GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1997 🢒 Sunfire 🢒 DTC 🢒 DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input

Object Number: 62500 Size: SF

Circuit Description

Vehicle speed is provided to the Powertrain Control Module (PCM) by the Vehicle Speed Sensor Assembly (VSS Assy.), which is a Permanent Magnet (PM) generator mounted to the transmission case. The PM generator produces an AC voltage as the transmission's speed sensor rotor teeth pass in front of the sensor's magnet. The AC voltage level increases as the speed of the vehicle increases. The PCM converts the AC voltage into a digital signal. The PCM uses the signal to calculate the vehicle speed, and when to apply the Torque Converter Clutch (TCC).

When the PCM detects a low vehicle speed and there is a high engine speed in a drive range, then DTC P0502 sets. DTC P0502 is a type A DTC.

Conditions for Setting the DTC
    • No MAP DTCs P0107 or P0108
    • No TP DTCs P0122 or P0123
    • No Vehicle Speed Sensor (VSS) Assy. DTC P0503.
    • The transmission is in a drive range.
    • The TP angle is greater than 12%.
    • MAP is greater than 50 kPa.
    • The engine speed is 2500-4775 RPM.
    • The vehicle speed is less than 3.2 km/h (2 mph).
    • All of the above conditions are met for four seconds.

Action Taken When the DTC Sets

The PCM illuminates the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL after three consecutive ignition cycles without a failure reported.
    • A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.

Diagnostic Aids
    • Inspect for Electromagnetic Interferences (EMI) induced on circuit 400 and circuit 401 by an improperly routed harness.
    • Brake Torquing the vehicle could set a DTC P0502.
    • Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring for poor electrical connections at the VSS Assy. Look for the following conditions:
       - A bent terminal
       - A backed out terminal
       - A damaged terminal
       - Poor terminal tension
       - A chafed wire
       - A broken wire inside the insulation
    • When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.

Test Description

The numbers below refer to the Step numbers on the diagnostic table.

  1. This Step tests for a vehicle speed signal.

    2.

  2. This Step checks for the VSS Assy. ability to produce an AC voltage.

    3.

  3. This Step checks for correct circuit resistance.

    4.

  4. When the VSS Assy. is disconnected, the circuit resistance should be infinite.

    5.

  5. This Step checks for improper voltage in the circuit.

    6.

  6. This Step inspects for possible mechanical problems.

    7.

  7. Replace the PCM only after you have completed the preceding diagnostic steps.

DTC P0502

Step

Action

Value(s)

Yes

No

1

Were you sent here from the "Powertrain On-Board Diagnostic (OBD) System Check"?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Install the Tech 2 Scan Tool Diagnostics .
  2. With the engine OFF, turn the ignition switch to the RUN position.

    3. Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

  3. Record the DTC Freeze Frame and Failure Records.

    4. Notice: Support the lower control arms in the normal horizontal position in order to avoid damage to the drive axles. Do not operate the vehicle in gear with the wheels hanging down at full travel.

  4. Raise and support the drive wheels.
  5. Start and idle the engine.
  6. Place the transmission in Drive.

With the drive wheels rotating, does the transmission output speed increase when the wheel speed increases?

--

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the C1 (Blue) and the C2 (Black) PCM connectors.
  3. Using the J 35616-A Connector Test Adapter Kit, connect the ohmmeter between PCM terminals C1-64 and C2-61.
  4. Select AC volts.
  5. Turn the ignition switch to the RUN position.
  6. Rotate the front drive wheel by hand.
  7. Observe the voltmeter display.

Can a voltage value greater than the specified amount be obtained?

0.5v A/C

Go to Step 17

Go to Step 4

4

Select ohms on the DVOM in order to measure circuit resistance.

Is the circuit resistance within the specified range?

139-376ohms

Go to Step 9

Go to Step 5

5

Is the circuit resistance greater than the specified value?

376 ohms

Go to Step 12

Go to Step 6

6

Is the circuit resistance less than the specified value?

139 ohms

Go to Step 7

--

7
  1. Leave the DVOM test leads connected.
  2. Disconnect the VSS Assy. connector at the transmission.

Is the circuit resistance less than specified?

139 ohms

Go to Step 8

Go to Step 16

8

Inspect circuits 400 and 401 for being shorted together.

Refer to Troubleshooting Procedures, Section 8.

Did you find the condition?

--

Go to Step 13

--

9

Inspect circuit 400 for a short to ground.

Refer to Troubleshooting Procedures, Section 8.

Did you find the condition?

--

Go to Step 14

Go to Step 10

10
  1. Reconnect the C1 and C2 PCM connectors.
  2. Select AC volts.
  3. Select DC volts.
  4. Using the J 35616-A Connector Test Adapter Kit, connect the voltmeter test leads to terminals A and B of the VSS Assy. connector end.
  5. Turn the ignition to the RUN position.

Does the voltmeter display system voltage?

--

Go to Step 11

Go to Step 15

11

Inspect circuit 400 for a short to power.

Refer to Troubleshooting Procedures, Section 8.

Did you find the condition?

--

Go to Step 14

--

12

Inspect circuits 400 and 401 for an open.

Refer to Troubleshooting Procedures, Section 8.

Did you find the condition?

--

Go to Step 13

Go to Step 16

13

Repair circuits 400 and 401.

Refer to Electrical Repair.

Is the repair complete?

--

Go to Step 18

--

14

Repair circuits 400.

Refer to Electrical Repair, Section 8.

Is the repair complete?

--

Go to Step 18

--

15
  1. Remove the VSS Assy.refer to VSS Assy. Replacement in On-Vehicle Service.
  2. Inspect the VSS Assy. and the transmission for the following:
    3. • Incorrect VSS Assy.
    • VSS Assy. damage
    • Excessive VSS Assy. to Speed Sensor Rotor gap
    • Incorrect Speed Sensor Rotor alignment
    • Speed Sensor Rotor damage

Refer to Unit Repair.

Is the repair or replacement complete?

--

Go to Step 18

--

16

Replace the VSS Assy.

Refer to VSS Assy. Replacement in On-Vehicle Service.

Is the replacement complete?

--

Go to Step 18

--

17

Replace the PCM.

Refer to PCM Replacement, Section 6.

Is the replacement complete?

--

Go to Step 18

--

18

In order to verify your repair, perform the following procedure:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle at a speed greater than 3 km/h (2 mph) for 4 seconds.
  4. Select Specific DTC. Enter DTC P0502.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1