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Makes 🢒 Buick 🢒 1998 🢒 Skylark 🢒 DTC 🢒 DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input

DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input Manual Trans Only


Object Number: 50804 Size: SF
Engine Controls Components
VSS and Cruise Control
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

Circuit Description

Vehicle speed information is provided to the Powertrain Control Module (PCM) by the vehicle speed sensor (VSS). The VSS is a permanent magnet generator that is mounted in the transaxle and produces a pulsing voltage whenever vehicle speed is over about 3 mph (5 km/h). The AC voltage level and the number of pulses increases with vehicle speed. The PCM converts the pulsing voltage into km/h (mph) and then supplies the necessary signal to the instrument panel for speedometer, odometer operation and to the cruise control module and multi-function alarm module operation.

Conditions for Setting the DTC
    • Vehicle speed is less than 2 mph (3 km/h).
    • Engine speed is between 1700 and 3600 RPM.
    • Throttle Position (TP) is between 0-1%.
    • Engine vacuum is between 80-70 kPa.
    • Above conditions met for 5 seconds.
    • DTCs P0107, P0108, P0122, and P0123 not set.

Action Taken When the DTC Sets
    • The malfunction indicator lamp (MIL) illuminates.
    • The PCM records the operating conditions at the time when the diagnostic fails. This information stores in the Freeze Frame and Failure Records buffers.
    • A history DTC stores.
    • The coolant fan turns ON.

Conditions for Clearing the MIL/DTC
    • The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.
    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • The MIL/DTCs can be cleared by using the scan tool.

Diagnostic Aids
    • An Intermittent problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation.
    • VSS high and low CKT(s) should be thoroughly checked for the following conditions:
       - Backed out terminals
       - Improper mating
       - Broken locks
       - Improperly formed
       - Damaged terminals
       - Poor terminal to wiring connections
       - Physical damage to the wiring harness or for proper routing
    • Ensure the VSS is correctly torqued to the transmission housing.
    • Refer to Symptoms .

Test Description

Numbers below refer to the step numbers on the Diagnostic Table.

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.

    2.

  2. The permanent magnet generator only produces a signal if the drive wheels are turning greater than 3 mph (5 km/h). This step determines if DTC P0502 is the result of a hard malfunction or an intermittent condition.

    3.

  3. Proper engine loads cannot be achieved in a shop environment to properly run the vehicle within the Freeze Frame Data conditions. It will be necessary to drive the vehicle on the road to obtain the proper engine loads.

    4.

  4. This step verifies that the PCM is receiving a signal from the vehicle speed sensor.

    5.

  5. Refer to service bulletin information for the latest calibration update.

    6.

  6. Refer to the latest Techline information for programming procedures.

    7.

  7. A resistance reading that is higher than the specified value indicates that the VSS circuitry is open.

    8.

  8. If the displayed resistance were less than the 1,300 ohms, the VSS high and low circuits are shorted together. If the resistance value within the specified value, check the VSS high and low circuits for a short to ground.

    9.

  9. This checks the resistance of the VSS if no opens or shorts were found on the VSS high and low circuits.

    10.

  10. The replacement PCM must be programmed and the crankshaft position system variation procedure must be preformed. Refer to the latest Techline procedures for PCM reprogramming and Crankshaft Position System Variation Learn .

DTC P0502-Vehicle Speed Sensor (VSS) Circuit Low Input (Manual Trans.)

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to

Powertrain On Board Diagnostic (OBD) System Check

2.4L

or

Powertrain On Board Diagnostic (OBD) System Check 2.2L

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.

  1. Turn ON the ignition switch leaving the engine OFF.
  2. Install a scan tool.
  3. Raise the drive wheels.
  4. Support the lower control arms so that the drive axles are in a horizontal (straight) position.
  5. Start the engine.
  6. Allow the engine to idle in gear.

Does the scan tool display vehicle speed above the specified value?

0 MPH

Go to Step 3

Go to Step 4

3

  1. Turn ON the ignition switch leaving the engine OFF.
  2. Review the Freeze Frame data and note the parameters.
  3. Start the engine.
  4. Operate the vehicle within the Freeze Frame conditions and Conditions For Setting The DTC as noted.

Does the scan tool display the vehicle speed above the specified value?

0 MPH

Go to Step 14

Go to Step 4

4

  1. Turn the ignition switch OFF.
  2. Disconnect the PCM electrical connectors.
  3. Connect a DMM between the terminals of the following circuits:
    4. • VSS high
    • VSS low
  4. Measure the AC voltage with the DMM while rotating the drive wheels by hand.

Is the AC voltage greater than or equal to the specified value?

0.5V

Go to Step 5

Go to Step 7

5

Check for the most current calibration ID number.

Is the latest calibration ID in the vehicle?

--

Go to Step 13

Go to Step 6

6

Update the PCM with the latest calibration ID.

Is the action complete?

--

Go to Step 14

--

7

Measure the resistance with a DMM at the PCM electrical connector terminals between the following circuits:

    • VSS high
    • VSS low

Is the resistance greater than the specified value?

870ohms

Go to Step 8

Go to Step 9

8

  1. Check the VSS high circuit for an open.
  2. Repair the circuit as necessary.

Was a repair necessary?

--

Go to Step 14

Go to Step 11

9

Was the resistance value within or equal to the specified value?

530-870ohms

Go to Step 10

Go to Step 11

10

  1. Check the VSS high circuit for the following conditions:
    2. • Short to ground
    • VSS high and VSS low being shorted together
  2. Repair the circuit as necessary.

Was a repair necessary?

--

Go to Step 14

Go to Step 11

11

  1. Remove the VSS. Refer to Vehicle Speed Sensor in Manual Transmission.
  2. Connect a DMM between the VSS sensor terminals.
  3. Measure the resistance in the VSS sensor with the DMM.

Is the resistance value within the specified value?

530-870ohms

Go to Step 13

Go to Step 12

12

Replace the Vehicle Speed Sensor (VSS). Refer to Vehicle Speed Sensor in Manual Transmission.

Is the action complete?

--

Go to Step 14

--

13

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 14

--

14
  1. Using the scan tool, clear the DTCs.
  2. Start the engine.
  3. Idle at normal operating temperature.
  4. Operate the vehicle within the conditions for setting this diagnostic as specified in the supporting text.

Does the scan tool indicate that this diagnostic has ran and passed?

--

Go to Step 15

Go to Step 2

15

Check if any additional DTCs are set.

Are any DTCs displayed that have not been diagnosed?

--

Go to applicable DTC table

System OK