DD#1 drives a 5 spd manual 2008 Hyundai Accent. Her CEL is on and she needs to pass emissions in order to renew her plate sticker. The code is P0501 VSS failure. When I do live data, on my scanner, it shows 0 mph regardless of actual speed. The speedometer reads properly. There is a VSS on the transaxle and a wheel speed sensor on the front right hub. My question is which sensor am I reading with my scanner and which one is sending info to the speedometer? I hate throwing parts at a problem so I'd like to pinpoint which sensor does what or if there can be another cause I'm overlooking.
In reply to Wayslow:
There is a GRM way to test ABS sensors that may also work on the one in the gearbox. Use a digital multimeter on the AC scale, connect the leads to the pins on the sensor plug and spun the wheel. If there is voltage that fluctuates with wheel speed the sensor is probably good. No voltage or a signal at near constant voltage is bad. If it show voltage before you spin the wheel it's probably bad. I don't know how they can have voltage before the wheel spins, but I've seen that a couple times.
IIRC, the computer uses the "ABS" sensor.
Why they can't share that data across CAN from/to the instrument cluster, I got no clue.
It may be coming from the cluster - I know some Miatas are like that. Info goes to the cluster, then to the ECU. So you can have a functioning speedo with no VSS in the ECU.
You need a wiring diagram.
In reply to Keith Tanner:
I have a regular maintenance manual but it doesn't have a detailed wiring diagram for engine management stuff. i haven't had any luck finding anything reliable on line either. This is why I come here.
Unplug one or the other and see if the speedo dies.
NEALSMO
UltraDork
1/31/17 3:59 p.m.
Internet wisdom (subscription knowledge base) says r/f speed sensor is culprit
Keith Tanner wrote:
It may be coming from the cluster - I know some Miatas are like that. Info goes to the cluster, then to the ECU. So you can have a functioning speedo with no VSS in the ECU.
You need a wiring diagram.
Kia/Hyundai are weird sometimes. On a non-ABS car, they will still have a tone ring and wheel speed sensor on the right front for the computer.
I remember more vividly now. A trans shop we work with got their butt kicked by a car (Elantra?) with a persistent VSS fault, they replaced the one that logic said was the VSS and we checked the wiring diagram for them since at the time our shop manuals were better than theirs. Trans VSS goes to the speedo, wheel speed sensor goes to computer.
I wonder now if they even HAVE the instrument cluster on CAN, or if they are doing stupid things like separate coolant temp/fuel level/etc senders for the cluster and for the computer. This is the same company that doesn't error check sensors against 5vref/groundref so who knows.
NEALSMO wrote:
Internet wisdom (subscription knowledge base) says r/f speed sensor is culprit
"i Ain't Tested Nothin'"? 
Knurled wrote:
Keith Tanner wrote:
It may be coming from the cluster - I know some Miatas are like that. Info goes to the cluster, then to the ECU. So you can have a functioning speedo with no VSS in the ECU.
You need a wiring diagram.
Kia/Hyundai are *weird* sometimes. On a non-ABS car, they will still have a tone ring and wheel speed sensor on the right front for the computer.
I remember more vividly now. A trans shop we work with got their butt kicked by a car (Elantra?) with a persistent VSS fault, they replaced the one that logic said was the VSS and we checked the wiring diagram for them since at the time our shop manuals were better than theirs. Trans VSS goes to the speedo, wheel speed sensor goes to computer.
I wonder now if they even HAVE the instrument cluster on CAN, or if they are doing stupid things like separate coolant temp/fuel level/etc senders for the cluster and for the computer. This is the same company that doesn't error check sensors against 5vref/groundref so who knows.
A 1.6 Miata has one coolant temp sensor for the ECU, one for the gauge and a thermoswitch for the fan. In 1994, they got rid of the thermoswitch. In 1999, they only had one sensor in the back of the head - but electrically it was two separate sensors combined in the same body. Sheesh.
