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 generates AC voltage varying from 0.5 volts at 100 RPM to more than 100 volts at 6000 RPM.
The PCM uses this signal to determine vehicle speed 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 |
When the PCM detects an unrealistic, large drop in vehicle 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 range change. |
| • | The output speed does not rise more than 500 RPM within 2 seconds. |
| • | The transmission is not in Park or Neutral. |
| • | The output speed drops more than 1,500 RPM within 2 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the Malfunction Indicator Lamp (MIL). |
| • | The transmission defaults to 3rd gear. |
| • | The PCM inhibits TCC operation. |
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
| • | Check for Electromagnetic Interference (EMI) in circuits 400 and 401. EMI may be induced if the harness is routed along the spark plug wires. |
| • | 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 |
| • | When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change. |
| • | Ensure that the VSS is securely tightened to the case extension. |
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 no opens exist 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 | Were you sent here from the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls | |||||||||||
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. 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? | 0.4 V | |||||||||||||
Select ohms on the J 39200 DMM. Is the resistance between terminals 64 and 65 greater than the specified value? | 1864 ohms | |||||||||||||
5 | Inspect circuits 400 and 401 for an open. Repair the circuits if necessary. Refer to General Electrical Diagnosis Procedures in Wiring Systems. Was a condition found and corrected? | -- | ||||||||||||
6 | Does the J 39200 DMM display a value less than the resistance specified? | 981 ohms | ||||||||||||
7 | Inspect circuits 400 and 401 for a short together. Repair the circuits if necessary. Refer to General Electrical Diagnosis Procedures in Wiring Systems. Was a condition found and corrected? | -- | ||||||||||||
8 |
Is either resistance lower than the specified value? | 50 K ohms | ||||||||||||
9 | Inspect circuits 400 and 401 for a short to ground. Repair the circuits if necessary. Refer to General Electrical Diagnosis Procedures in Wiring Systems. Was a condition found and corrected? | -- | ||||||||||||
10 | Remove the VSS and connect a J 39200 DMM from terminal A to terminal B of the VSS. Is the measured resistance within the specified range? | 981-1864 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 Transmission Overhaul in the 4T60-E Section of the Transmission Unit Repair Manual. | 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 |
