GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2002 🢒 Eldorado 🢒 Body and Accessories 🢒 Instrument Panel, Gages, and Console 🢒 DTC B2781

Circuit Description

The instrument panel cluster (IPC) supplies a 5 volt signal and a ground circuit for the PASS-Key® system. This allows the IPC to detect PASS-Key® resistance values. Inserting the PASS-Key® ,with resistor pellet, in the ignition lock cylinder completes the PASS-Key® circuit. Contacts in the ignition lock cylinder mate with the pellet contacts. The IPC compares the resistance value of the key pellet to the valid resistance programmed into the IPC. If the proper resistance value is read, the IPC allows the engine to start. If the resistance value is incorrect, a malfunction is present and a DTC will set.

Conditions for Setting the DTC
    • The IPC determines that one of the 15 valid key pellets was detected and matches the resistance of the one stored in the IPCs memory.
    • The IPC class 2 vehicle security password report message was sent and acknowledged by the PCM.
    • The IPC then determines that one of the 15 valid key pellets was detected, but now the key pellet does not match the resistance of the one stored in the IPCs memory.

Action Taken When the DTC Sets

The IPC displays the THEFT SYSTEM PROBLEM, CAR MAY NOT RESTART message on the driver message center.

Conditions for Clearing the DTC
    • This DTC requires an ignition cycle in order to change from current to history.
    • The IPC detects a valid PASS-Key® resistance value on the PASS-Key® signal circuit.
    • A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
    • Use a scan tool.

Diagnostic Aids

Before attempting to diagnose a wiring problem, try to start the vehicle with every available ignition key for the vehicle. If one key starts the vehicle and another key does not, replace the malfunctioning key with another key of the same code value as the key that starts the vehicle.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This test determines the key resistance code currently stored in the IPC memory.

Step

Action

Yes

No

1

Did you perform A Diagnostic System Check-Theft Deterrent?

Go to Step 2

Go to Diagnostic System Check - Theft Deterrent

2
  1. Install a scan tool.
  2. Turn ON the ignition with the engine OFF.
  3. Select the Display DTCs function for the IPC.

Does the scan tool display DTC B2781 as a current DTC?

Go to Step 3

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

3

Does the scan tool display DTC B2710 or B2711 as a current DTC?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 4

4

Inspect the ignition key for dirt or obvious damage.

Does the ignition key appear dirty or damaged?

Go to Step 11

Go to Step 5

5

  1. Turn off the ignition.
  2. Disconnect the steering column lock cylinder connector. (Note which half of the connector is the vehicle harness side and which half of the connector is the steering column harness side.
  3. Back out the terminals for the key resistor input circuit and key resistor reference ground circuit from the vehicle harness side of the connector.
  4. Reconnect the steering column lock cylinder.
  5. Connect a J 35628-A Vats/Passkey Interrogator using terminal adapters from a J 35616 to the key resistor input circuit and key resistor reference ground circuit.
  6. Note: This step may take as long as 45 minutes due to a trial and error process. Turn the rotary switch on the J 35628-A to each code number (1-15) and attempt to start the vehicle with each code number. After each failed starting attempt, you must wait 3 minutes before the next attempt.

Does the vehicle start with one of the codes selected on the J 35628-A?

Go to Step 6

Go to Step 7

6
  1. Note the code number on the J 35628-A that successfully started the vehicle.
  2. Obtain and cut a new ignition key with the correct key code value.
  3. Attempt to start the vehicle with the new ignition key.

Does the vehicle start?

Go to Step 14

Go to Step 8

7

Test the following circuits in the vehicle harness portion for an open or a short:

    • The key resistor input circuit
    • The key resistor reference ground circuit

Was a condition found and corrected?

Go to Step 14

Go to Step 10

8

Test the following circuits in the steering column harness portion for an open or a short:

    • The key resistor input circuit
    • The key resistor reference ground circuit

Was a condition found and corrected?

Go to Step 14

Go to Step 9

9

Inspect for poor connections at the harness connector of the ignition lock cylinder. 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 14

Go to Step 12

10

Inspect for poor connections at the harness connector of the instrument cluster. 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 14

Go to Step 13

11

Clean or replace the ignition key as necessary. Refer to Replacing Keys .

Did you complete the procedure?

Go to Step 14

--

12

Replace the ignition lock cylinder. Refer to Steering Column Lock and Ignition Switch Cylinder Replacement - On Vehicle in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 14

--

13

Replace the instrument cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console.

Did you complete the repair?

Go to Step 14

--

14
  1. Use the scan tool in order to clear the DTCs.
  2. Attempt to start the vehicle.

Does the DTC reset?

Go to Step 2

System OK