850 t5 Tyre size problem

tetleyteabag · Post by **tetleyteabag** » 28 May 2014, 06:17

I have bought a 1996 850 t5 auto estate which is currently fitted with 55 profile tyres on the rear and 50's on the front. Could this be the cause of the transmission light arrow flashing on the dash as well as the sport and economy lights doing similar on the centre console. Thanks.

Post by **tryingbe** » 28 May 2014, 07:00

Get the code read first.

Post by **precopster** » 28 May 2014, 07:00

It's not so much the profile that matters but the profile in relation to the width which provides circumference of the wheel.

The only wheel size that matters are the fronts. On an 850 the usual speedo error is the symptom....no codes or ABS issues.

What size exactly are you running and what size rims 15s or 16s?

The car needs to be read via the OBDII port. It will have a transmission code.

tetleyteabag · Post by **tetleyteabag** » 29 May 2014, 11:30

I'm running 205 55 16s on the rear and 205 50 16s on the front

tetleyteabag · Post by **tetleyteabag** » 29 May 2014, 12:27

As regards to the code, the reading shows P0500. I can reset it and the car performs as it should in sport mode but a short time after it reverts back to the flashing arrow and sport and economy lights flashing and drives in economy mode.

Post by **precopster** » 30 May 2014, 07:47

Vehicle speed sensor A located on gearbox (there are two of them) is not working correctly. Swap one for the other and see if the code changes. If it doesn't it will be a wiring to speed sensor problem.

Post by **Ozark Lee** » 30 May 2014, 13:58

Hmm - the '96 model should get VSS information from the ABS module which in turn derives its speed information from the wheel sensors. Mismatched tyre sizes could be confusing the ABS module since it is getting slightly different speed information from the fronts vs the rears.

Volvo originally shipped the turbos with 205/50/16 tyres but the rims kept getting bent up from potholes and they changed to 205/55/16 tyres. On the early cars that were actually shipped with the 50 series tyres they had a recall in the US and they replaced the wheels and gave the owner a voucher to buy a new set of tyres.

...Lee

Post by **precopster** » 30 May 2014, 15:38

Good call Ozark, though I ran 205/50/17s on front and 215/45/17s on the rear of my 2000 V70 and never had codes....a 6% difference.terrible ride though. The OP's difference is higher.

Does the '99/00 use the gearbox sensors for speed?

Post by **abscate** » 04 Jun 2014, 05:01

In the States at least, the 99 uses the wheel sensors ABS module to generate speed info. When your ABS unit goes out, you lose speedo info. I drove my car for 6 months with a rpm-speed conversion written on a business card.

Post by **precopster** » 04 Jun 2014, 07:16

When I had the wrong sensor in my '99 V70 gearbox (transmission was from an 850) it called up an ABS P0500 code a couple of years ago.
This means that the ABS module (which is shared in the USA for the non Tracs/STC V70/S70 models) receives some info via the transmission sensors.

The correct sensor swapped from the original transmission cancelled the ABS light. Same code as OP however I HAD SPEEDO.

Perhaps things are done differently for the US market however that wouldn't make economic sense to add complexity to the production line.

If the OP has speedo and is just dealing with a code the gearbox sensor would be a logical place to investigate.

Regardless of where the signal is derived front tire sizes will alter the speed reading. I'm just dubious as to whether the rears also come into play on a FWD model.