Description

Vehicle Speed Signal Description

1. Fault Code:
Vehicle Speed Sensor Malfunction P0500

2. Monitoring Procedure

Summary
Problems with the road speed sensor will be detected using a number of tests. An engine load test will check for a sustained high engine load being present within a given range of engine speeds and a low road speed. A check is performed using the gearbox retard request signal from the electronic automatic gearbox. If these requests are being received with a low road speed then the test will fail.

Engine Load Test
If the engine load is above a constant, RS DIAG LOAD THRESHOLD for a time greater than RS DIAG LOAD TIME with the engine speed above RS DIAG ENGINE SPEED MIN and RS DIAG LOW ROAD SPEED is true then a fault counter (RS DIAG LOAD FAULTS) will be incremented. Should the test be passed then the fault counter will be decremented to until zero.
If the value of the fault counter reaches the limit value RS DIAG FAULT LIMIT then a road speed fault is present.

Gear Change Request Check
On electronic automatic vehicles a signal is sent from the gearbox ECM to request an ignition retard to smooth out gear changes.
This signal, GEAR CHANGE REQUEST, will be monitored and if it occurs when RS DIAG LOW ROAD SPEED is true then a fault count RS DIAG GEAR FAULTS will be incremented. On each ignition retard request when RS DIAG LOW ROAD SPEED is false and also on each transition of the neutral/drive switch state NDSWITCH OUTPUT the fault counter is decremented.
If the value of the fault counter reaches the limit value RS DIAG GEAR FAULT LIMIT then a gear change fault is present until the counter reaches zero.

3. Primary Detection Parameter
Road Speed - Road speed sensor edges indicating > 1 mph.
Presence of 30 gear change requests during low road speed conditions.

4. Fault Criteria Limits
Presence or not of road speed sensor edges.

5. Monitoring Conditions
The check for road speed will occur under conditions where engine load and speed suggest that the engine is working against genuine road loads (not ancillary loads).
RS DIAG LOAD THRESHOLD - 80% load
RS DIAG LOAD TIME, a time period ensuring that load is constant, 5 seconds.
RS DIAG ENGINE SPEED MIN, 2500 rpm
RS DIAG FAULT LIMIT 40 events
The check for a gear change request signal from the gearbox ECM is performed whenever there is a low road speed indicated from the road speed sensor.

6. Monitoring Time Length / Frequency of Checks
The road speed sensor diagnostic operates at a frequency of 10Hz.

7. Criteria for Storing Fault Code
Two successive trips where the road speed diagnostic indicates a failed road speed sensor.

8. Criteria for Illuminating MIL
Two successive trips where the road speed diagnostic indicates a failed road speed sensor.

9. Criteria for Determining Sensor Functionality
The road speed sensor produces a non-linear output; the criteria will be signal/no signal.