For 1990-2009 cars
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts 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 Powertrain Control Module (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 6000 RPM. VSS resistance value is 981-1864 ohms.

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

### Conditions for Setting the DTC

• | The transmission is not in Park or Neutral.

• | The gear select lever change is more than 6 seconds.

• | The engine speed is more than 500 RPM.

• | Not in fuel shut off.

• | No output speed rise greater than 1000 RPM in 2 seconds.

• | The output speed drops more than 1500 RPM in 2 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the Malfunction Indicator Lamp (MIL) after 2 consecutive ignition cycles with a failure reported.

• | The PCM disables shift adapts.

• | The PCM commands maximum line pressure.

• | The PCM calculates vehicle speed from the Automatic Transmission Input Speed Sensor (A/T ISS) and from the 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 problems:

- | 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, massage the wiring harness while watching the test equipment for a change.

• | Check for an Electromagnetic Interference (EMI) induced on circuits 400 and 401 by a misrouted wiring harness along the 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 checks for a vehicle speed signal. It is important to record freeze frame or failure records information before proceeding further.

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

   This step checks for an AC voltage at the PCM.

3. This step performs a resistance check on circuit 400 and circuit 401 from the PCM to the VSS. The circuits must be checked for an open.

#### 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 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.

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 C1.
3. Connect a voltmeter from terminal 6 to terminal 47 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 7

Go to Step 4

4 | Connect an ohmmeter from terminal 6 to terminal 47 of the PCM connector. Does the ohmmeter display a value greater than the specified value? | 1864ohms | Go to Step 5 | Go to Step 6
5 |

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

Refer to Troubleshooting Procedures, Section 8.

Did you find and correct the problem?

--

Go to Step 12

Go to Step 8

6 | Does the ohmmeter display a value within the specified range? | 981-1864ohms | Go to Step 7 | Go to Step 8
7 |

1. Inspect circuit 400 for a short to ground.
2. Inspect circuit 401 for a short to ground.
3. Inspect circuits 400 and 401 for a short together.

Refer to Troubleshooting Procedures, Section 8.

Did you find and correct the problem?

--

Go to Step 12

Go to Step 8

8 |

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?

981-1864ohms

Go to Step 10

Go to Step 9

9 | Replace the VSS. Refer to Vehicle Speed Sensor Replacement, in On-Vehicle Service. Is the replacement complete? | -- | Go to Step 12 | --
10 |

1. Disconnect the C1 (Blue) connector from the Powertrain Control Module (PCM).
2. Inspect the PCM connector terminals for the following problems:

• | Damaged connector pins

• | Backed out connector pins

• | Weak terminal tension.

Did you find and correct a problem?

--

Go to Step 12

Go to Step 11

11 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming Section 6. Is the replacement complete? | -- | Go to Step 12 | --
12 | 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:

• | The transmission is not in Park or Neutral.

• | The gear select lever change is more than 6 seconds.

• | The engine speed is greater than 500 RPM.

• | Not in fuel shut off.

• | The output speed is greater than 1000 RPM for 2 seconds.

• | The output speed drop is less than 500 RPM in 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