Speed sensor A - (error code P0500)

alandviv · Post by **alandviv** » 10 Nov 2008, 17:20

Hi All,
Hope someone can help. I have a 1998 V70 Automatic SW. This is a recurring problem. I get error code P0500 (speed sensor A) Does anyone know it's location? and is it hard to get to? The blinking arrow is on and so is the check engine light. The "w" is blinking on the console by the gear shifter, the "S" nor the "E" will change it. It seems to be stuck in a low gear. Oh, and did i mention this car is a tire eater!!! I've had both a front and rear alignment. It's such a nice looking car and does drive very nicely, but i'm getting very frustrated. UGH!!! Any advice you can give me will be so appreciated. Thanks.

alandviv · Post by **alandviv** » 10 Nov 2008, 17:21

sorry, it has 115K on it and it's a US car.

Post by **Ozark Lee** » 10 Nov 2008, 18:44

Is your ABS or TRACs light on?

That code often results from a bad ABS module and you will soon lose your speedometer as well if you don't deal with the ABS module. You may also have a PNP switch problem but the VSS signal from the ABS module also feeds the transmission control module and the lack of the signal can throw the transmission into limp mode.

...Lee

larryh · Post by **larryh** » 10 Nov 2008, 19:06

I don't think you have a speed sensor problem...from what I understand, the abs module goes out on every one of these cars (did on both of mine). the good news is, it's easy and pretty cheap to get it fixed, unless you have a shop do it.
This guy makes it easy, and i think there are others as well.
http://home.earthlink.net/~vicrocha/

alandviv · Post by **alandviv** » 10 Nov 2008, 21:09

No, my ABS light is not on.

Post by **Ozark Lee** » 10 Nov 2008, 21:20

Do the ABS and Tracs lights turn on when you turn the key to position II before you start the car? Some unscrupulous sellers simply remove the lamps and in the most honest scenario the lamps simply burned out.

At this age on the cars very few of us are original owners which prompts the question. We have no idea what the previous owner(s) did.

...Lee

alandviv · Post by **alandviv** » 21 Nov 2008, 12:47

My car has been at my brother-in-laws and I haven't been able to check if the ABS light actually works. I asked him today and he says it works when the key is on position II.

C@lvin · Post by **C@lvin** » 21 Nov 2008, 14:36

Speed sensors can malfunction, but it seems as though the ABS module failure is MUCH more frequent (I've had Victor Rocha rebuild two over the years).

The wheel sensors are located inboard of each wheel. They pick up magnetic pulses from a "cogged" pulse wheel integrated into the axle/hub assembly which sends a current to the ABS module in order to measure the wheel speed. Sometimes, the pulse wheel or the sensor itself can get "dirty" with metal particles which interferes with the propper signal. Also the sensor must remain at a specified gap from the pulse wheel in order to generate the electical pulse over the wire that connects the sensor to the ABS control module. Lastly the wire must not be broken or shorted.

I would suggest you make sure the sensors and pulse wheels are clean, the sensors are securely attached, and the wires are not cut or shorted. I don't remember where I got the specs for the resistance of each wheel sensor circuit, but that is another thing to check.

After I had Victor rebuild my V70 ABS module, the ABS continued to fail with the speed sensor error. I checked all the sensors and cleaned them and measured the impedence over the wires between the module and the sensor to no avail. Eventually I discovered that one front wheel was missing the axle nut (I have not idea for how long or where or when it was lost). This allowed just enough play in the hub/axle to take the sensor/pulse wheel gap out of spec. When I put a new nut on the axle, the problem disappeared.

These can be tricky things to troubleshoot. Luckily, it seems the majority of the time, it is the module and not the sensors. Good luck!

alandviv · Post by **alandviv** » 21 Nov 2008, 15:15

We're thinking it's the sensors. Especially since there is no ABS or TRACS light on. Thanks for your insight Calvin. Very informative, I'll pass this on to my brother-in-law.

Post by **BEJinFbk** » 21 Nov 2008, 15:40

C@lvin wrote:Speed sensors can malfunction, but it seems as though the ABS module failure is MUCH more frequent (I've had Victor Rocha rebuild two over the years).

The wheel sensors are located inboard of each wheel. They pick up magnetic pulses from a "cogged" pulse wheel integrated into the axle/hub assembly which sends a current to the ABS module in order to measure the wheel speed. Sometimes, the pulse wheel or the sensor itself can get "dirty" with metal particles which interferes with the propper signal. Also the sensor must remain at a specified gap from the pulse wheel in order to generate the electical pulse over the wire that connects the sensor to the ABS control module. Lastly the wire must not be broken or shorted.

I would suggest you make sure the sensors and pulse wheels are clean, the sensors are securely attached, and the wires are not cut or shorted. I don't remember where I got the specs for the resistance of each wheel sensor circuit, but that is another thing to check.

After I had Victor rebuild my V70 ABS module, the ABS continued to fail with the speed sensor error. I checked all the sensors and cleaned them and measured the impedence over the wires between the module and the sensor to no avail. Eventually I discovered that one front wheel was missing the axle nut (I have not idea for how long or where or when it was lost). This allowed just enough play in the hub/axle to take the sensor/pulse wheel gap out of spec. When I put a new nut on the axle, the problem disappeared.

These can be tricky things to troubleshoot. Luckily, it seems the majority of the time, it is the module and not the sensors. Good luck!

Great explanation of these sensors.
Someone should sticky this!