Circuit Description
The vehicle speed sensor (VSS) assembly provides vehicle speed information to the powertrain control module (PCM). The VSS assembly is a permanent magnet generator. The VSS produces alternating current (AC) as the rotor teeth on the output shaft of the transmission (2WD) or transfer case (4WD) pass through the magnetic field of the sensor. The frequency and amplitude of the AC waveform increase as vehicle speed increases.
If the PCM detects no vehicle speed for a specified length of time, while other sensors indicate that the vehicle is moving, DTC P0500 sets. DTC P0500 is a type B DTC.
Conditions for Running the DTC
| • | No manifold absolute pressure (MAP) sensor DTCs P0106, P0107 or P0108. |
| • | No throttle position (TP) or accelerator pedal position (APP) sensor DTCs P0121, P0122, P0123, P1120, P1125, P1220, P1221, P1514, P1515, P1516, P1517, or P1518. |
| • | No crankshaft position sensor DTCs P0335 or P0336. |
| • | The ECT is greater than 35°C (95°F). |
| • | The TP sensor angle is 5-100 percent. |
| • | The engine speed is greater than 1,000 RPM. |
| • | The MAP is 40-100 kPa (6-15 psi). |
| • | All of the above conditions are met for two seconds. |
Conditions for Setting the DTC
The PCM detects no vehicle speed for 50 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails. |
| • | Cruise Control is disabled. |
| • | The PCM records the operating conditions at the time when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records. |
| • | The PCM stores P0500 in PCM history. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL after three consecutive ignition cycles in which the diagnostic test runs and passes. |
| • | The PCM cancels the DTC default actions when the fault no longer exists and the DTC passes. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring. |
| • | A Scan Tool can clear the MIL/DTC. |
Diagnostic Aids
Ensure the VSS is correctly torqued to the transmission housing.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The resistance measurement will not change if either the VSS high signal circuit or the VSS low signal circuit, but not both, is shorted to ground. The vehicle speed detector in the PCM and the VSS are matched in such a way that an open or a short to ground in the VSS low signal circuit will not usually cause a loss of speed signal or a DTC P0500 to set. The lower resistance value given represents the nominal resistance specification of the VSS at -40°C (-40°F), minus the manufacturing tolerance specification of 10 percent. The higher resistance value given represents the nominal resistance specification of the VSS at 150°C (302°F), plus the manufacturing tolerance specification of 10 percent.
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This step isolates the short between the VSS and the wiring.
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Do not skip Step 7. The DMM will detect AC voltage if the VSS high signal circuit is shorted to ground.
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The replacement PCM must be programmed and the crankshaft position system variation procedure must be performed. Refer to the latest Techline procedures for PCM reprogramming and to Powertrain Control Module (PCM) Programming in Engine Controls.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Manual Transmission ? | -- | Go to Step 2 | |||||||||
2 |
Notice: In order to avoid damage to the drive axles, support the lower control arms in the normal horizontal position. Do not run the vehicle in gear with the wheels hanging down at full travel. Important: Record the Failure Records before clearing the DTCs. Using the Clear Info function erases the Failure Records from the PCM. Does the Scan Tool display vehicle speed above the specified value? | 0 mph | Go to Step 3 | Go to Step 4 | ||||||||
3 |
Does the Scan Tool display vehicle speed above the specified value? | 0 mph | Go to Intermittent Conditions (4.3 L) or Intermittent Conditions (4.8 L) in Engine Controls | Go to Step 4 | ||||||||
4 |
Did the PCM require a calibration update? | -- | Go to Step 14 | Go to Step 5 | ||||||||
Is the resistance within the specified range? | 966-2200 ohms | Go to Step 7 | Go to Step 6 | |||||||||
6 | Test the VSS high signal circuit and the VSS low signal circuit for the following conditions:
Refer to Circuit Testing in Wiring Systems. Did you find and correct a condition? | -- | Go to Step 14 | Go to Step 11 | ||||||||
7 | Measure the resistance between terminal C2 21 and ground. Is the resistance greater than the specified value? | 50 K ohms | Go to Step 10 | Go to Step 8 | ||||||||
Is the resistance greater than the specified value? | 50 K ohms | Go to Step 11 | Go to Step 9 | |||||||||
9 | Repair the short to ground in the VSS high signal circuit. Did you complete the repair? | -- | Go to Step 14 | -- | ||||||||
Is the AC voltage equal to or greater than the specified value? | 0.5 V | Go to Step 13 | Go to Step 11 | |||||||||
11 |
Did you find and correct a condition? | -- | Go to Step 14 | Go to Step 12 | ||||||||
12 | Replace the VSS. Refer to Vehicle Speed Sensor . Did you complete the repair? | -- | Go to Step 14 | -- | ||||||||
Replace the PCM. Refer to Powertrain Control Module Replacement (4.3 L) or Powertrain Control Module Replacement (4.8 L) in Engine Controls. Is the action complete? | -- | Go to Step 14 | -- | |||||||||
14 |
Does the Scan Tool indicate that this diagnostic has run and passed? | -- | System OK | Go to Step 2 |
