GM Service Manual Online
For 1990-2009 cars only

Refer to Theft Deterrent System Schematics for a wiring diagram.

Circuit Description

The Vehicle Theft Deterrent module produces the Theft Deterrent Fuel Enable signal when the ignition is ON and the proper key resistor pellet is sensed by the Vehicle Theft Deterrent module. The PCM monitors the Fuel Enable signal during crank. If the proper signal is present on the Theft Deterrent Fuel Enable circuit, the PCM enables fuel delivery to allow the engine to start. If the PCM detects that the fuel enable signal is not present or incorrect while the engine is running, DTC P1626 will be set. The engine will continue to start and run as long as DTC P1626 is stored and the malfunction condition affects only the Theft Deterrent Fuel enable circuit. If the problem affects inputs to the Vehicle Theft Deterrent module, the starter motor may be disabled. If this condition is present, refer to Diagnostic System Check - Theft Deterrent for further diagnosis.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

    • The PCM detects an incorrect signal on the Theft Deterrent Fuel Enable Circuit.
    • The above conditions are present for longer than 2 seconds.

Action Taken When the DTC Sets

The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

Conditions for Clearing the MIL/DTC

    • The DTC becomes history when the conditions for setting the DTC are no longer present.
    • The history DTC clears after 40 malfunction free warm-up cycles.
    • The PCM receives a clear code command from the scan tool.

Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following conditions:

    • Poor connection. Inspect the PCM and VTD module harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the VTD module, turn the ignition ON and observe a DMM connected to the theft deterrent fuel enable circuit at the VTD module harness connector while moving connectors and wiring harnesses related to the vehicle theft deterrent system. A change in voltage will indicate the location of the malfunction.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

DTC P1626 - Theft Deterrent System Fuel Enable Circuit

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: If a loss of DLC data has already been diagnosed using the DLC Diagnosis table, clear this DTC and continue diagnosis with Powertrain On Board Diagnostic (OBD) System Check .

Attempt to select Vehicle Theft Deterrent (VTD) system data with the scan tool.

Can Vehicle Theft Deterrent system data be displayed?

--

Go to Step 3

Go to Step 5

3

  1. Turn OFF the ignition.
  2. Disconnect the PCM and the VTD module.
  3. Check the serial data circuit for an open between the VTD module and the PCM. Refer to

    Cell 50: Class 2 Serial Data Line


    Object Number: 324420  Size: FS
    Data Link Communications Components
    Data Link Communications Description
    Cell 50: Power, Ground and E&C Serial Data Line
    Handling ESD Sensitive Parts Notice
    SIR Caution
    Cell 50: Power, Ground and E&C Serial Data Line
    .
  4. If a problem is found, repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 6

Go to Step 4

4

  1. Check the serial data circuit for poor connections at the PCM.
  2. If a problem is found, repair as necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs .

Was a problem found?

--

Go to Step 6

 

5

  1. Check the serial data circuit for poor connections at the VTD module.
  2. If a problem is found, repair as necessary. Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs .

Was a problem found?

--

Go to Step 6

Go to Diagnostic System Check - Theft Deterrent

6

  1. Review and record scan tool Fail Records data.
  2. Clear DTC P1626.
  3. Attempt to start the vehicle.

Does the vehicle start and continue to run?

--

Go to Step 2

System OK