GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Eldorado 🢒 DTC 🢒 DTC P0503

Object Number: 654440 Size: SF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

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 PCM. The PCM converts the AC voltage into a digital signal. The PCM uses vehicle speed to determine shift timing, torque converter clutch apply and release and gear ratio.

If the PCM detects a loss of vehicle speed while the vehicle is in motion, then DTC P0503 sets. DTC P0503 is a type B DTC.

Conditions for Running the DTC
    • No AT ISS DTCs P0716 or P0717.
    • No IMS DTCs P1820, P1822, P1823, or P1825.
    • No 1-2 shift solenoid valve electrical DTC P1843.
    • The engine run time is greater than 5 seconds.
    • The transmission is not in PARK or NEUTRAL.
    • The time since the gear select lever change is greater than 6 seconds.
    • The transmission input shaft speed has not changed by 500 RPM or greater for at least 4.8 seconds.
    • LD8: The transmission output shaft speed is greater than 1244 RPM and has not increased by 500 RPM or greater for at least 2 seconds.
    • L37: The transmission output shaft speed is greater than 1484 RPM and has not increased by 500 RPM or greater for at least 2 seconds.

Conditions for Setting the DTC
    • LD8: The transmission output shaft speed drops 1089 RPM or greater for at least 1 second.
    • L37: The transmission output shaft speed drops 1299 RPM or greater for at least 1 second.

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 adapt functions.
    • The PCM calculates vehicle speed from the automatic transmission input (shaft) speed sensor 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 P0503 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 1950 ohms which would indicate an open in the high signal circuit, the low signal circuit or the VSS.

DTC P0503 Output Speed Sensor Circuit -- Intermittent

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

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 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

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Disconnect PCM connector C1.
  3. Using the J 35616 connector test adapter kit, connect the J 39200 digital multimeter (DMM) between PCM terminals C1-56 and C1-57.
  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 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

4

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

Is the circuit resistance within the specified range?

1300-1950 ohms

Go to Step 8

Go to Step 5

5

Is the circuit resistance greater than the specified value?

1950 ohms

Go to Step 11

Go to Step 6

6
  1. Leave the J 39200 DMM test leads connected.
  2. Disconnect the VSS connector at the transmission.

Is the circuit resistance less than the specified value?

1300 ohms

Go to Step 7

Go to Step 13

7

Test the high signal circuit (CKT 400) and the low signal circuit (CKT 401) 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 (CKT 400) of the VSS 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 15

Go to Step 9

9

  1. Reconnect PCM connector C1.
  2. Using the J 35616 , connect the J 39200 DMM test leads to terminals A and B of 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 (CKT 400) of the VSS for a short to voltage.

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

--

11
  1. Test the high signal circuit (CKT 400) of the VSS for an open.
  2. Test the low signal circuit (CKT 401) of the VSS for an open.

Refer to Circuit Testing 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 Transmission Overhaul in 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 Powertrain Control Module Replacement in Engine Controls.

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. Road test the vehicle and ensure that the Transmission OSS is greater than 1198 RPM and does not drop 175 RPM or greater for 2 seconds.
  4. Select Specific DTC.
  5. Enter DTC P0503.

Has the test run and passed?

--

System OK

Go to Step 1