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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1998 🢒 Catera 🢒 DTC 🢒 DTC 18 MIL Circuit

Theft Deterrent Diagnostic Circuit
Object Number: 243482 Size: LF

Circuit Description

When the ignition switch is turned ON, the Engine Control Module (ECM) sends a signal over the lamp circuit to terminal 2 of the Theft Deterrent Module (Immobilizer) requesting the frequency code (imo signal).

After the Theft Deterrent Module receives and recognizes the signal, the Theft Deterrent Module internally blocks the speed signal output at terminal 7. The Theft Deterrent Module allows the imo signal to be transmitted out at terminal 7. The ECM receives the imo signal at terminal 79.

Conditions for Setting the DTC
  1. The request signal from the ECM was not received after the ignition was switched on.
  2. A short to ground in the imo signal request circuit between the Gauge Cluster and Theft Deterrent Module.
  3. An open in the imo signal request circuit between the Gauge Cluster and Theft Deterrent Module. The above conditions must be fulfilled for at least 0.51 seconds.

Action Taken When the DTC Sets

The engine will start then stall.

Conditions for Clearing the DTC
    • Conditions for the fault are no longer present.
    • The ignition switch been cycled 20 times.
    • Using a scan tool.

Diagnostic Aids
    • Using a DMM, check the ground circuit at terminal 4. Typical voltage drop readings are 100mV or less. When measuring the resistance it should measure at close to 0 (zero) ohms.
    • Use Terminal Repair Kit J 38125-A or J 35616-A to gauge all terminal contacts. Check for damaged connectors and poor wire to terminal connections. Refer to 8A-4-5 for procedure.
    • If the DTC is an intermittent DTC, try performing the tests shown while "wiggling" wiring and connectors, this can often cause the malfunction to appear.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. The scan tool indicates and displays whether the theft deterrent module has received a request signal from the EBTCM.

    2.

  2. If no trouble is found in the power and ground circuits or the connection at the theft deterrent module, the module may be faulty. However, this is an extremely unlikely failure.

    3.

  3. The possibility exists that either the theft deterrent module or the ECM might be at fault. In order to determine which one, replace the theft deterrent module first.

    4.

  4. After determing that the theft deterrent module is OK, replace the ECM.

DTC 18 MIL Circuit

Step

Action

Value(s)

Yes

No

1

Was the Immobilizer System Check performed?

--

Go to Step 2

Go to Diagnostic System Check - Theft Deterrent .

2

  1. Install the scan tool.
  2. Select immobilizer on the scan tool.
  3. Turn the ignition switch to the ON position.
  4. Select engine request on the scan tool.

Does the scan tool display RECEIVED?

--

Go to Step 5

Go to Step 3

3
  1. Turn the ignition switch to the OFF position.
  2. Disconnect the theft deterrent module connector.
  3. Turn the ignition switch to the ON position.
  4. Use the DMM to measure the voltage between terminal 2 of the theft deterrent module connector and a known good ground.

Is the measured voltage within the specified value?

B+

Go to Step 7

Go to Step 4

4
  1. Locate an open or a high resistance in circuit XP21.
  2. Repair the open or the high resistance in circuit XP21.

Is the repair complete?

--

Go to Diagnostic System Check - Theft Deterrent .

--

5

Check for intermittent problems. Refer to Diagnostic Aids for each DTC for diagnosis.

Was an intermittent problem found?

--

Go to Step 6

Go to Step 7

6

Locate and repair the intermittent problem.

Is the repair complete?

--

Go to Diagnostic System Check - Theft Deterrent .

--

7

  1. Check all power and ground circuits.
  2. Check the theft deterrent module connector.
  3. Replace the theft deterrent module if these circuits are OK. Refer to Steering Wheel and Column On Vehicle Service.

Is the repair or replacement complete?

--

Go to Step 8

--

8

  1. Connect all connectors and components that were disconnected.
  2. Install the scan tool.
  3. Turn the ignition switch to the ON position.
  4. Select ENGINE REQUEST on the scan tool.

Does the scan tool display RECEIVED?

--

Go to Diagnostic System Check - Theft Deterrent .

Go to Step 9

9

  1. Remove the previously installed theft deterrent module.
  2. Replace the ECM. Refer to Engine Controls.
  3. Connect all connectors and components that were disconnected.
  4. Install the scan tool.
  5. Turn the ignition switch to the ON position.
  6. Select ENGINE REQUEST on the scan tool.

Does the scan tool display RECEIVED?

--

System OK

--