I need help! P0502 code

[05Bonnie&Clyde]

"Vehicle speed sensor A circuit low input" Is it a hard job? Should I take it to the dealer or should I try it myself? If you do recommend DIY then what parts do I need ? And where is it located? Thanks to anyone with any info!

[CMNTMXR57]

Oh boy, this one has a lot of circuit testing... Do you want to tackle this yourself? Or do you just want to know what the source of the problem is?

Basically why this one sets is because vehicle speed (as determined by the VSS) is low in comparison to engine rpm's.

As mentioned a lot of circuit testing, looking for shorts/damage to harnesses/plugs at the PCM, VSS, VSS brake switch, etc. You'll be measureing voltages at terminals on the PCM, as well as VSS resitance. You may even need to make sure you have whatever GM calls the most recent calibration.

Obviously if you have wiring harness/plug damage, that will need repair, but ultimately parts that could be suspect are the VSS itself, VSS brake switch, and in worst case scenario, PCM replacement.

[05Bonnie&Clyde]

Well then, dealer it is! Thanks for the help! I'm not smart enough to even attempt this kind of procedure

[CMNTMXR57]

So yea, they're going to fix either one or more of the following;

- Check for most up to date PCM calibration.

If that doesn't work;
- Circuit repair
- Replace VSS brake switch
- Replaced VSS
- Replace PCM

That's what it boils down to.

[CMNTMXR57]

Also, now that I think about it, did you have a P070x something code, related to the PRNDL? If so, sometimes this can errantly set 0502. If not, no biggie, just had that thought come up.

[05Bonnie&Clyde]

No, it was only one code

[CMNTMXR57]

Ok, if there were two, you'd have to address the 070x code first.

[05Bonnie&Clyde]

Thanks again, hope this is covered under my ext warranty

[CMNTMXR57]

Should be. You may have to pay a deductible.

[05Bonnie&Clyde]

That shouldn't be too bad.

[05Bonnie&Clyde]

-Update- the dealer said it just needs a speed sensor and it isn't covered under warranty )-; $170

[05Bonnie&Clyde]

Where is the speed sensor located at on this car?

[harofreak00]

Its on the differential end of the transmission.

Don't pay $170 for the sensor, they are only like $15 on RockAuto.com

[CMNTMXR57]

The speed sensor is the VSS (Vehicle Speed Sensor).

Yea, Rock Auto, or even a used one elsewhere.

[05Bonnie&Clyde]

Bought one, thanks! I'll put it on Saturday when I get off from work. Any tips on how to put it on easy?

[CMNTMXR57]

Wait, I thought you had an extended warranty? This should be covered and they should be doing it.

Anyway, you'll have to get under the car, back of the transmission, on the diff side (as mentioned), which faces the passenger side. You will see a stamped steel brace that connects betwen the transmission/transaxle and the engine (I think it bolted up to the cylinder head on the engine side).

Once this brace is removed, it should be the big sensor facing upwords on the snout. Remove the electrical pigtail, undo the retaining bolt, and twist/pull it out. Be careful not to lose the "O" ring seal that may be there.

It's all reverse to put it back in. I think the bolt to hold down the sensor itself is 89 in/lb (typical on these size/style bolts). The brace probably has a 30 - 35 lb/ft torque spec for the 3 bolts.

[05Bonnie&Clyde]

It's a third party warranty I got from the dealer I bought it from(a Cadillac dealer in Myrtle Beach S.C.) but appearently it isn't coverd by it. Thanks for all your help you save me a whole lot of grief !

[CMNTMXR57]

Sorry to hear, this is one of my rants when people ask what extended warranty they should get? Only get a manufacturer backed one. This is one example why.

Not to rub salt in the wound, but had this been GMPP, it would have been fixed, sans a small deductible on your behalf, you'd have your car back, and your Saturday would be free for other things. Not that playin' with your car is a bad thing, mind you...

[05Bonnie&Clyde]

Yeah, I wish I had a factory warranty. Oh well, at least I get to boost my "reśume" haha!

[CMNTMXR57]

It really won't be that bad. I think the key will be getting the car up high enough to where you can get to the back of that engine/trans area comfortably.