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For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1997 🢒 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 (TDM) receives and recognizes the transponder code signal from the key, the module internally switches from the speed signal circuit and sends the imo signal to the ECM from terminal 7. The ECM receives the imo signal at terminal 79.

Conditions for Setting the DTC
  1. The TDM did not receive the request signal from the ECM after the ignition was switched On.
  2. A short to ground or voltage in the imo request circuit.
  3. An open in the imo request circuit.
  4. All 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.
    • A history DTC will clear after 20 consecutive ignition cycles if the condition for the fault is no longer present.
    • 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.
    • 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 displays and indicates whether the Theft Deterrent Module (TDM) has received a request signal from the Engine Control Module (ECM).

    2.

  2. If the DTC continues to reset and the circuits are OK, the possibility exists that either the TDM or the ECM may be at fault. The only way to determine which one is by trail and error. Replace the TDM first.

    3.

  3. After determining that the TDM is OK, replace the ECM.

DTC 17 No Engine Request Received

Step

Action

Value(s)

Yes

No

1

Was the Theft Deterrent System Check performed?

--

Go to Step 2

Go to Theft Deterrent System Check

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 from the data list.

Does the scan tool display the parameter 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 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 Theft Deterrent System Check

--

5

Check for a possible intermittent malfunction. Refer to Intermittent and Poor Connections.

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 Theft Deterrent System Check

--

7
    • Reassemble connectors/components removed in previous steps.
    • Install the scan tool and clear codes.
    • Recheck for a current DTC 17 and/or 18.

Is a current DTC 17 or 18 present?

--

Go to Step 8

Go to Theft Deterrent System Check

8

  1. Check all power and ground circuits.
  2. Check the connections at the Theft Deterrent Module.
  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 9

--

9
  1. Reconnect 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 Theft Deterrent System Check

Go to Step 10

10

  1. Remove the previously installed theft deterrent module.
  2. Replace the ECM. Refer to Engine Controls.
  3. Reconnect 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?

--

Go to Theft Deterrent System Check

--