DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input. Chevrolet Beretta 1996

For 1990-2009 cars
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

Vehicle speed is provided to the Powertrain Control Module (PCM) by the Vehicle Speed Sensor Assembly (VSS Assy.), which is a Permanent Magnet (PM) generator mounted to the transmission case. The PM generator produces an AC voltage as the transmission's speed sensor rotor teeth pass in front of the sensor's magnet. The AC voltage level increases as the speed of the vehicle increases. The PCM converts the AC voltage into a digital signal. The PCM uses the signal to calculate the vehicle speed, and when to apply the Torque Converter Clutch (TCC).

When the PCM detects a low vehicle speed and there is a high engine speed in a drive range, then DTC P0502 sets. DTC P0502 is a type B DTC.

### Conditions for Setting the DTC

• | No MAP DTCs P0107 or P0108

• | No TP DTCs P0122 or P0123

• | The transmission is in a drive range.

• | The TP angle is 18-50%.

• | The engine vacuum is 0-30 kPa.

• | The engine speed is 2950-4800 RPM.

• | The vehicle speed is 3.2 km/h (2 mph), or less.

• | All of the above conditions are met for two seconds.

### Action Taken When the DTC Sets

The PCM illuminates the Malfunction Indicator Lamp (MIL), after two consecutive trips with a failure reported.

### Conditions for Clearing the MIL/DTC

• | The PCM turns OFF the MIL after three consecutive ignition cycles 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.

### Diagnostic Aids

• | Inspect for Electromagnetic Interferences (EMI) induced on circuit 400 and 401 by an improperly routed harness.

• | Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring for poor electrical connections at the VSS Assy. Look 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

• | When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.

### Test Description

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

1. This step inspects for a vehicle speed signal.

2. This step tests for AC voltage from the VSS Assy. at the PCM.

3. This step measures the VSS Assy. resistance. If the resistance is too high or too low, the VSS Assy. must be replaced.

4. The signal voltage on circuit 400 must be greater than 4.5 volts.

5. This step verifies that the PCM has the correct, or latest, calibration.

6. This step tests for an open on circuit 401.

7. Replace the PCM only after you have completed the preceding diagnostic steps.

#### DTC P0502

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check

2

Notice: Ensure that the battery is fully charged. An under charged battery may cause incorrect test readings.

1. Install the scan tool.
2. With the engine OFF, turn the ignition switch to the RUN position.

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.

3. Record the DTC Freeze Frame and Failure Records.

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.

4. Raise and support the drive wheels.
5. Start and idle the engine.
6. Place the transmission in drive range.
7. Select output speed on the scan tool.

With the drive wheels rotating, does the transmission output speed increase when the wheel speed increases?

--

Go to Diagnostic Aids

Go to Step 3

3

1. Turn the ignition OFF.
2. Disconnect the C3 (Blue) PCM connector.
3. Using the J 35616-A -A Connector Test Adapter Kit, connect a voltmeter from terminal C3-07 to terminal C3-08 of the PCM connector.
4. Select AC volts on the voltmeter.
5. Rotate the drive wheels. Observe the voltmeter display.

Is the voltage greater than the specified value?

0.5V AC

Go to Step 6

Go to Step 4

4 | Connect an ohmmeter from terminal C3-07 to terminal C3-08 of the PCM connector. Is the resistance within the specified range? | 139-376ohms | Go to Step 6 | Go to Step 5

5

1. Disconnect the VSS Assy. connector.
2. Connect a jumper wire from terminal A to terminal B of the VSS Assy. connector.

Is the resistance equal or less than the specified value?

0.5ohms

Go to Step 12

Go to Step 7

6

1. Reconnect the C3 (Blue) connector to the PCM.
2. Disconnect the VSS Assy. connector at the transmission.
3. Using the J 35616-A -A Connector Test Adapter Kit, connect a voltmeter from terminal A of the VSS Assy. harness connector to a known good ground.
4. Select DC volts.
5. With the engine OFF, turn the ignition switch to the RUN position.

Is the voltage greater than the specified value?

4.5V AC

Go to Step 8

Go to Step 7

7

1. Inspect circuit 400 for an open or short to ground.
2. Repair the circuit if you find the condition.

Refer to Troubleshooting Procedures, Section 8.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

8 | Connect a test lamp from battery power (B+) to terminal B of the VSS Assy. harness connector. Is the test lamp ON? | -- | Go to Step 9 | Go to Step 11

9

1. Inspect the PCM for the latest calibration change.
2. Inspect the PCM for an incorrect calibration.

Refer to the current Service Bulletin.

Is the calibration correct for the vehicle?

--

Go to Step 13

Go to Step 10

10 | Update the PCM with the latest calibration. Refer to Powertrain Control Module/EEPROM Replacement/Programming , Section 6. Is the calibration update complete? | -- | Go to Step 14 | --

11

1. Inspect circuit 401 for an open.
2. Repair the circuit if you find the condition.

Refer to Troubleshooting Procedures, Section 8.

Did you find and correct the condition?

--

Go to Step 14

--

12 | Replace the VSS Assy. Refer to Vehicle Speed Sensor Assembly Replacement, in On-Vehicle Service. Is the replacement complete? | -- | Go to Step 14 | --
13 | Replace the PCM. Refer to Powertrain Control Module/EEPROM Replacement/Programming , Section 6. Is the replacement complete? | -- | Go to Step 14 | --

14

In order to verify your repair, perform the following procedure:

1. Select DTC.
2. Select Clear Info.
3. Drive the vehicle faster than 3 km/h (2 mph) for 2 seconds.
4. Select Specific DTC. Enter DTC P0502.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1