For 1990-2009 cars
Engine Controls Components
Power, Ground, VSS, and MIL
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The ignition key contains a transponder that transmits a signal to the theft deterrent module when the ignition switch is turned to the ON position. The theft deterrent module compares the signal from the key and determines if an authorized key is being used. During this period, the engine control module (ECM) turns on the malfunction indicator lamp (MIL) by grounding the control circuit. The MIL control circuit is monitored by the theft deterrent module. When the theft deterrent module senses the voltage change from the ECM grounding the MIL control circuit, the theft deterrent module switches the signal on the VSS/theft deterrent signal circuit from the speed signal to send the frequency code to the ECM. The theft deterrent module sends the frequency code to the ECM on the same circuit used to transmit vehicle speed information to the ECM. The ECM compares the frequency code with the learned frequency code. If the frequency code sent by the theft deterrent module matches the frequency code programmed in the ECM, the ECM allows the engine to start. If the codes do not match, the ECM disables the injectors to prevent the engine from starting.

### Conditions for Running the DTC

The engine is cranking.

### Conditions for Setting the DTC

The ECM has not received the frequency code from the theft deterrent module.

### Action Taken When the DTC Sets

The ECM will not illuminate the malfunction indicator lamp (MIL).

The engine will not start or may start and stall.

### Conditions for Clearing the MIL/DTC

• | The DTC clears after forty consecutive warm-up cycles if no failures report by this diagnostic or any other non-emission related diagnostic.

• | The scan tool clears the MIL/DTC.

### Diagnostic Aids

Use the J 35616 connector test adapter kit for any test that requires probing the ECM harness connector or a component harness connector.

Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems for the intermittents.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. The theft deterrent module will diagnose an open, short to ground or a short to voltage on the VSS/theft deterrent signal circuit. Any faults on this circuit will set a DTC P1502 in the ECM. An inoperative theft deterrent module will also set a P1502. Refer to the diagnostic procedures in Theft Deterrent in order to diagnose these conditions.

#### DTC P1502 - Theft Deterrent System - No Password Received

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Perform Diagnostic System Check - Theft Deterrent in Theft Deterrent.
2. Repair any DTCs or concerns that may prevent the theft deterrent module from providing a frequency code to the ECM.

Did you find and repair a concern with the theft deterrent module or system?

--

Go to Step 5

Go to Step 3

3 | Check for a poor connection or poor terminal tension at the ECM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the problem? | -- | Go to Step 5 | Go to Step 4
4 | Important: This vehicle is equipped with a theft deterrent system that interfaces with the ECM. Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle. Replace the ECM. Refer to Engine Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 5

--

5 |

1. Use the scan tool in order to clear the DTCs.
2. Select DTC and the Specific DTC function.
3. Enter the DTC number that was set.
4. Attempt to start the engine.

Does the scan tool indicate that the diagnostic Passed?

--

Go to Step 6

Go to Step 2

6 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to applicable DTC table | System OK