Hummer H2. Manual - part 174

DTC P1626

Circuit Description

The control module communicates with other modules using the Class 2 Serial Data circuit. The vehicle theft
deterrent (VTD) body control module (BCM) sends a vehicle security password to the powertrain control
module (PCM), via the Class 2 Serial Data circuit, after the BCM has sensed the proper operation of the ignition
switch and lock, and determined that the switch and lock have not been tampered with. If this password matches
the password stored in the PCM, fuel will be enabled. If the BCM does not send a password, or if the PCM does
not receive it, the vehicle will not start, or it may start and stall. This will set a DTC P1626 in the PCM memory.
If communication is lost after receiving the password, the VTD Passlock system will go into Fail Enable, set a
U1192 in the PCM memory, and the engine will continue to run. This will allow the engine to restart on future
ignition cycles but may set a DTC P1626 as the engine is started. If the battery is disconnected or the codes are
cleared, the vehicle will lose its Fail Enable status and will not start until communication is re-established.

Conditions for Running the DTC

The vehicle theft deterrent (VTD) system is enabled.

The fuel enable decision point has been reached, or the engine is cranking.

Conditions for Setting the DTC

The powertrain control module (PCM) has not established communications with the body control module
(BCM) and has not received a valid password before the fuel disable decision point was reached.

Action Taken When the DTC Sets

The powertrain control module (PCM) stores the DTC in history after the first failure but will not
illuminate the malfunction indicator lamp (MIL).

The powertrain control module (PCM) records the operating conditions at the time the diagnostic fails.
The PCM stores the failure information in the scan tools Freeze Frame/Failure Records.

Conditions for Clearing the MIL/DTC

A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles.

A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the start-up coolant
temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle.

Use the scan tool Clear Information function.

3. Momentarily rotate the ignition switch to CRANK.

4. Release the ignition switch to ON.

5. Select the body control module display DTCs

function on the scan tool.

Does the DTC reset?

Go to

Step 3

System OK

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Theft Deterrent - Hummer H2

Diagnostic Aids

Check for published service bulletins relating to exhibited symptoms or component operation.

Inspect all related wiring and connections including the powertrain control module (PCM) and body
control module (BCM) connections. These may cause an intermittent malfunction.

If the Class 2 Serial Data circuit is shorted to ground or shorted to voltage, then all systems connected to
the serial data circuit will not be able to communicate properly. Systems capable of storing loss of
communications DTCs, or the DTCs with the letter "U" as a prefix, will have these codes stored in their
memory. If a DTC U1192 is stored in the PCM memory along with the P1626, then a fault occurred at
some point after the PCM received the correct password. The BCM must also be checked for intermittent
operation due to a loss of power or ground to the module itself. After repairing the cause of DTC 1626,
clear all DTCs from the systems capable of storing this DTC and DTC U1192.

The VTD Passlock parameters can be monitored in the PCM under engine data 2, display with a scan
tool.

The scan tool Diagnostic Circuit Check can be used to:

{

Monitor the Class 2 Serial Data circuit for modules which have been or are communicating.

{

Monitor for loss of communications DTCs with the letter "U" as a prefix: U1001-U1199.

{

Clear loss of communication DTCs. When a Clear Codes command is issued, all codes, Freeze
Frame and Failure Records information is cleared.

The scan tool Class 2 Message Monitor will show the status of each module on the Class 2 circuit. A
status of Active indicates that the module is communicating with the scan tool. An Inactive status
indicates that the module previously communicated with the scan tool, but is not communicating
currently. The inactive status will only appear if the loss of communication occurs while on the Message
Monitor screen. If a module is not listed at all, then the missing module never successfully established
communications with the scan tool or lost communication while on another screen. Refer to Scan Tool
Does Not Communicate with Class 2 Device in Data Link Communications for the complete Class 2
data link to determine if there are any unlisted modules.

An intermittent may be caused by any of the following conditions:

A poor connection

Rubbed through wire insulation

A broken wire inside the insulation

Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for
Intermittent Conditions and Poor Connections in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

IMPORTANT: Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs

will also clear valuable Freeze Frame and Failure Records data.

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Theft Deterrent - Hummer H2

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

2: This test checks if communications can be established between the scan tool and the body control
module (BCM). If the scan tool cannot communicate with the BCM, refer to Diagnostic System Check -
Theft Deterrent in Theft Deterrent.

3: This test checks for any opens in the serial data circuit between the powertrain control module (PCM)
and the BCM. This also checks for any intermittent malfunctions associated with the serial data circuit.

4: This step is to determine if the condition that set the DTC is still present. The engine must be cranked
in order to set this DTC. If the condition is present, the engine will start and then stall, indicating the
PCM is disabling fuel.

7: Use a scan tool to clear and check for any DTCs in all the modules connected to the Class 2 Serial Data
circuit, such as the PCM, BCM, automatic temperature control (ATC), and body control module (BCM).

DTC P1626 Loss of Serial Communication with VTD

Step

Action

Yes

Schematic Reference:Data Link Connector (DLC) Schematics

Did you perform the Vehicle Theft Deterrent
Diagnostic System Check?

Go to Step 2

Go to Diagnostic System
Check - Theft Deterrent

1. Install a scan tool.

2. Momentarily rotate the ignition switch to

CRANK.

3. Release the ignition switch to ON.

4. Select the Powertrain control module display

DTCs function on the scan tool.

Does the scan tool display DTC P1626 as a current
DTC?

IMPORTANT:

You must diagnose the Bxxxx codes prior to
diagnosing any Pxxxx code.

IMPORTANT:

Do not start the vehicle.

Go to Step 3

Go to Testing for

Intermittent Conditions and

Poor Connections in Wiring

Systems

Check the Class 2 Serial Data circuit for the
following intermittent conditions:

An open in the Class 2 Serial Data circuit
between the PCM and the BCM

A short to ground

A short to voltage

Loose or damaged terminals at the DLC,

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Theft Deterrent - Hummer H2

PCM, or the BCM

Did you find a problem?

Go to Step 6

Go to Step 4

1. Turn OFF the ignition.

2. Connect or install any connectors or

components that were disconnected or
removed.

3. Clear all DTCs using a scan tool.

4. Turn OFF the ignition for 15 seconds.

5. Attempt to start the engine.

Does DTC P1626 reset?

Go to Step 8

Go to Step 5

This DTC is intermittent.
Are any additional DTCs stored?

Go to the

applicable

DTC table

Go to Testing for

Intermittent Conditions and

Poor Connections in Wiring

Systems

Repair the circuit as necessary. Refer to Wiring
Repairs or Connector Repairs in Wiring Systems.
Is the action complete?

Go to Step 7

1. Turn OFF the ignition.

2. Connect or install any connectors or

components that were disconnected or
removed.

3. Clear all PCM DTCs using a scan tool.

4. Turn OFF the ignition for 15 seconds.

5. Start the engine and allow it to run.

Does the DTC reset?

IMPORTANT:

Before Clearing DTCs, monitor all DTC status
parameters and note any additional DTCs.

Go to Step 2

System OK

Inspect for poor connections at the BCM. Refer to
Testing for Intermittent Conditions and Poor
Connections and Connector Repairs in Wiring
Systems.
Did you find and correct the condition?

Go to Step 7

Go to Step 9

IMPORTANT:

When replacing the BCM refer to Body Control
Module (BCM) Programming/RPO Configuration
in Body Control System.

2004 Hummer H2

2004 ACCESSORIES & EQUIPMENT Theft Deterrent - Hummer H2

Content .. 172 173 174 175 ..