Canada - ABS/TCS - VSS and R/F Wheel Speed Sensor Diagnosis
GROUPENGINE ELECTRICAL
N0.
01-36-001
DATE
MARCH 16/01
MODEL
ALL
SUBJECT
VEHICLE SPEED SENSOR (VSS) AND RIGHT FRONT WHEEL SPEED SENSOR (RF-WSS) DIAGNOSIS
This bulletin is issued to explain:
^ the function of the Vehicle Speed Sensor (VSS) and the Right Front Wheel Speed Sensor (RF-WSS) on current Hyundai models
^ how they relate to Diagnostic Trouble Codes (DTCs),
^ to help diagnose conditions related to these sensors.
The table on page 6 can be used to determine which sensor is pertinent to which model when diagnosing a Vehicle Speed Sensor DTC.
Special Note:
DTC P0500 (VSS Fault) can be set by either the VSS or the RF-WSS depending on the model.
Vehicle Speed Sensor (VSS)
A Vehicle Speed Sensor in current Hyundai models can be one of two types:
1. An electrical sensor (either magnetic or a Hall Effect sensor) mounted directly on the transaxle. This type of sensor is driven by a gear on the transaxles final drive assembly. All current model vehicles use this type of sensor except for the Accent.
2. An electrical sensor (reed switch type) mounted to the speedometer head.
This type of sensor is driven by magnets mounted on the speedometer shaft, which is driven by the speedometer cable.
The primary functions of the VSS are to:
1. Send a signal to the speedometer for the vehicle's speed reading.
2. Send a signal to the ECM/TCM for engine management.
Right Front Wheel Speed Sensor (RF-WSS)
Some Hyundai vehicles have been using a sensor at the right front wheel since 1999 MY. This sensor is the same as a sensor for ABS, whether the vehicle is equipped with ABS or not. It reads a tone-wheel mounted on the right front axle, operating like a Crankshaft Position Sensor, does, and sends the signal to the ECM.
When driving over a very rough road, the engine can experience a drastic varying load, transferred from the wheels to the crankshaft, which may incorrectly appear to be an engine misfire to the ECM (as read by the Crankshaft Position Sensor).
This happens when a wheel begins to descend down into a pothole (speeding up the wheel), then ascend up as it exits the pothole (slowing down the wheel). This varying load is sensed at the crankshaft, which mimics a misfire, and under normal circumstances, would be thought to be a misfire. But, the RF-WSS is used, for this reason, to minimize the ECM's diagnosis when the sensor indicates that it is on a rough road (based on the "roughness" of the sensor's signal). At this time, misfire detection is suspended until the driving conditions have improved.
Vehicles with ABS/TCS
On vehicles equipped with ABS or ABS/TCS, the RF-WSS sends the signal to the ABSCM. If the vehicle uses the RF-WSS to determine a rough road condition (such as the 2001 Elantra XD), the ABSCM relays the signal to the ECM for use in determining rough road conditions.
The RF-WSS and tone-wheel on the right front axle are the same components on ABS and non-ABS equipped vehicles.
A malfunction of the RF-WSS may result in:
1. The ABS warning lamp illuminates.
2. DTC C1203 ("RF-WSS Open or Short") will be stored in the ABSCM memory.
Note:
All XG300's in Canada are equipped with ABS and TCS.
All current Hyundai vehicles are equipped with a VSS. However, not all are equipped with a RF-WSS. Vehicles that are not equipped with a RF-WSS use another means to determine rough road conditions for misfire monitoring. For example, the Tiburon uses an Acceleration Sensor mounted on the front driverside shock tower.
The table shows the VSS application on the latest Hyundai models.
Diagnosis of the VSS and RF-WSS
There are four main symptoms of a VSS or a RF-WSS related fault:
1. The Check Engine Light is ON and a DTC related to the VSS or RF-WSS is stored in the ECM, TCM, or ABSCM.
2. The speedometer is inoperative
3. The Vehicle Speed data in the Hi-Scan Pro displays 0 kmh while the vehicle is moving. (Note: This symptom requires further investigation. The problem may also be the Hi-Scan Pro software.)
4. The Vehicle Speed data in the Hi-Scan Pro displays a high reading that is undeniably incorrect. In cases such as this, there may be speed limiter fuel cut-out because the ECM thinks the vehicle has reached its maximum vehicle speed, This may only happen at certain speeds.
Diagnostic Trouble Codes (DTC)
If a vehicle has a VSS related DTC, use the chart to determine which sensor or circuit may be at fault.
DTCs related to either the VSS or the RF-WSS will set a P0500 or a P0501 (on vehicles without ABS/TCS). The code description on the Hi-Scan Pro reads "Vehicle Speed Sensor - Abnormal", and does not indicate either the VSS or the RF-WSS, even if the RF-WSS, or its circuitry may have caused the DTC.
Example
A 2.4L Sonata has DTC P0500 ("Vehicle Speed Sensor") stored in the ECM's memory. This indicates a condition with the VSS mounted on the transaxle or its related circuitry. Whereas a 2.5L Sonata, DTC P0500 indicates a condition with the RF-WSS mounted on the right front hub, or its related circuitry.
Thus, for the Sonata DTC P0500 on different engine management systems (the 2.4's Melco versus the 2.5's Siemens) relates to a different sensor.
Recommendations
^ The DTC alone, does not indicate exactly which sensor or circuit may be related to the code. Refer to the chart when working with a VSS related code.
^ In most cases, the condition can be verified by checking the operation of the speedometer and/or the vehicle speed readout on the H-Scan Pro.
^ Once the correct sensor or circuit has been determined, diagnose the condition by checking the integrity of the circuit and the function of the sensor.
Diagnostic Procedure Example
1. The Check Engine Light is ON in a 2001 MY Elantra XD.
2. The DTC P0501 ("Vehicle Speed Sensor") is stored in the ECM's memory (P0501).
3. The chart on the next page, indicates that the RF-WSS is related to the DTC P0501.
4. Diagnose the sensor and the sensor's circuit.
^ Check that the sensor in operating properly (refer to the Shop Manual for specifications).
^ Check that the tone-wheel is not damaged, or that there may be some debris between the sensor and the tone-wheel, which would give an incorrect reading.