Hummer H1 (2006+). Manual - part 90

OBD-204

On-Board Diagnostics

_____________________________________________

DTC P0642 5 Volt Reference 1 Circuit Low Voltage (Figure OBD-56)

Figure OBD-56:   5 Volt Refernce 1 Circuit

The Engine Control Module (ECM) Provides 5 volts To The Following Sensors:

• The oil pressure sensor 

• The exhaust gas recirculation (EGR) valve 

• The accelerator pedal position (APP) 1 sensor 

• The rail pressure sensor 

These 5-volt reference circuits are independent of each other outside the ECM, but are bussed together inside the ECM. Therefore,
a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The ECM monitors
the voltage on the 5-volt reference circuit. If the ECM detects a low voltage condition, DTC P0642 sets.

Conditions for Setting the DTC 

• The ECM detects the 5-volt reference 1 circuit voltage is less than 4.7 volts. 

• The above condition is present for 2 seconds. 

Action Taken When the DTC Sets 

• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. 

• The control module records the operating conditions at the time the diagnostic fails. The control module stores this informa-

tion in the Freeze Frame/Failure Records. 

Conditions for Clearing the MIL/DTC 

• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic 

runs and does not fail. 

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes. 

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related 

diagnostic.

• Clear the MIL and the DTC with a scan tool. 

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 On-Board Diagnostics  OBD-205

5745804

Step

Action

Value(s)

Yes

No

    1

NOTE: Before clearing DTC(s) use the scan tool “Capture info”
to record Freeze Frame and Failure Records for reference, as data
will be lost when “Clear Info” function is used 

Was the “On-Board Diagnostic (OBD) System Check” per-
formed?

Go to step 2.

Go to OBD Sys-

tem Check.

    2

1.

Observe the Freeze Frame/Failure Records for this DTC.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Operate the vehicle within the Conditions for Running the 
DTC. You may also operate the vehicle within the conditions 
that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 3

Go to Intermit-

tent Conditions 

    3

1.

Turn OFF the ignition.

2.

Disconnect the accelerator pedal position (APP) sensor.

3.

Turn ON the ignition, with engine OFF.

4.

Measure the voltage from the 5-volt reference circuit 717 
(TN) of the APP 1 sensor to a good ground with a DVOM.

Is the voltage within the specified range?

4.7-5.2

Volts

Go to Step 7 

Go to Step 4 

    4

1.

Observe the DVOM while disconnecting all other compo-
nents connected to the 5-volt reference, one at a time.

2.

If voltage changes when one of the above components are 
disconnected, replace the component. 

• Engine Oil Pressure Sensor and/or Switch Replacement 

• Exhaust Gas Recirculation (EGR) Valve Replacement 

• Fuel Rail Pressure (FRP) Sensor Replacement

Was a component replaced?

Go to Step 8 

Go to Step 5 

    5

Test each 5-volt reference 1 circuits 508 (TN), 717 (TN), 617
(GY), and 106 (GY) for a short to ground. 

Did you find and correct the condition?

Go to Step 8 

Go to Step 6 

    6

Replace the faulty ECM. 

Did you complete the replacement?

Go to Step 8 

    7

Replace the faulty APP sensor. 

Did you complete the replacement?

Go to Step 8 

    8

1.

Clear the DTCs with a scan tool.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Operate the vehicle within the Conditions for Running the 
DTC. You may also operate the vehicle within the conditions 
that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 1 

Go to Step 9

   9

Using the Scan Tool select “Capture Info,” Review Info.” Are
any DTC’s displayed that have not been diagnosed?

Go to the appli-

cable DTC 

table.

System OK.

OBD-206

On-Board Diagnostics

_____________________________________________

DTC P0643 5 Volt Reference 1 Circuit High Voltage (Figure OBD-57)

Figure OBD-57:   5 Volt Reference 1 Circuit

Circuit Description

The engine control module (ECM) provides 5 volts to the following sensors:

• The oil pressure sensor 

• The exhaust gas recirculation (EGR) valve 

• The accelerator pedal position (APP) 1 sensor 

• The rail pressure sensor 

These 5-volt reference circuits are independent of each other outside the ECM, but are bussed together inside the ECM. Therefore,
a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The ECM monitors
the voltage on the 5-volt reference circuit. If the ECM detects a high voltage condition, DTC P0643 sets.

Conditions for Setting the DTC 

• The ECM detects the 5-volt reference 1 circuit voltage is more than 5.2 volts. 

• The above condition is present for longer than 2 seconds. 

Action Taken When the DTC Sets 

• The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. 

• The control module records the operating conditions at the time the diagnostic fails. The control module stores this informa-

tion in the Freeze Frame/Failure Records. 

Conditions for Clearing the MIL/DTC 

• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic 

runs and does not fail. 

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes. 

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related 

diagnostic.

• Clear the MIL and the DTC with a scan tool. 

_____________________________________________

 On-Board Diagnostics  OBD-207

5745804

Step

Action

Value(s)

Yes

No

    1

NOTE: Before clearing DTC(s) use the scan tool “Capture info”
to record Freeze Frame and Failure Records for reference, as data
will be lost when “Clear Info” function is used 

Was the “On-Board Diagnostic (OBD) System Check” per-
formed?

Go to step 2.

Go to OBD Sys-

tem Check.

    2

1.

Turn ON the ignition, with the engine OFF.

2.

Observe the 5-Volt Reference 1 parameter with a scan tool.

Is the 5-Volt Reference 1 parameter more than the specified
value?

5.2 Volts

Go to Step 3 

Go to Intermit-

tent Conditions

    3

Test each 5-volt reference 1 circuits 508 (TN), 717 (TN), 617
(GY), 106 (GY) for a short to voltage. 

Did you find and correct the condition?

Go to Step 6 

Go to Step 4 

    4

Replace the faulty ECM. 

Did you complete the replacement?

Go to Step 8 

    5

1.

Clear the DTCs with a scan tool.

2.

Turn OFF the ignition for 30 seconds.

3.

Start the engine.

4.

Operate the vehicle within the Conditions for Running the 
DTC. You may also operate the vehicle within the conditions 
that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 1 

Go to Step 6

   6

Using the Scan Tool select “Capture Info,” Review Info.” Are
any DTC’s displayed that have not been diagnosed?

Go to the appli-

cable DTC 

table.

System OK.