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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1999 🢒 Corvette 🢒 DTC 🢒 DTC P0503 Vehicle Speed Sensor (VSS) Circuit Intermittent

Object Number: 360635 Size: MF
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

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 (PM) generator. The PM generator produces a pulsing AC voltage as rotor teeth on the differential ring gear pass through the sensor's magnetic field. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The PCM converts the pulsing voltage to vehicle speed. The PCM uses the vehicle speed signal to determine shift timing and torque converter clutch (TCC) scheduling.

When the PCM detects an unrealistically large drop in vehicle speed, then DTC P0503 sets. DTC P0503 is a type B DTC.

Conditions for Running the DTC
    • No TFP manual valve position switch DTC P1810.
    • The time since the last gear range change is greater than 6 seconds.
    • The engine speed is greater than 300 RPM for 5 seconds.
    • The engine is not in fuel cutoff.
    • The transmission output speed rise does not exceed 600 RPM within 6 seconds.

Conditions for Setting the DTC

The transmission output speed drop is greater than 1300 RPM, for 3 seconds, when the transmission is not in PARK or NEUTRAL.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for setting the DTC are met.
    • The PCM commands second gear only.
    • The PCM commands maximum line pressure.
    • The PCM inhibits TCC engagement.
    • The PCM inhibits 4th gear if the transmission is in hot mode.
    • The PCM freezes shift adapts from being updated.
    • The PCM stores DTC P0503 in PCM history during the second consecutive trip in which the Conditions for setting the DTC are met.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
    • A scan tool clears the DTC from PCM history.
    • The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
    • The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids
    • Inspect the wiring at the PCM, the VSS connector and all other circuit connecting points for the following conditions:
       - A backed out terminal
       - A damaged terminal
       - Reduced 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 the rotor teeth on the differential ring gear for damage.

Test Description

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

  1. Disable the traction control system when performing this step. When the ignition switch is cycled OFF and then back ON, the traction control system defaults to ON.

    2.

  2. This step tests the VSS assembly circuit.

    3.

  3. This step tests the integrity of the VSS assembly.

DTC P0503 Vehicle Speed Sensor Circuit - Performance

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

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

    3. Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM.

  3. Record the Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Raise and support the rear axle assembly.
  6. Start the engine.
  7. Disable the traction control system.
  8. Place the transmission in D3 range.
  9. With the drive wheels rotating, slowly accelerate to 2000 RPM and hold (road test the vehicle if necessary).

Does the scan tool Transmission OSS drop or fluctuate more than the specified value?

1300 RPM

Go to Step 3

Go to Diagnostic Aids

3

  1. Turn the ignition OFF.
  2. Disconnect the PCM connector C2.
  3. Using the J 39200 digital multimeter (DMM) and the J 35616-A connector test adapter kit, measure the resistance between harness connector terminals C2-20 and C2-21.

Is the resistance within the specified range?

976-2354 ohms

Go to Step 4

Go to Step 6

4

Measure the resistance from terminal C2-21 to ground.

Is the resistance greater than the specified value?

50 K ohms

Go to Step 5

Go to Step 7

5

  1. Place the transmission in NEUTRAL.
  2. Select AC volts.
  3. Hold one rear wheel from turning.
  4. Rotate the other rear wheel by hand, ensuring that the driveshaft is turning.

Is the voltage greater than the specified value?

0.3 volts

Go to Step 10

Go to Step 9

6
  1. Disconnect the engine wiring harness from the VSS assembly.
  2. Measure the resistance of the VSS assembly.

Is the resistance within the specified range?

976-2354 ohms

Go to Step 8

Go to Step 9

7
  1. Inspect circuits 400 (YEL) and 401 (PPL) for a short to ground.

    2. Refer to General Electrical Diagnosis in Wiring Systems.

  2. Repair the circuits if necessary.

    3. Refer to Wiring Repairs in Wiring Systems.

Was a short to ground condition found?

--

Go to Step 11

Go to Diagnostic Aids

8
  1. Inspect circuits 400 (YEL) and 401 (PPL) for an open.

    2. Refer to General Electrical Diagnosis in Wiring Systems.

  2. Repair the circuits if necessary.

    3. Refer to Wiring Repairs in Wiring Systems.

Was an open condition found?

--

Go to Step 11

Go to Diagnostic Aids

9

Replace the VSS assembly.

Refer to Vehicle Speed Sensor Replacement.

Is the replacement complete?

--

Go to Step 11

--

10

Replace the PCM. Refer to Powertrain Control Module/Throttle Actuator Control Module Replacement in Engine Controls.

Is the replacement complete?

--

Go to Step 11

--

11

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle ensuring that the transmission output speed drop is less than 500 RPM for 3 seconds and output speed is greater than 600 RPM for 3 seconds.
  4. Select Specific DTC.
  5. Enter DTC P0503.

Has the test run and passed?

--

System OK

Go to Step 1