GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Cavalier 🢒 DTC 🢒 DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input

Object Number: 62392 Size: SF
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Automatic Transmission Output (Shaft) Speed Sensor (A/T OSS) provides vehicle speed information to the Powertrain Control Module (PCM). The A/T OSS is a Permanent Magnet (PM) generator mounted to the transmission case. The PM generator produces an AC voltage as the transmission speed sensor rotor teeth pass through the sensor's magnetic field. 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 vehicle speed signal to determine shift timing, Torque Converter Clutch (TCC) apply, TCC release, and gear ratio calculations.

When the PCM detects a low output speed and the vehicle has a large engine speed in a drive gear, then DTC P0502 sets. DTC P0502 is a type B DTC.

Conditions for Setting the DTC
    • No MAP DTCs P0107 or P0108
    • No TP DTCs P0121, P0122, or P0123
    • No A/T ISS DTCs P0716 or P0717.
    • No TFP Val. Position Sw. DTC P1810
    • The transmission is in a drive range.
    • The TP angle is greater than 15%.
    • The MAP is greater than 50 kPa.
    • The input speed is greater than 2000 RPM.
    • The output speed is less than 3.2 km/h (2 mph).
    • All of the above conditions are met for 2.5 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the Malfunction Indicator Lamp (MIL).
    • The PCM commands maximum line pressure.
    • The PCM freezes shift adapts from being updated.
    • The PCM calculates output speed from input speed, engine speed, and commanded gear.
    • DTC P0502 is stored in the PCM history.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL after three consecutive trips 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.
    • The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM.

Diagnostic Aids
    • The condition may be intermittent. Inspect for a loose A/T OSS, or poor sensor connection.
    • Inspect the wiring for poor electrical connections at the PCM and the A/T OSS 2-way connector 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
       - Moisture intrusion
       - Corrosion
    • When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.
    • Inspect for a damaged A/T OSS. Inspect for damaged transmission rotor teeth.
    • A slipping forward clutch could set DTC P0502.

Test Description

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

  1. This step tests for a signal from the A/T OSS.

    2.

  2. This step tests the ability of the A/T OSS to produce an AC voltage.

    3.

  3. This step measures for correct circuit resistance from the PCM connectors to the A/T OSS.

    4.

  4. When the A/T OSS is disconnected, circuit resistance should be infinite.

    5.

  5. This step tests for improper voltage in the circuit.

    6.

  6. This step inspects the A/T OSS and the A/T OSS rotor for mechanical failure.

    7.

  7. This step replaces the PCM after testing the component and circuitry.

DTC P0502 Output Speed Sensor Circuit -- Low Input

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 Scan Tool .
  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. Using the Clear Info function will erase the stored Freeze Frame and Failure Records from the PCM.

  3. Record the DTC Freeze Frame and Failure Records, then clear the DTCs.

    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 J 39200 Digital Multimeter (DMM) between PCM terminals C1-64 and C2-61.
  4. Select AC volts.
  5. Turn the ignition switch to the RUN position.
  6. Rotate the right front drive wheel by hand.
  7. Observe the DMM display.

Can a voltage greater than the specified value be obtained?

0.5 V AC

Go to Step 14

Go to Step 4

4

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

Is the circuit resistance within the specified range?

1530-1870 ohms

Go to Step 8

Go to Step 5

5

Is the circuit resistance greater than the specified value?

1870 ohms

Go to Step 11

Go to Step 6

6

  1. Leave the DMM test leads connected.
  2. Disconnect the A/T OSS connector at the transmission.

Is the circuit resistance less than the specified value?

1530 ohms

Go to Step 7

Go to Step 13

7

Inspect circuits 400 and 401 for being shorted together.

Refer to General Electrical Diagnosis .

Did you find and correct the condition?

--

Go to Step 15

--

8

Inspect circuit 400 for short to ground.

Refer to General Electrical Diagnosis .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 9

9

  1. Reconnect the C1 and C2 PCM connectors.
  2. Select DC volts.
  3. Using the J 35616-A Connector Test Adapter Kit, connect the DMM test leads to terminals A and B of the A/T OSS connector end.
  4. Turn the ignition to the RUN position.

Does the DMM display system voltage?

--

Go to Step 10

Go to Step 12

10

Inspect circuit 400 for a short to power.

Refer to General Electrical Diagnosis .

Did you find and correct the condition?

--

Go to Step 15

--

11
  1. Inspect circuit 400 for an open.
  2. Inspect circuit 401 for an open.

Refer to General Electrical Diagnosis .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 13

12

  1. Remove the A/T OSS.
  2. Refer to Vehicle Speed Sensor Replacement .
  3. Inspect the A/T OSS and the transmission for the following:
    4. • Incorrect A/T OSS
    • A/T OSS damage
    • Excessive A/T OSS 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 15

--

13

Replace the A/T OSS.

Refer to Vehicle Speed Sensor Replacement .

Is the replacement complete?

--

Go to Step 15

--

14

Replace the PCM.

Refer to PCM Replacement/Programming .

Is the replacement complete?

--

Go to Step 15

--

15

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 2.5 seconds.
  4. Select Specific DTC. Enter DTC P0502.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1