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).
When the ignition switch is turned to the ON position, a signal (transponder code) from the key is transmitted to the Theft Deterrent Module (TDM). During this period the ECM transmits a signal to the TDM requesting the frequency code (imo signal). The TDM compares the signal from the key and decides if an authorized key is being used. After verification, the TDM internally switches from the speed signal circuit and sends the imo signal to the ECM.
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 15 indicates that a short to ground or an open exists in the speed/imo signal circuit (PA14/PA79.)
- The above conditions must be fulfilled for at least 0.51 seconds.
Action Taken When the DTC Sets
| • | The engine starts then stalls. |
| • | The Theft Deterrent Module stores a DTC 15 in memory. |
Conditions for Clearing the DTC
| • | The 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. |
| • | 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. |
| • | If the DTC is an intermittent or history 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 step checks if the Theft Deterrent Module transmitted the immobilizer signal.
-
This step checks for an open circuit between the modules.
-
The module may be faulty if no trouble is found in the power or ground circuits, or if no trouble is found with the connection at the Theft Deterrent Module.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Theft Deterrent System Check performed? | -- | Go to Theft Deterrent System Check | |||||||
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 possible intermittent malfunctions. Refer to Diagnostic Aids. Was 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? | -- | Go to Theft Deterrent System Check | -- | ||||||
7 |
Is the repair complete? | -- | Go to Theft Deterrent System Check | -- | ||||||
8 |
Is a current DTC 15 present? | -- | Go to Theft Deterrent System Check | |||||||
9 | Locate and repair the intermittent malfunction. Is the repair complete? | -- | Go to Theft Deterrent System Check | -- | ||||||
Is the replacement complete and is the reprogramming complete? | -- | Go to Theft Deterrent System Check | -- |
