GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 2003 🢒 Alero 🢒 Engine 🢒 Engine Controls - 2.2L (L61) 🢒 DTC P0502

Object Number: 794758 Size: SF
Master Electrical Component List
Manual Transmission Schematics
OBD II Symbol Description 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 on the transaxle and produces a pulsing voltage whenever vehicle speed is over 5 km/h (3 mph). The AC voltage amplitude and frequency increases with vehicle speed. The PCM converts the pulsing voltage into km/h (mph). The PCM supplies the necessary signal to the instrument panel for speedometer, odometer operation and to the cruise control and multi-function alarm module.

Conditions for Running the DTC
    • Engine speed is 1,700-3,600 RPM.
    • Throttle position is 0-1 percent.
    • Engine vacuum is 70-80 kPa (10-12 psi).
    • The above conditions are met for 5 seconds.

Conditions for Setting the DTC

Vehicle speed is less than 3 km/h (2 mph).

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.
    • The PCM disables Cruise Control.
    • The PCM commands the coolant fan ON.
    • 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 P0502 in PCM history.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic 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.

  1. This step ensures that the technician performed a Diagnostic System Check - Manual Transmission.

    2.

  2. This step tests to see if the PCM is receiving a signal from the VSS using the scan tool.

    3.

  3. This step tests the entire VSS system for proper output voltage.

    4.

  4. This step tests the VSS High Signal and VSS Low Signal circuits for opens, shorts and high resistance.

    5.

  5. This step ensures the technician inspects the VSS related mechanical components and mounting.

    6.

  6. This step verifies if the PCM has taken required action after setting DTC P0502.

    7.

  7. This step tests the VSS High Signal and VSS Low Signal circuits for total circuit resistance. 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.

    8.

  8. This step replaces the PCM. 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 CKP System Variation Learn Procedure in Engine Controls.

  9. This step validates that the repair has fixed the DTC under normal operating conditions.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check - Manual Transmission?

--

Go to Step 2

Go to Diagnostic System Check - Manual Transmission

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. Raise the vehicle and support the front control arms with jack stands.
  2. Start the vehicle.
  3. Engage the transmission in second gear.
  4. Observe the VSS data on the scan tool data list.

Is the vehicle speed greater than the specified value?

0 km/h (0 mph)

Go to Step 3

Go to Step 4

3

  1. Start the engine and put the transmission into NEUTRAL.
  2. Shift the transmission into various gears and accelerate and decelerate.
  3. Observe the speedometer on the instrument panel.

Is the speedometer operating normally?

--

Go to Step 12

Go to Step 4

4

  1. Turn the ignition switch OFF.
  2. Remove the VSS High Signal and VSS Low Signal circuit wires from the PCM connector.
  3. Connect the PCM connector to the PCM.
  4. Start the vehicle.
  5. Engage the transmission in second gear.
  6. With a DMM, measure AC voltage at the two VSS wires.

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

0.5 V AC

Go to Step 5

Go to Step 6

5

  1. Put the transmission in REVERSE and turn the ignition switch OFF.
  2. With a DMM, measure the total circuit resistance through both VSS circuits.

Is the total resistance within the specified value?

977-2,354 ohms

Go to Step 11

Go to Step 6

6

  1. Put the transmission in REVERSE and set the parking brake.
  2. Turn the ignition switch OFF.
  3. Install the VSS High and VSS Low circuit wires at the PCM.
  4. Disconnect the VSS and the PCM connectors.
  5. Test both the VSS High and VSS Low circuits for high resistance, opens, shorts to ground and shorts to each other.

Did you find any of the above conditions?

--

Go to Step 8

Go to Step 7

7

  1. Connect the PCM connector.
  2. Remove the VSS, but do not replace it at this time. Refer to Vehicle Speed Sensor Replacement .
  3. Inspect the VSS and the VSS rotor for the following conditions:
    4. • VSS damage
    • VSS rotor damage

Did you find any damage?

--

Go to Step 9

Go to Step 10

8

Repair the affected VSS High signal or VSS Low signal circuit, as necessary.

Did you complete the repair?

--

Go to Step 12

--

9

Replace the VSS rotor or make any necessary repairs to the VSS mount.

Did you complete the repairs?

--

Go to Step 12

--

10

Replace the VSS. Refer to Vehicle Speed Sensor Replacement .

Did you complete the repairs?

--

Go to Step 12

--

11

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 2.2L (L61).

Did you complete the repairs?

--

Go to Step 12

--

12

  1. Using the scan tool, clear the DTCs.
  2. Start the engine.
  3. Test drive the vehicle.
  4. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

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

--

System OK

Go to Step 2