform it?

Post by **precopster** » 23 Aug 2012, 16:14

I would still be heading toward the PNP itself. They wear and are a common service item. Symptoms of a PNP problem vary a lot depending on which contacts are worn. If you loosen the exhaust at the flange I believe you should get enough room to remove it. If not loosen all the manifold studs and move the manifold back on the studs without removing it totally. There are a lot of fandangled heat shields to remove so be patient.

Mechanical wear of a high failure rate component should always be investigated before replacing/reflashing engine computers.

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kbmusic · Post by **kbmusic** » 23 Aug 2012, 18:17

Thanks again precopster. I guess I'll plan on ordering a new PNP switch. One last question before I get started . . . is there any sense or hope in trying to examine and clean the switch and connectors when I get down there, or should I just get a new switch and replace it without any further experimenting? It looks like I can get a new switch for about $130-150 USD, which isn't too terrible, and I'd rather take care of it now than have to climb back under there in December (when it's below freezing outside) and replace it anyway. I've probably just answered my own question, but if you have any additional words of advice, I'd appreciate hearing them.

lummert · Post by **lummert** » 23 Aug 2012, 19:39

I was doing some reading and found a gear position switch mentioned. I looked up the part and found that it's part of the PNP switch.

I found a link that may match your car's symptoms:

http://www.volvoclub.org.uk/faq/Transmi ... placenment

I have access to a 92 960 (which uses the same PNP switch). I may be able to have the car lifted to remove the switch to check it out and ship it to you.

Post by **jimmy57** » 23 Aug 2012, 22:54

The issue with Gear Position Sensor/PNP is that it cannot kill the speedo like you are seeing but a speedo issue will definitely cause speedo to go away and transmission shifting issue and kill the cruise control also.
Not all failures of the speedometer are visible on the circuit boards.

Post by **precopster** » 24 Aug 2012, 00:59

In accordance with jimmy57 there with component failure. It may have been a great opportunity to solder in some new capacitors while you were there. Do you have the values and locations on the board of the suspect components?

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