For 1990-2009 cars

### Circuit Description

Modules that are connected to the shared communication circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have pre-recorded information about what messages are needed to be exchanged on the serial data circuits for each virtual network. The messages are usually supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1626 Lost Communication With Theft Deterrent Control Module

### Conditions for Running the DTCs

• | The ignition is ON and the engine is cranking.

• | The DTC P1626 diagnostic runs once per drive cycle.

### Conditions for Setting the DTC

The engine control module (ECM) cannot communicate with the theft deterrent control module

### Action Taken When the DTC Sets

• | The DTC P1626 is stored in the ECM.

• | Engine control system functions are disabled and the engine will not start.

### Conditions for Clearing the DTC

• | A current DTC clears when the malfunction is no longer present.

• | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

• | The scan tool can clear the DTC from the module memory.

### Diagnostic Aids

• | An open or a short in the serial data circuits of the theft deterrent control module can cause a DTC P1626 to set. The serial data circuit fault will also cause the following conditions:

- | The theft deterrent status will switch to Enable and the engine will crank but not start.

- | If there is open circuit, the scan tool will not communicate with the ECM, but will continue to communicate with the transmission control module (TCM).

- | If there is a short circuit, the scan tool will not communicate with either the ECM or the TCM.

- | The DTC P1626 will be stored in memory and is displayed by the scan tool when communication with the ECM resumes.

• | An intermittent electrical condition in the theft deterrent system can cause this code to set. Refer to Testing for Intermittent Conditions and Poor Connections .

### Test Description

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

1. This step tests for ignition voltage to the theft deterrent module. The theft deterrent module cannot communicate with the ECM if there is no ignition positive voltage.

2. This step tests for a good ground to the theft deterrent module. The theft deterrent module cannot communicate with the ECM if there is no ground circuit.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Theft Deterrent System Schematics Connector End View Reference: Component Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Is DTC P1626 present? | Go to Step 3 | Go to Diagnostic System Check - Vehicle
3 |

1. Turn OFF the ignition.
2. Disconnect the theft deterrent module electrical connector.
3. Turn the ignition ON, with the engine OFF.
4. Connect a test lamp to the ignition 1 voltage circuit at the connector and ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 6

4 | Connect a test lamp to B+ and the ground circuit of the theft deterrent module. Did the test lamp illuminate? | Go to Step 7 | Go to Step 5
5 | Repair the open or the poor connection in the theft deterrent module ground circuit. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs . Did you find and correct a condition? | Go to Step 10 | Go to Step 7
6 | Repair the open or the poor connection ignition 1 voltage circuit of the theft deterrent module. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs . Did you find and correct a condition? | Go to Step 10 | Go to Step 7
7 | Inspect for a poor electrical connection at the theft deterrent control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct a condition? | Go to Step 10 | Go to Step 8
8 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Attempt to start the engine.
4. Use the scan tool and check for DTCs.

Did the engine start and run with no DTC P1626 set?

Go to Diagnostic Aids

Go to Step 9

9 | Replace the theft deterrent control module. Refer to Control Module References . Did you complete the replacement? | Go to Step 10 | --
10 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Attempt to start and run the engine.
4. Use the scan tool and check for DTCs.

Did DTC P1626 set?

Go to Step 2

System OK