DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input. Oldsmobile Alero 2000

Test the signal circuit (CKT 400) and the ground circuit (CKT 401) of the AT OSS for being shorted together.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Test the signal circuit (CKT 400) of the AT OSS for a short to ground.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Reconnect PCM connectors C1 and C2 .
Select DC volts on the J 39200 DMM .
Using the J 35616 , connect the J 39200 DMM test leads to terminals A and B of the AT OSS wiring harness connector end.
Turn ON the ignition, with the engine OFF.

Does the DMM display system voltage?

Go to Step 10

Go to Step 12

Test the signal circuit (CKT 400) of the AT OSS for a short to voltage.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Test the signal circuit (CKT 400) of the AT OSS for an open.
Test the ground circuit (CKT 401) of the AT OSS for an open.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Remove the AT OSS.

Inspect the AT OSS and the transmission for the following conditions:

•	Incorrect AT OSS

•	AT OSS damage

•	Excessive AT OSS to speed sensor rotor gap

•	Incorrect speed sensor rotor alignment

•	Speed sensor rotor damage

Repair any of the above conditions as necessary.

Refer to Transmission Overhaul in the 4T40-E/4T45-E section of the Transmission Unit Repair Manual.

Did you complete the repair?

Replace the AT OSS.

Did you complete the replacement?

Replace the PCM.

Refer to Powertrain Control Module Replacement/Programming in Engine Controls.

Did you complete the replacement?

Perform the following procedure in order to verify the repair:

Select DTC.
Select Clear Info.
Operate the vehicle at a speed greater than 3 km/h (2 mph) for 3 seconds.
Select Specific DTC. Enter DTC P0502.

Has the test run and passed?

System OK

Go to Step 1

DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input 3.4L

Automatic Transmission Components
Automatic Transmission Controls Schematics LA1
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

When the PCM detects a low output speed and the vehicle has a large engine speed in a drive gear, then DTC P0502 sets. DTC P0502 is a type B DTC.

Conditions for Running the DTC

•	No TP DTCs P0121, P0122, or P0123.

•	No AT ISS DTCs P0716 or P0717.

•	No engine torque DTC P1644.

•	No TFP manual valve position switch DTC P1810.

•	The transmission is in a drive range.

•	The TP angle is greater than 12%.

•	The input speed is greater than 1500 RPM.

•	The engine torque is greater than 34 N·m (25 lb ft).

Conditions for Setting the DTC

The output speed is less than 150 RPM 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 shift adapts from being updated.

•	The PCM calculates output speed from input speed, engine speed, and commanded gear.

•	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 fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids

•	Inspect the connectors at the PCM, the AT OSS and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

•	Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Wiring Systems.

•	Inspect for a damaged AT OSS. Inspect for damaged transmission rotor teeth.

•	A slipping forward clutch could set DTC P0502.

Test Description

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

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

This step tests the AT OSS circuit for correct resistance.

DTC P0502 Output Speed Sensor Circuit -- Low Input

Step

Action

Value(s)

Yes

Did you perform the Powertrain Diagnostic System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

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

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

Raise and support the drive wheels.
Start and idle the engine.
Place the transmission in DRIVE.
Select Transmission OSS on the Scan Tool .

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

Go to Diagnostic Aids

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 PCM terminals C1-64 and C1-65.
Select AC volts on the J 39200 DMM.
Turn ON the ignition, with the engine OFF.
Rotate the right front drive wheel by hand.
Observe the J 39200 DMM display.

Can a voltage greater than the specified value be obtained?

0.5 V AC

Go to Step 14

Go to Step 4

Leave the J 39200 DMM test leads connected.
Measure circuit resistance.

Is the circuit resistance within the specified range?

1530-1870 ohms

Go to Step 8

Go to Step 5

Is the circuit resistance greater than the specified value?

1870 ohms

Go to Step 11

Go to Step 6

Leave the J 39200 DMM test leads connected.
Disconnect the AT OSS connector at the transmission.

Is the circuit resistance less than the specified value?

1530 ohms

Go to Step 7

Test the signal circuit (CKT 400) and the ground circuit (CKT 401) of the AT OSS for being shorted together.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Test the signal circuit (CKT 400) of the AT OSS for a short to ground.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 9

Reconnect PCM connector C1.
Select DC volts on the J 39200 DMM.
Using the J 35616 , connect the J 39200 DMM test leads to terminals A and B of the AT OSS wiring harness connector end.
Turn ON the ignition, with the engine OFF.

Does the DMM display system voltage?

Go to Step 10

Go to Step 12

Test the signal circuit (CKT 400) of the AT OSS for a short to voltage.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Test the signal circuit (CKT 400) of the AT OSS for an open.
Test the ground circuit (CKT 401) of the AT OSS for an open.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

Remove the AT OSS.

Inspect the AT OSS and the transmission for the following conditions:

•	Incorrect AT OSS

•	AT OSS damage

•	Excessive AT OSS to speed sensor rotor gap

•	Incorrect speed sensor rotor alignment

•	Speed sensor rotor damage

Repair any of the above conditions as necessary.

Refer to Transmission Overhaul in the 4T40-E/4T45-E section of the Transmission Unit Repair Manual.

Did you complete the repair?

Replace the AT OSS.

Did you complete the replacement?

Replace the PCM.

Refer to Powertrain Control Module Replacement/Programming in Engine Controls.

Did you complete the replacement?