DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input Gas Only
Circuit Description
The Output Shaft Speed Sensor (OSS Sensor), which is a Permanent Magnet (PM) generator, gives the vehicle speed information to the Vehicle Control Module (VCM). The PM generator produces a pulsing AC voltage. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The VCM then converts the pulsing voltage to vehicle speed. The vehicle speed is used for calculations. A scan tool can display the vehicle speed.
If the VCM detects a low vehicle speed and there is a high engine speed in a drive gear range, DTC P0502 sets. DTC P0502 is a type D DTC. For California emissions, DTC P0502 is a type B DTC.
Conditions for Setting the DTC
| • | No Throttle Position (TP) Sensor DTCs P0122 or P0123. |
| • | No TFP Val. Position Sw. DTC P1810 |
| • | No A/T ISS Sensor low DTC P0716 or P0717. |
| • | The engine torque must be 60 N·m (80 lb ft) to the following: |
| - | 470 N·m (375 lb ft) 5.7L |
| - | 627 N·m (500 lb ft) 7.4L |
| • | The A/T ISS is greater than 2500 RPM. |
| • | The transmission is not in Park or Neutral. |
| • | The engine is running more than 475 RPM for 7 seconds. |
| • | The OSS is less than 200 RPM for at least 3 seconds. |
Action Taken When the DTC Sets
| • | The VCM commands maximum line pressure. |
| • | The VCM freezes the shift adapts. |
| • | The VCM defaults a calculated output speed value by using the Input Speed Sensor values. |
| • | For California emissions, the VCM illuminates the Malfunction Indicator Lamp (MIL). |
Conditions for Clearing the MIL/DTC
| • | For California emissions, the VCM turns off the MIL after three consecutive ignition cycles without a failure reported. |
| • | A scan tool can clear the DTC from the VCM history. The VCM clears the DTC from the VCM history if the vehicle completes 40 warm-up cycles without a failure reported. |
| • | The VCM cancels the DTC default actions when the fault no longer exists and the ignition is cycled OFF long enough to power down the VCM. |
Diagnostic Aids
| • | DTC P0502 sets when no vehicle speed is detected at the start off. |
| • | Inspect the wiring for poor electrical connections at the VCM. Inspect the wiring for poor electrical connections at the transmission 20-way connector. Look for the following problems: |
| - | A bent terminal |
| - | A backed out terminal |
| - | A damaged terminal |
| - | Poor terminal tension |
| - | A chafed wire |
| - | A broken wire inside the insulation. |
| • | When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. |
| • | First diagnose and clear any engine DTCs or TP Sensor codes. Then inspect for any transmission DTCs that may have reset. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for voltage in the 822 ground circuit.
-
This step tests the 5-volt and ground circuit of the VCM.
-
This step tests the integrity of the OSS Sensor.
-
This step tests the OSS circuit.
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 (4.3L) Powertrain On Board Diagnostic (OBD) System Check (5.7L and 7.4L) | |
2 |
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 erases the stored Freeze Frame and Failure records from the VCM. | -- | Go to Diagnostic Aids | |
3 |
Is the voltage within the specified value? | 4.0-5.1 volts DC | ||
With the ignition switch in the RUN position, measure the voltage between terminal B of the OSS Sensor harness and a good ground. Is the voltage less than the specified value? | 0.2 volts | |||
5 | Was the voltage reading in Step 3 greater than the specified value? | 5.1 volts | ||
With the ignition switch in the Run position, measure the voltage between terminals A and B of the OSS Sensor harness connector. Is the voltage within the specified value? | 4.0-5.1 volts | |||
7 |
Note: 4 wheel drive vehicles use an in-line connector between the engine harness and the OSS Sensor harness at the transfer case. Inspect circuit 821 for high resistance or an open circuit. Refer to Electrical Diagnosis, Section 8. Did you find a problem? | -- | ||
8 |
Note: 4 wheel drive vehicles use an in-line connector between the engine harness and the OSS Sensor harness at the transfer case. Inspect circuit 822 for an open circuit between the connector and the VCM. Did you find a problem? | -- | ||
9 | Inspect circuit 821 for a short to ground. Did you find a problem? | -- | ||
10 | Using the DMM, measure the resistance between terminals A and B of the OSS Sensor. Is the resistance within the specified value? | 1470-2820ohms | ||
Is the voltage greater than the specified value? | 0.5 volts AC | |||
12 |
Did you find a problem? | -- | ||
Is the voltage greater than the specified value? | 0.5 volts AC | -- | ||
14 |
Did you find a problem? | -- | ||
15 |
Refer to Transmission Overhaul , in Unit Repair. Did you find a problem? | -- | ||
16 | Replace the VCM. Refer to VCM Replacement/Programming (With KS Calibration PROM) , Section 6. Is the replacement complete? | -- | -- | |
17 | Replace the OSS Sensor. Refer to Speed Sensor Replacement, in On-Vehicle Service. Is the replacement complete? | -- | -- | |
18 | In order to verify your repair, perform the following procedure:
Has the test run and passed? | -- | System OK |
