For 1990-2009 cars

#### 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

1. DTC 16 indicates a short to voltage in the speed/imo signal circuit.
2. 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:

1. This checks if the Theft Deterrent Module transmits the immobilizer signal.

2. Include turning the key to the On position when checking for a short to B+.

3. 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.

#### DTC 16 Vehicle Speed Signal (Voltage High)

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. Connect the scan tool to the Data Link Connector (DLC).
2. Turn the ignition switch to the ON position.
3. Select IMMOBILIZER SIGNAL.

Does the scan tool display TRANSMITTED?

--

Go to Step 4

Go to Step 3

3 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the wiring harness connector from the Theft Deterrent Module.
3. Disconnect the connector from the Engine Control Module (ECM).
4. Use the DMM to measure the resistance between terminal 7 of the Theft Deterrent Module connector and terminal 79 of the ECM connector.

Is the measured resistance within the specified value?

Less than 5 ohms

Go to Step 5

Go to Step 6

4 | Check the circuits between the Theft Deterrent Module and the ECM for intermittent malfunctions. Refer to Diagnostic Aids. Is a problem found? | -- | Go to Step 11 | Go to Step 10
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 | Go to Step 7 | Go to Step 8
6 |

1. Locate the open circuit between terminal 7 of the Theft Deterrent Module and pin 79 of the ECM.
2. Repair the open.

Is the repair complete?

--

Go to Diagnostic System Check - Theft Deterrent .

--

7 |

1. Use a DMM to measure the voltage from terminal 7 to a known good ground.
2. Turn the ignition switch to the ON position.
3. Use a DMM to measure the voltage from terminal 7 to a known good ground.

Are the measured voltages within the specified value?

Less than 0.1 V

Go to Step 10

Go to Step 9

8 |

1. Locate a short to ground in the circuit between the Theft Deterrent Module and the ECM.
2. Repair the short to ground.

Is the repair complete?

--

Go to Diagnostic System Check - Theft Deterrent .

--

9 |

1. Locate a short to voltage in the related circuits between the Theft Deterrent Module and the ECM.
2. Repair the short to voltage.

Is the repair complete?

--

Go to Diagnostic System Check - Theft Deterrent .

--

10 | Important: The immobilizer function must be activated if a new BCM is installed. Refer to Programming Engine Control Module.

1. Check the Theft Deterrent Module installation.
2. Reprogram the Theft Deterrent Module if installed properly. Refer to Programming Theft Deterrent Module.

Was the reprogramming successful?

--

Go to Diagnostic System Check - Theft Deterrent .

--

11 |

1. Locate an intermittent malfunction.
2. Repair the intermittent malfunction.

Is the repair complete?

--

Go to Diagnostic System Check - Theft Deterrent .

--

12 |

1. Check the power circuits.
2. Check the ground circuits.
3. Check for poor connections at the Theft Deterrent Module. Refer to Diagnostic Aids.
4. Replace the Theft Deterrent Module. Refer to Steering Wheel and Column On Vehicle Service.
5. Reprogram the Theft Deterrent Module. Refer to Programming Theft Deterrent Module.

Is the replacement complete and is the reprogramming complete?

--

Go to Diagnostic System Check - Theft Deterrent .

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