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 low vehicle speed with a high engine speed while in a drive range, then DTC P0502 sets. DTC P0502 is a type B DTC.
Conditions for Setting the DTC
| • | No MAP DTCs P0106, P0107, P0108 P1106 or P1107. |
| • | No TP DTCs P0121, P0122, P0123, P1121 or P1122. |
| • | The transmission is not in Park or Neutral. |
| • | The input speed is more than 1500 RPM. |
| • | The throttle angle is more than 12%. |
| • | The MAP is 0-105 kPa (0-15 psi). |
| • | The engine torque is 55-200 N·m (40-150 lb ft). |
| • | The output speed is less than 150 RPM for 2.5 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the Malfunction Indicator Lamp (MIL). |
| • | The PCM commands maximum line pressure. |
| • | The PCM disables shift adapts. |
| • | 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
| • | Check for PRNDL DTC P0705. DTC P0705 affects transmission operation. This may set DTC P0502 falsely. |
| • | 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, 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 there are no opens in the circuitry from the vehicle speed sensor to the PCM connector.
Important: Place the gear select lever into the Neutral position before rotating the wheel.
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 | 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. The Clear Info function will erase the data. 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 J 39200 DMM. Is the resistance between terminals 64 and 65 greater than the specified range? | 1864 ohms | |||
5 | Inspect circuits 400 (YEL) and 401 (PPL) for an open or a poor connection. Repair the circuits if necessary. Refer to General Electrical Diagnosis 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 |
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 a J 39200 DMM from terminal A to terminal B of the VSS. Is the measured resistance within the specified range? | 981ohms to 1864ohms | ||
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 4T65-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 |
