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Makes 🢒 Chevrolet 🢒 1997 🢒 Lumina 🢒 DTC 🢒 DTC P0503 Vehicle Speed Sensor (VSS) Circuit Intermittent

DTC P0503 Vehicle Speed Sensor (VSS) Circuit Intermittent 3.1L


Object Number: 58040 Size: SF
Automatic Transmission Controls Schematics
Automatic Transmission Components

Circuit Description

The Vehicle Speed Sensor (VSS) is a Permanent Magnet (PM) generator attached to the transmission case extension. The final drive assembly has a toothed wheel (VSS rotor). As the final drive assembly rotates, an AC voltage is induced and transmitted to the Powertrain Control Module (PCM).

The PCM converts the induced AC voltage into a digital signal. The PCM uses the vehicle speed in order to determine the shift timing, the TCC apply and release, and the gear ratio calculations. The VSS voltage varies from 0.5 volts AC at 100 RPM to more than 100 volts AC at 6000 RPM. The VSS resistance is 981-1864 ohms.

When the PCM detects a low vehicle speed with a high engine speed while in a drive range, then DTC P0503 sets. DTC P0503 is a type A DTC.

Conditions for Setting the DTC
    • The engine speed is more than 500 RPM for 5 seconds.
    • The engine is not in fuel shut off.
    • More than 6 seconds has elapsed since the last gear change.
    • The output speed does not rise more than 1000 RPM within 2 seconds.
    • The transmission is not in Park or Neutral.
    • The output speed drops more than 1500 RPM within 2 seconds.

Action Taken When the DTC Sets
    • The transmission defaults to 3rd gear.
    • The PCM inhibits TCC operation.
    • 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.
    • 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
    • Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring at the transmission 7-way connector. 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 verifies that the PCM is receiving a signal from the vehicle speed sensor.

    2.

  2. This step verifies that no opens exist in the circuitry from the vehicle speed sensor to the PCM connector.

    3.

  3. This step performs a resistance test on the VSS circuits from the PCM connector.

DTC P0503 Vehicle Speed Sensor Circuit (VSS) Low Input

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 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 erases the stored Freeze Frame and Failure Records from the PCM.

  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 range.
  7. Select Output Speed on the scan tool.

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

--

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn the ignition switch OFF.
  2. Disconnect the connector C1 on the PCM.
  3. Connect a J 39200 Digital Multimeter (DMM) from terminal 6 to terminal 47 of the PCM connector.
  4. Select AC volts on the DMM.
  5. Rotate the drive wheels.

Is the voltage more than the specified value?

0.5 V

Go to Step 4

Go to Step 6

4

Use the scan tool to find the most current calibration ID. Refer to Service Bulletins.

Does the ID number match?

--

Go to Step 13

Go to Step 5

5

Update the PCM with the latest calibration. Refer to Powertrain Control Module Replacement/Programming , Section 6.

Is the calibration update complete?

--

Go to Step 14

--

6
  1. Remove the VSS. Refer to Vehicle Speed Sensor, in On-Vehicle Service.
  2. Connect a J 39200 Digital Multimeter (DMM) from terminal A to terminal B of the VSS.
  3. Select ohms on the DMM.

Is the measured resistance within the specified range?

981 ohms to 1864 ohms

Go to Step 7

Go to Step 12

7
  1. Install the VSS. Refer to Vehicle Speed Sensor, in On-Vehicle Service.
  2. Connect a J 39200 Digital Multimeter (DMM) from terminal 6 to terminal 47 of the PCM connector.
  3. Select ohms on the DMM.

Does the J 39200 DMM display a value greater than the specified value?

1864 ohms

Go to Step 8

Go to Step 9

8
  1. Inspect circuit 400 and circuit 401 for an open.
  2. Repair the circuits if necessary.

Refer to Troubleshooting Procedures, Section 8.

Did you find and correct a problem?

--

Go to Step 14

--

9

Does the J 39200 DMM display a value less than the resistance specified?

981 ohms

Go to Step 10

Go to Step 11

10
  1. Inspect circuits 400 and 401 for a short together.
  2. Repair the circuits if necessary.

Refer to Troubleshooting Procedures, Section 8.

Did you find and correct a problem?

--

Go to Step 14

--

11
  1. Inspect circuits 400 and 401 for a short to ground.
  2. Repair the circuits if necessary.

Refer to Troubleshooting Procedures, Section 8.

Did you find and correct a problem?

--

Go to Step 14

Go to Step 13

12

Replace the vehicle speed sensor. Refer to VSS Replacement, in On-Vehicle Service.

Is the replacement complete?

--

Go to Step 14

--

13

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming , Section 6.

Is the replacement complete?

--

Go to Step 14

--

14

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

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions:
    4. • The engine speed more than 500 RPM for 5 seconds
    • The engine is not in fuel shut off.
    • More than 6 seconds has elapsed since the last gear change.
    • No output speed drop more than 500 RPM within 5 seconds.
    • Output speed is more than 1000 RPM for 2 seconds.
  4. Select Specific DTC. Enter DTC P0503.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1