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) system is a pulse generator consisting of a speed sensor assembly, located in the case extension, and a toothed vehicle speed sensor reluctor wheel, which is pressed onto the final drive carrier assembly. As the vehicle drives forward, the vehicle speed sensor reluctor wheel rotates. This rotation produces a variable AC signal in the pickup coil that is proportional to vehicle speed.

The AC signal generated has a frequency and amplitude (voltage). The PCM uses the frequency to calculate the vehicle speed. The voltage portion of the signal is used for diagnostic purposes only. The voltage will vary from 0.5 volts AC at 100 RPM to as much as 200 volts AC at 6000 RPM.

This information is then sent to the PCM to indicate how fast the vehicle is traveling and to develop the shift pattern for the transmission. Other systems also use VSS information:

• | TCC apply and release

• | Cruise control system

• | Fuel delivery systems

If the PCM detects a large change in vehicle speed in a short period of time, then DTC P0503 sets. DTC P0503 is a type B DTC.

### Conditions for Running the DTC

• | The engine speed is more than 500 RPM for 5 seconds and not in fuel shut off.

• | The transmission is not in PARK or NEUTRAL.

• | The time since the last gear range change is more than 6 seconds.

• | No output shaft speed rise greater than 250 RPM in 2 seconds.

### Conditions for Setting the DTC

The output shaft speed drops greater than 1500 RPM in 3 seconds.

### 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 maximum line pressure.

• | The PCM freezes shift adapts.

• | The PCM calculates vehicle speed from the AT input shaft speed sensor for shift timing.

• | The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.

• | 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 can clear the MIL/DTC.

• | The PCM clears the DTC from the PCM history if the vehicle completes 40 consecutive 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 connectors at the controller, the component and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

• | Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Wiring Systems.

• | Check for electromagnetic interference (EMI) in circuits 400 (YEL) and 401 (PPL). EMI may be induced by a misrouted wiring harness along the spark plug wires.

• | Too much runout in the final drive carrier assembly may set DTC P0503.

### Test Description

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

1. This step test the ability of the VSS to produce an AC current. This step also verifies the integrity of the wiring to the PCM.

2. This step test the VSS circuit for correct resistance.

#### DTC P0503 Vehicle Speed Sensor Circuit Intermittent

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain Diagnostic System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls
2 |

1. Install a Scan Tool .
2. Turn the ON the ignition switch with the engine OFF.

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 Freeze Frame and Failure Records.
4. Clear the DTCs.

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. Raise and support the drive wheels.
6. Start and idle the engine.
7. Place the transmission in DRIVE.
8. Monitor Transmission OSS on the Scan Tool .
9. With the drive wheels rotating, increase and decrease the throttle position.

Does the Transmission OSS RPM increase when wheel speed increases?

--

Go to Diagnostic Aids

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the PCM connector C1.
3. Using the J 35616 connector test adapter kit, connect the J 39200 digital multimeter (DMM) between PCM terminals C1-64 and C1-65.
4. Select AC volts on the J 39200 DMM.
5. Turn ON the ignition with the engine OFF.
6. Place the range selector in a DRIVE range or NEUTRAL.
7. Rotate the right front drive wheel by hand, while observing the J 39200 DMM display.

Does the voltage measure greater than the specified value?

0.4 volts AC

Go to Step 15

Go to Step 4

4 |

1. Leave the J 39200 DMM test leads connected.
2. Select ohms on the J 39200 DMM.
3. Measure the resistance of the complete VSS circuit from PCM connector terminal C1-64 to C1-65.

Is the circuit resistance within the specified range?

1650-2200 ohms @ 20°C (68°F)

2360-3180 ohms @ 150°C (302°F)

Go to Step 8

Go to Step 5

5 | Is the circuit resistance greater than the specified value? | 3180 ohms | Go to Step 11 | Go to Step 6
6 |

1. Leave the J 39200 DMM test leads connected.
2. Disconnect the VSS connector at the transmission.
3. Test the signal circuit (CKT 400) and the ground circuit (CKT 401) of the VSS for a short together. Measure from PCM connector terminals C1-64 to C1-65.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Are the signal and ground circuits shorted together?

--

Go to Step 7

Go to Step 14

7 | Repair the short between the signal circuit (CKT 400) and the ground circuit (CKT 401). Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | --
8 | Test the signal circuit (CKT 400) of the VSS for a short to ground between the PCM and the VSS. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 9
9 |

1. Reconnect the C1 PCM connector.
2. Select DC volts on the J 39200 DMM.
3. Using the J 35616 connector test adapter kit, connect the J 39200 DMM test leads to terminals A and B of the VSS vehicle harness.
4. Turn ON the ignition with the engine OFF.

Does the J 39200 DMM display greater than the specified voltage?

1.0 V

Go to Step 10

Go to Step 13

10 | Repair the short to power in the signal circuit (CKT 400). Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | --
11 | Test the signal circuit (CKT 400) of the VSS for an open between the PCM and the VSS. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 12
12 | Test the ground circuit (CKT 401) of the VSS for an open between the PCM and the VSS. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14
13 |

1. Remove the VSS.

Refer to Vehicle Speed Sensor Replacement .

2. Inspect the VSS and the transmission for the following:

• | Incorrect VSS

• | VSS damage

• | Excessive VSS to speed sensor rotor gap

• | Incorrect speed sensor rotor alignment

• | Speed sensor rotor damage

3. Repair any of the above items as necessary.

Refer to Transmission Overhaul in the 4T65-E Section of the Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 16

Go to Diagnostic Aids

14 | Replace the VSS. Refer to Vehicle Speed Sensor Replacement . Did you complete the replacement? | -- | Go to Step 16 | --
15 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming in Engine Controls. Did you complete the replacement? | -- | Go to Step 16 | --
16 | Perform the following procedure in order to verify the repair:

1. Select DTC.
2. Select Clear Info.
3. Drive the vehicle so that the Transmission OSS is greater than 300 RPM for at least 2 seconds.
4. Select Specific DTC.
5. Enter DTC P0503.

Has the test run and passed?

--

System OK

Go to Step 1