DTC P0503 Vehicle Speed Sensor (VSS) Circuit Intermittent. Cadillac Concours 1996

For 1990-2009 cars
Automatic Transmission Components
Brake Switch, Solenoids, and VSS
Handling ESD Sensitive Parts Notice
OBD II Symbol Description Notice

### Circuit Description

The Vehicle Speed Sensor (VSS) is a Permanent Magnet (PM) generator attached to the transmission case. 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 PCM. The PCM converts the AC voltage into a digital signal. The PCM uses vehicle speed to determine shift timing, TCC apply and release and gear ratio. VSS voltage will vary from 0.5 volts AC at 100 RPM to more than 100 volts AC at 8000 RPM. VSS resistance value is between 1300-1950 ohms.

When the PCM detects a large change in vehicle speed, then DTC P0503 sets. DTC P0503 is a Type A DTC.

### Conditions for Setting the DTC

• | No MAF P0101, P0102 or P0103 DTCs are set.

• | No TP sensor P0121, P0122 or P0123 DTCs are set.

• | No Automatic Transmission Input (Shaft) Speed sensor P0716 or P0717 DTCs are set.

• | The ignition is in the RUN position for more than 2 seconds.

• | The gear select lever change is more than 3 seconds.

• | The engine speed is more than 500 RPM.

• | The TP angle is more than 12.8°.

• | Traction control is inactive.

• | The delivered torque is greater than 109 N·m (80 lb ft).

• | The vehicle speed drops more than 18 km/h (11 mph) in 0.012 seconds and input speed does not drop by 100 RPM within 0.125 seconds. (This condition must occur 10 times within 10 seconds.)

### Action Taken When the DTC Sets

• | The PCM illuminates the Malfunction Indicator Lamp (MIL).

• | SERVICE ENGINE SOON, SPEED SENSOR FAULT message displays on the Driver Information Center (DIC).

• | The PCM disables steady state adapts.

• | The PCM disables upshift adapts.

• | The PCM commands default line pressure.

• | The PCM inhibits the Torque Converter Clutch.

• | The PCM inhibits torque management.

• | The PCM disables the cruise control.

• | The PCM calculates vehicle speed from the Automatic Transmission Input (Shaft) Speed sensor and commanded gear.

### 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 for poor electrical connections at the VSS 2-way connector. Look for the following conditions:

- | A bent terminal

- | A backed out terminal

- | A damaged terminal

- | Poor terminal tension

- | A chafed wire

• | Inspect the engine wiring harness for pinched wires which may cause an intermittent. When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.

• | Check for Electromagnetic Interference (EMI) induced on circuits 400 and 401 by a misrouted wiring harness along spark plug wires.

• | Ensure that the VSS is tightened securely into the transmission case extension.

• | Too much runout in the final drive carrier may set DTC P0503. If you cannot find a problem with the VSS or its circuitry, replace the final drive carrier.

### Test Description

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

1. This Step ensures that the Powertrain On-Board Diagnostic System Check was performed.

2. This Step checks for DTCs. This Step checks for a vehicle speed signal. It is important to record freeze frame or failure records information before proceeding further.

3. Important: Place the gear select lever into the Neutral position before rotating the wheel.

   This Step checks for an AC voltage at the PCM.

4. This Step has the scan tool verify that the correct calibration is in the PCM.

5. This Step performs a resistance check on the VSS circuits from the PCM connector.

6. This Step verifies that the ohmmeter displays a resistance value greater than 1950 ohms. Circuit 400 and Circuit 401 must be checked for an open.

7. This Step verifies that the ohmmeter displays a value less than or equal to the specified VSS value. Resistance less than 1300 implies that the circuits are shorted together. Resistance within specification implies that circuit 400 or circuit 401 has a possible short to ground.

8. This Step performs a resistance check on the VSS, if no opens, shorts to ground or shorts together were found on the 400 or 401 circuits.

9. This Step verifies that the ohmmeter displays a resistance value less than or greater than that specified.

10. This Step replaces the PCM after testing the component and circuitry.

11. This Step road tests the vehicle to ensure that the repair is complete.

#### DTC P0503 Vehicle Speed Sensor Circuit (VSS) Intermittent

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to A Powertrain On Board Diagnostic (OBD) System Check

2

1. Install the scan tool (tech 1) .
2. With the engine OFF, turn the ignition switch to the RUN position.

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 or Failure Records.
4. Raise and support the drive wheels.

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.

5. Start the engine and idle the engine.
6. Place the transmission in drive range.
7. Select Trans OSS RPM on the scan tool.

With the drive wheels rotating, does the Trans OSS RPM increase when the wheel speed increases?

--

Go to Diagnostic Aids

Go to Step 3

3

1. Turn the ignition OFF.
2. Disconnect PCM connector C2.
3. Connect a voltmeter from terminal 7 to terminal 8 of the PCM connector.
4. Select AC volts on the voltmeter.
5. Rotate the drive wheels and observe the display.

Is the voltage greater than the specified value?

0.5V

Go to Step 4

Go to Step 6

4 | Use the scan tool to check for the most current calibration ID. Refer to Service Bulletins. Does the ID number match? | -- | Go to Step 12 | Go to Step 5
5 | Update the PCM with the latest calibration. Refer to the PCM Replacement/Programming . Is the calibration update complete? | -- | Go to Step 13 | --
6 | Connect an ohmmeter from terminal 7 to terminal 8 of the PCM connector. Does the ohmmeter display a value greater than the specified value? | 1950ohms | Go to Step 7 | Go to Step 8
7 | Inspect circuit 400 or circuit 401 for an open. Refer to Electrical Diagnosis, Section 8. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
8 | Does the ohmmeter display a value within (or less than) the specified range? | 1300-1950ohms | Go to Step 9 | Go to Step 10
9 | Inspect circuit 400 or circuit 401 for a short to ground or a short together. Refer to Electrical Diagnosis, Section 8. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10

10

1. Remove the VSS.
2. Connect an ohmmeter from terminal A to terminal B of the VSS.

Does the ohmmeter display a value within the specified range?

1300-1950ohms

Go to Step 12

Go to Step 11

11 | Replace the Vehicle Speed Sensor. Refer to VSS Replacement/Unit Repair. Is the replacement complete? | -- | Go to Step 13 | --
12 | Replace the PCM. Refer to PCM Replacement/Programming Section 6. Is the replacement complete? | -- | Go to Step 13 | --

13

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:

• | Drive the vehicle in D4.

• | Achieve a vehicle speed greater than 16 km/h (10 mph).

4. Select Specific DTC. Enter DTC P0503.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1