Theft Deterrent Diagnostic Circuit
Circuit Description
The Theft Deterrent Module (Immobilizer) uses terminal 7 to send the vehicle speed signal and the frequency code (imo signal) to terminal 79 of the Engine Control Module (ECM).
After the ECM requests the imo signal, the Theft Deterrent Module internally blocks the speed signal and sends the imo signal after the ECM requests the imo signal. Both signals cannot be transmitted at the same time. The ECM compares the received imo signal with the programmed stored signal.
If both codes are the same, the engine control functions (fuel pump drive and injector signals) are released. Non matching codes block the engine functions and the car cannot be started.
Conditions for Setting the DTC
- DTC 16 indicates a short to voltage in the speed/imo signal circuit.
- The above conditions must be fulfilled for at least 0.51 seconds.
Action Taken When the DTC Sets
The engine starts then stalls.
Conditions for Clearing the DTC
| • | The conditions for the fault are no longer present. |
| • | The ignition switch was cycled 20 times. |
| • | The use of the 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 following numbers refer to the step numbers on the diagnostic table:
-
This checks if the Theft Deterrent Module transmits the immobilizer signal.
-
Include turning the key to the On position when checking for a short to B+.
-
The module may be faulty if no trouble is found in the power circuits, if no trouble is found in the ground circuits, or if no trouble if found in the connection at the Theft Deterrent Module. However, this is an extremely unlikely failure.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Immobilizer System Check performed? | -- | ||
Does the scan tool display TRANSMITTED? | -- | |||
Is the measured resistance within the specified value? | Less than 5 ohms | |||
4 | Check the circuits between the Theft Deterrent Module and the ECM for intermittent malfunctions. Refer to Diagnostic Aids. Is a problem found? | -- | ||
5 | Use the DMM to measure the resistance from terminal 7 to a known good ground. Is the measured resistance within the specified value? | OL | ||
6 |
Is the repair complete? | -- | -- | |
7 |
Are the measured voltages within the specified value? | Less than 0.1 V | ||
8 |
Is the repair complete? | -- | -- | |
9 |
Is the repair complete? | -- | -- | |
10 |
Important: The immobilizer function must be activated if a new BCM is installed. Refer to Programming Engine Control Module.
Was the reprogramming successful? | -- | -- | |
11 |
Is the repair complete? | -- | -- | |
Is the replacement complete and is the reprogramming complete? | -- | -- |
