Circuit Description
The Vehicle Speed Sensor (VSS) system is a pulse generator consisting of a speed sensor assembly, located in the case, and a toothed speed sensor rotor, which is pressed onto the final drive assembly. As the vehicle drives forward, the speed sensor rotor also rotates. This rotation produces a variable voltage signal in the pickup coil that is proportional to vehicle speed.
The VSS will generate AC voltage that will vary from 0.5 volts at 100 RPM to more than 100 volts 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 Setting the DTC
| • | The transmission is not in Park or Neutral. |
| • | The time since the last gear range change is more than 6 seconds. |
| • | The engine speed is more than 500 RPM, for 5 seconds, and not in fuel shut off. |
| • | No output speed rise greater than 500 RPM in 2 seconds. |
| • | The output speed drops more than 1500 RPM in 3 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the Malfunction Indicator Lamp (MIL). |
| • | 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 trips 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 at the PCM, the Vehicle Speed Sensor (VSS) connector and all other circuit connecting points 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 |
| - | Moisture intrusion |
| - | Corrosion |
| • | 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 condition 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.
-
This step verifies that the PCM is receiving a signal from the vehicle speed sensor.
-
This step verifies that there are no opens in the circuitry from the vehicle speed sensor to the PCM connector.
-
This step performs a resistance test on the VSS circuits from the PCM connector.
Step | Action | Value(s) | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls | |||||||||||||
Important: Before clearing the DTC(s), 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. 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. With drive wheels rotating, does transmission output speed increase when wheel speed increases? | -- | Go to Diagnostic Aids | ||||||||||||||
Is the measured voltage greater than the specified value? | 0.5 volts | |||||||||||||||
Select ohms on the DMM. Is the resistance between terminals 64 and 65 greater than the specified range? | 1864 ohms | |||||||||||||||
5 |
Refer to General Electrical Diagnosis in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Was a condition found and corrected? | -- | ||||||||||||||
6 | Does the DMM display a value less than the resistance specified? | 981 ohms | ||||||||||||||
7 |
Refer to General Electrical Diagnosis in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Did you find and correct a condition? | -- | ||||||||||||||
8 |
Is either resistance lower than the specified value? | 50 K ohms | ||||||||||||||
9 |
Refer to General Electrical Diagnosis in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Was a condition found and corrected? | -- | ||||||||||||||
10 | Remove the VSS and connect the DMM from terminal A to terminal B of the VSS. Is the measured resistance within the specified range? | 981 ohms to 1864 ohms | ||||||||||||||
11 | Remove the VSS and inspect the Sensor Ring on the Final Drive Carrier Assembly for damage or misalignment. Was a condition found? | -- | Go to Unit Repair | Go to Diagnostic Aids | ||||||||||||
12 | Replace the Vehicle Speed Sensor. Refer to Vehicle Speed Sensor Replacement . Is the replacement complete? | -- | -- | |||||||||||||
13 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming in Engine Controls. Is the replacement complete? | -- | -- | |||||||||||||
14 | In order to verify your repair, perform the following procedure:
Has the test run and passed? | -- | System OK |
