GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2002 🢒 Eldorado 🢒 Transmission/Transaxle 🢒 Shift Lock Control 🢒 DTC B2502

Circuit Description

With the ignition ON, ignition 1 voltage is supplied to the coil side feed of the PARK relay. The control circuit of the PARK relay is controlled by the body control module (PZM). When the PZM receives a class 2 serial data message from the powertrain control module (PCM) stating that the automatic transmission is in the PARK position the PZM grounds the control circuit of the PARK relay via an internal switch called a driver. The driver supplies a path to ground for the component being controlled. Each driver has a fault line which the PZM monitors. When the PZM commands the PARK relay OFF, the voltage of the control circuit should be high, near battery voltage. If the circuit voltage is measured below the fault line the DTC is set.

Conditions for Running the DTC

Ignition in the ON position.

Conditions for Setting the DTC

The PZM determines that the PARK relay control circuit is shorted to battery voltage.

Action Taken When the DTC Sets

The PZM will continue commanding the requested state until the state is achieved or until the request changes.

Conditions for Clearing the DTC

The PZM determines that the PARK relay control circuit is no longer shorted to battery voltage.

Test Description

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

  1. Listen for an audible click when the PARK relay operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. Tests for voltage at the coil side of the Park relay. The CRUISE fuse supplies power to the coil side of the PARK relay.

    3.

  3. Verifies that the PZM is providing ground to the PARK relay.

    4.

  4. Tests if ground is constantly being applied to the PARK relay.

    5.

  5. Test if the control circuit of the PARK relay is shorted.

Step

Action

Yes

No

Schematic Reference: Shift Lock Control Schematics

1

Did you perform the Automatic Transmission Shift Lock Control Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Automatic Transmission Shift Lock Control

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the PARK relay ON and OFF.

Does the PARK relay turn ON and OFF with each command?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the PARK relay.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the ignition 1 voltage circuit of the PARK relay with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  1. Connect a test lamp between the control circuit of the PARK relay and the ignition 1 voltage circuit of the PARK relay.
  2. With a scan tool, command the PARK relay ON and OFF .

Does the test lamp turn ON and OFF with each command?

Go to Step 8

Go to Step 5

5

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 6

6

Test the control circuit of the PARK relay for a short to battery voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test the control circuit of the PARK relay 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 13

Go to Step 9

8

Inspect for poor connections at the PARK relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

9

Inspect for poor connections at the harness connector of the body control module (PZM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Repair the open in the ignition 1 voltage circuit of the PARK relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

11

Replace the PARK relay. Refer to Wiring Repairs in Wiring Systems.

Did you complete the replacement?

Go to Step 13

--

12

Replace the body control module (PZM). Refer to Body Control Module Replacement in Body Control System.

Did you complete the replacement?

Go to Step 13

--

13
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK