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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2005 🢒 DeVille 🢒 Accessories 🢒 Navigation Systems 🢒 DTC P0502

Object Number: 1492402 Size: SF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Control Module References

Circuit Description

The vehicle speed sensor (VSS) is a permanent magnet generator attached to the transmission case. The final drive assembly has a toothed wheel, VSS rotor. As the final drive assembly rotates, an AC voltage is induced and transmitted to the powertrain control module (PCM). The PCM converts the AC voltage into a digital signal. The PCM uses the vehicle speed to determine shift timing, torque converter clutch apply and release, and gear ratio.

If the PCM detects a low vehicle speed and a high transmission input shaft speed while in a drive range, then DTC P0502 sets. DTC P0502 is a type B DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Voltage

Conditions for Running the DTC
    • No MAF DTCs P0101, P0102 or P0103.
    • No MAP DTCs P0106, P0107 or P0108.
    • No TP DTCs P0121, P0122 or P0123.
    • No VSS DTC P0503.
    • No AT ISS DTCs P0716 or P0717.
    • The engine run time is greater than 5 seconds.
    • The transmission is not in PARK or NEUTRAL.
    • The TP angle is 12 percent or greater.
    • The engine torque is 60-395 N·m (44-291 lb ft).
    • TOS is less than 90 RPM for 3 seconds.
    • The transmission input shaft speed is 1,000-5,000 RPM.
    • Trans. Temp. is 0°C (32°F) or greater.
    • TCC slip speed is greater than -5 RPM.

Conditions for Setting the DTC
    • LD8: The transmission output shaft speed is 280 RPM or less for 3 seconds.
    • L37: The transmission output shaft speed is 334 RPM or less for 3 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
    • The PCM commands maximum line pressure.
    • The PCM freezes transmission adaptive functions.
    • The PCM inhibits TCC.
    • The PCM calculates vehicle speed from the automatic transmission input, shaft, speed sensor and commanded gear.
    • The PCM applies the TCC in 3rd gear when in Hot Mode.
    • The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
    • The PCM stores DTC P0502 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
    • A scan tool can clear the MIL/DTC.
    • The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
    • The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM.

Test Description

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

  1. This step tests for DTCs and for a vehicle speed signal. It is important to record Freeze Frame and Failure Record information before proceeding further.

    2.

  2. This step tests for a resistance value greater than 1,911 ohms which would indicate an open in the high signal circuit, the low signal circuit or the VSS.

DTC P0502

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM.

  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.

    5. 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.

  5. Raise and support the drive wheels.
  6. Start and idle the engine.
  7. Place the transmission in DRIVE.
  8. Select Transmission OSS on the scan tool.

With the drive wheels rotating, does the Transmission OSS RPM increase when the wheel speed increases?

--

Go to Intermittent Conditions in Engine Controls

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Using the J 35616 GM Terminal Test Kit, connect the DMM between PCM terminals VSS high and VSS low signal circuits.
  4. Select AC volts on the DMM.

    5. Important: Place the gear select lever in the Neutral position before rotating the drive wheel.

  5. Rotate the right front drive wheel by hand.
  6. Observe the DMM display.

Can a voltage greater than the specified value be obtained?

0.5 V AC

Go to Step 14

Go to Step 4

4
  1. Leave the DMM test leads connected.
  2. Measure circuit resistance.

Does the resistance measure within the specified range?

1,260-1,911 ohms

Go to Step 8

Go to Step 5

5

Does the resistance measure greater than the specified value?

1,911 ohms

Go to Step 11

Go to Step 6

6
  1. Leave the DMM test leads connected.
  2. Disconnect the VSS connector at the transmission.

Does the resistance measure less than the specified value?

1,260 ohms

Go to Step 7

Go to Step 13

7

Test the high signal circuit and the low signal circuit of the VSS for being shorted together.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

--

8

Test the high signal circuit of the VSS for a short to ground.

Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 9

9
  1. Connect the PCM.
  2. Using the J 35616 , connect the DMM test leads to the VSS wiring harness connector end.
  3. Select DC volts on the DMM.
  4. Turn ON the ignition, with the engine OFF.

Does the DMM display system voltage?

--

Go to Step 10

Go to Step 12

10

Test the high signal circuit of the VSS for a short to voltage.

Refer to Testing for a Short to Voltage and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

--

11
  1. Test the high signal circuit of the VSS for an open.
  2. Test the low signal circuit of the VSS for an open.

Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 15

Go to Step 13

12
  1. Remove the VSS.

    2. Refer to Vehicle Speed Sensor Replacement .

  2. Inspect the VSS and the transmission for the following conditions:
    3. • Incorrect VSS
    • VSS damage
    • Excessive VSS to speed sensor rotor gap
    • Incorrect speed sensor rotor alignment
    • Speed sensor rotor damage
  3. Repair any of the above conditions as necessary.

Refer to Differential Carrier and Housing Removal in the 4T80-E section of the Transmission Unit Repair Manual.

Did you complete the repair?

--

Go to Step 15

--

13

Replace the VSS.

Refer to Vehicle Speed Sensor Replacement .

Did you complete the replacement?

--

Go to Step 15

--

14

Replace the PCM.

Refer to Control Module References in Computer/Integrating Systems.

Did you complete the replacement?

--

Go to Step 15

--

15

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle in order to achieve a Transmission OSS of greater than 1,855 RPM for 2 seconds.
  4. Select Specific DTC.
  5. Enter DTC P0502.

Has the test run and passed?

--

Go to Step 16

Go to Step 2

16

With the scan tool, observe the stored information, capture info. and DTC info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK