960 Transmission shift prob, blinking up arrow, code P0500

tnkenmcd · Post by **tnkenmcd** » 13 Feb 2010, 11:35

Just bought a used 1996 960 and it's started having a transmission shift problem. Sometimes when I drive, the transmission suddenly changes gears, usually downshifting, and seems to have a hard time staying in high gear (overdrive) with steady (slight) throttle.

I get blinking UP arrow on dash, the blinking W S E lights, and Check Engine light. The code reader at Autozone gives code P0500 Speed Sensor.

From what I can tell by searching the forums, the P0500 is many times treated as an ABS problem, but in my case, I don't have ABS light and my ABS works. Other threads seem to indicate P0500 is PNP switch on gear selector. But I don't have any problems getting the shifter out of Park and it seems to select lower gears (3 L) just fine.

I pulled the speed sensor out of the transmission (right side, with green/bl and wh/bl leads), and it seems physically OK and the multimeter reads some resistance across the leads.

Can anyone recommend next action? I think there are more detailed codes I could get from the dealer, but I'd like to save that cost. The VADIS manual seems to suggest chasing upstream wiring looking for open, shorts, etc.

Oh, and sometimes this problem goes away, and the blinking UP arrow and W S E go away, but the Check Engine light remains.

Post by **billofdurham** » 13 Feb 2010, 12:01

Welcome to Matthew's Volvo Site.

When this occurs do you lose the speedometer?

Usually this fault code relates to the transmission speed sensor located on the left side of the transmission housing. This sensor supplies the transmission control module (TCM) with an RPM signal. The TCM then compares the transmission RPM with the vehicle speed and calculates torque converter slippage.

Check the connector at the transmission speed sensor.

Bill.

tnkenmcd · Post by **tnkenmcd** » 13 Feb 2010, 12:33

Speedometer always works.

When you say left side, do you mean left from when 1) standing in front facing the vehicle? Or 2) from the driver's seat? I pulled the part from right side of transmission relative #2.

tnkenmcd · Post by **tnkenmcd** » 13 Feb 2010, 12:55

This is the diagram, shows #12 as speed sensor and #13 as temperature sensor. And there's a manual's picture for the speed sensor.

What's odd about this is I remember those 3 connectors and then the part in the picture, but it was all located on the opposite side of the transmission. This picture shows the speed sensor on the left side, but I recall it being on the right side. I do know I was working on the part with green and white lead.

I'm going to double-check my information with a quick look under the vehicle.

tnkenmcd · Post by **tnkenmcd** » 13 Feb 2010, 13:34

Nevermind the confusion, so yes my car is just like the above diagrams. I must have remembered it wrong.

Anyway, I did check that speed sensor, and it's disconnected resistance across the sensor. And the upstream connector looked OK.

The VADIS says P0500 maps to AT-232

I've got these troubleshooting steps. Does anyone know where terminal 31/53 is? I think I know the other test points.

Can someone suggest a better next step than chasing this wiring?

Post by **billofdurham** » 13 Feb 2010, 15:31

One picture:

960 earth point 31_53.pdf: (635.39 KiB) Downloaded 2168 times

Bill.

tnkenmcd · Post by **tnkenmcd** » 15 Feb 2010, 20:27

Well, I think I got the problem fix. Or it's just "gone away"

I removed the TCM and disconnected it's connector. Read the resistance down to the transmission speed sensor across 22 & 37. It read 600 Ohms just like a direct reading and within specs.

The next steps suggested checking the wiring between the instrument cluster and TCM, but I didn't want to pull the Cluster and didn't see any other way to get to those connectors. All the information seems to indicate it's real easy to break dash trim on the 960.

So I skipped to checking and cleaning ground connections. 31/67 is easy to find, it's under the seat and I checked the other ground under the opposite seat (not sure it's ground number). Both of those seemed in good shape, but I disconnected and put a brush and cleaner on them anyways.

And then I checked and cleaned 31/53 which I found thanks to Bill. This ground was pretty dirty and it's in a location that gets a lot of water and dirt. So I removed and cleaned this one also.

My blinking up arrow and W S E lights are gone and I drove for a couple of days without a problem. Just tonight, I got the Check Engine cleared and still have not seen this problem return.

I find it hard to believe this problem is solved. But it was happening very often before I did this "work." Maybe the ground cleaning fixed it, or jarring the TCM...

tnkenmcd · Post by **tnkenmcd** » 16 Feb 2010, 05:31

The flashing light is back! Joy joy...

tnkenmcd · Post by **tnkenmcd** » 02 Mar 2010, 06:01

The fix was to replace the Transmission Control Module (TCM). I found one in a self-service salvage yard for $23. I think retail is about $400.

So far the error has not returned after about a week of daily use. Before, when I would reset the code and Check Engine light, the error would return within a day, so I'm confident of the fix.

Post by **billofdurham** » 02 Mar 2010, 11:04

The fix was to replace the Transmission Control Module (TCM). I found one in a self-service salvage yard for $23. I think retail is about $400

A good find!!!

Thank you for the update.

Bill.