GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2008 🢒 Vibe - FWD 🢒 DTC 🢒 DTC B2784

Circuit Description

The transponder key coil is built into the transponder key amplifier and receives a key code signal from the transponder chip in the key. This signal is amplified by the amplifier, then it is sent to the transponder key ECU assembly. monitors the status of the unlock warning switch. The transponder key ECU assembly detects when the unlock warning switch is ON. If the transponder key ECU assembly does not detect the key code signal, DTC B2784 will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2784 Antenna Coil Open / Short

Conditions for Running the DTC

This DTC shall run when key is inserted into key cylinder.

Conditions for Setting the DTC

The antenna coil is open or shorted to ground.

Action Taken When the DTC Sets

The engine will not start.

Conditions for Clearing the DTC

The DTC will clear when conditions for setting the DTC have been repaired.

Step

Action

Value(s)

Yes

No

Schematic Reference: Immobilizer Schematics

Connector End View Reference: Immobilizer Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, observe the Antenna 1 Status parameter in the Immobilizer data list.

Does the Antenna 1 Status parameter display Normal?

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Go to Step 3

Go to Step 8

3

  1. Turn OFF ignition.
  2. Disconnect the transponder key amplifier harness connector and the transponder key ECU assembly harness connector.
  3. Measure the resistance between the transponder key ECU assembly terminals and the transponder key amplifier terminals as follows:
    4. • ECU terminal 4 to amplifier terminal 5
    • ECU terminal 5 to amplifier terminal 7
    • ECU terminal 14 to amplifier terminal 1
    • ECU terminal 15 to amplifier terminal 4
  4. Measure the resistance between the transponder key ECU assembly terminals and ground as follows:
    5. • ECU terminal 4 to ground
    • ECU terminal 5 to ground
    • ECU terminal 14 to ground
    • ECU terminal 15 to ground

Is the resistance measured less than or greater than the specified values?

ECU to amplifier Less = 1 Ohm

ECU to ground = 10 Kohms or greater

Go to Step 4

Go to Step 5

4
  1. Reconnect the transponder key amplifier harness connector and the transponder key ECU assembly harness connector.
  2. Measure the voltage between the transponder key ECU assembly terminal 14 and the body ground with no key in the ignition and then with the key in the ignition.
  3. Measure the resistance between the transponder key ECU assembly terminal 5 and body ground.

Is the voltage and resistance measured less than or greater than the specified values?

No key in ignition = below 1 volt and with key in ignition = 4.6 - 5.4 volts

ECU to body ground = less than 1 ohm

Go to Step 7

Go to Step 6

5

Test the applicable circuit for an open/high resistance or short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 9

Go to Step 7

6

Inspect for poor connections at the harness connector of the transponder key amplifier. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition?

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Go to Step 9

Go to Step 8

7

Replace the transponder key amplifier.

Did you complete the replacement?

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Go to Step 9

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8

Replace the transponder key ECU assembly.

Did you complete the replacement?

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Go to Step 9

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9
  1. Use the scan tool in order to clear the DTC.
  2. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

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Go to Step 2

System OK