DTC P0502. Buick Century 2001

For 1990-2009 cars only

Makes 🢒 Buick 🢒 2001 🢒 Century 🢒 Body and Accessories 🢒 Body Control System 🢒 DTC P0502

Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

The vehicle speed sensor (VSS) system is a pulse generator consisting of a speed sensor assembly, located in the case extension, and a toothed vehicle speed sensor reluctor wheel, which is pressed onto the final drive carrier assembly. As the vehicle drives forward, the vehicle speed sensor reluctor wheel rotates. This rotation produces a variable AC signal in the pickup coil that is proportional to vehicle speed. The PCM uses this signal in order to calculate vehicle speed, shift timing and gear ratios.

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 Running the DTC

•	No MAP sensor DTC P0106, P0107, P0108, P1106 or P1107.

•	No TP sensor DTC P0121, P0122, P0123, P1121 or P1122.

•	No AT ISS DTC P0716 or P0717.

•	No TFP manual valve position switch DTC P1810.

•	The TP angle is greater than 12%.

•	The engine torque is 55-400 N·m (40-300 lb ft).

•	The transmission is not in PARK or NEUTRAL.

•	The input shaft speed is greater than 1500 RPM.

Conditions for Setting the DTC

The output shaft speed is less than 150 RPM for 2.5 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 shift adapts.

•	The PCM calculates vehicle speed from the AT input shaft speed sensor for shift timing.

•	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.

This step tests the ability of the VSS to produce an AC voltage. This step also verifies the integrity of the wiring to the PCM.

This step tests the VSS circuit for correct resistance.

DTC P0502 Vehicle Speed Sensor Circuit Low Input

Step

Action

Value(s)

Yes

Did you perform the Powertrain Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Engine Controls (3.1 L) or Diagnostic System Check - Engine Controls (3.8 L) in Engine Controls

Install a Scan Tool .
Turn ON the ignition switch with the engine OFF.

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.

Record the Freeze Frame and Failure Records.
Clear the DTCs.

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.

Raise and support the drive wheels.
Start and idle the engine.
Place the transmission in DRIVE.
Monitor Transmission OSS on the Scan Tool .
With the drive wheels rotating, increase and decrease the throttle position.

Does the Transmission OSS RPM increase when wheel speed increases?

Go to Intermittent Conditions (3.1 L) or Intermittent Conditions (3.8 L) in Engine Controls

Go to Step 3

Turn OFF the ignition.
Disconnect the PCM connector C1.
Using the J 35616 connector test adapter kit, connect the J 39200 digital multimeter (DMM) between terminals C1-64 and C1-65 of the PCM harness connector.
Select AC volts on the J 39200 DMM.
Turn ON the ignition with the engine OFF.
Place the range selector in a DRIVE range or NEUTRAL.
Rotate the right front drive wheel by hand, while observing the J 39200 DMM display.

Does the voltage measure greater than the specified value?

0.4 V AC

Go to Step 15

Go to Step 4

Leave the J 39200 DMM test leads connected between terminals C1-64 and C1-65 of the PCM harness connector.
Select ohms on the J 39200 DMM.
Measure the resistance of the complete VSS circuit.

Is the circuit resistance within the specified range?

1650-3180 ohms

Go to Step 8

Go to Step 5

Is the circuit resistance greater than the specified value?

3180 ohms

Go to Step 11

Go to Step 6

Leave the J 39200 DMM test leads connected between terminals C1-64 and C1-65 of the PCM harness connector.
Disconnect the VSS connector at the transmission.
Test the high signal circuit (CKT 400) and the low signal circuit (CKT 401) of the VSS for a short together.

Refer to Circuit Testing in Wiring Systems.

Are the signal and ground circuits shorted together?

Go to Step 7

Go to Step 14

Repair the short between the high signal circuit (CKT 400) and the low signal circuit (CKT 401).

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 16

Test the high signal circuit (CKT 400) of the VSS for a short to ground between the PCM and the VSS.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 9

Reconnect the C1 PCM connector.
Select DC volts on the J 39200 DMM.
Using the J 35616 connector test adapter kit, connect the J 39200 DMM between terminals A and B of the VSS vehicle harness.
Turn ON the ignition with the engine OFF.

Does the J 39200 DMM display greater than the specified voltage?

1.0 V

Go to Step 10

Go to Step 13

Repair the short to power in the high signal circuit (CKT 400).

Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 16

Test the high signal circuit (CKT 400) of the VSS for an open between the PCM and the VSS.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 12

Test the low signal circuit (CKT 401) of the VSS for an open between the PCM and the VSS.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 16

Go to Step 14

Remove the VSS.

Refer to Vehicle Speed Sensor Replacement .

Inspect the VSS and the transmission for the following:

•	Incorrect VSS

•	VSS damage

•	Excessive runout in the final drive carrier assembly

•	Excessive VSS to speed sensor rotor gap

•	Incorrect speed sensor rotor alignment

•	Speed sensor rotor damage

Repair any of the above items as necessary.

Refer to Transmission Overhaul in the 4T65-E Section of the Transmission Unit Repair Manual.

Did you find and correct the condition?

Go to Step 16

Go to Step 14

Replace the VSS.

Refer to Vehicle Speed Sensor Replacement .

Did you complete the replacement?

Go to Step 16

Replace the PCM.

Refer to Powertrain Control Module Replacement (3.1 L) or Powertrain Control Module Replacement (3.8 L) in Engine Controls.

Did you complete the replacement?

Go to Step 16

Perform the following procedure in order to verify the repair:

Select DTC.
Select Clear Info.
Drive the vehicle.
Ensure that the Transmission OSS is greater than 250 RPM for at least 2 seconds.
Select Specific DTC.
Enter DTC P0502.

Has the test run and passed?

System OK

Go to Step 1