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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Chevy K Silverado - 4WD 🢒 Engine 🢒 Engine Controls - 6.6L (LB7) 🢒 DTC P0651

Circuit Description

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

    • The boost sensor
    • The accelerator pedal position (APP) sensor 2
    • The exhaust gas recirculation (EGR) vacuum sensor, if applicable.
    • The barometric pressure (BARO) sensor.
    • The air conditioning (A/C) refrigerant 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 5-volt reference circuits. The ECM monitors the voltage on the 5-volt reference circuit. If the ECM detects that the voltage is out of tolerance, DTC P0651 sets.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC
    • The ECM detects a voltage out of tolerance condition on the 5-volt reference 2 circuit.
    • The above condition is present for longer than 10 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the 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.

Test Description

The number below refers to the step number on the diagnostic table.

  1. If the circuit is shorted to the transmission control module (TCM) MIL request circuit, the scan tool will show skewed BARO and BOOST sensor readings just after the ignition is turned ON. The sensor readings will then return to normal in under 1 second.

DTC P0651

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step  2

Go to Diagnostic System Check - Engine Controls

2
  1. Observe the Freeze Frame/Failure Records data 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.

Does the DTC fail this ignition?

--

Go to Step 3

Go to Intermittent Conditions

3
  1. Turn OFF the ignition.
  2. Disconnect the BARO sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Using a DMM, measure voltage between the 5-volt reference circuit of the BARO sensor and a good ground.

Is the voltage within the specified range?

4.8 - 5.2 V

Go to Step 5

Go to Step 4

4

Does the voltage measure more than the specified value?

5.2 V

Go to Step 8

Go to Step 6

5
  1. Reconnect BARO sensor.
  2. Disconnect the APP sensor.
  3. Using a DMM, measure voltage between the 5-volt reference circuit of APP sensor 2 and the engine ground.

Is the voltage within the specified range?

4.8 - 5.2 V

Go to Intermittent Conditions

Go to Step 9

6
  1. Monitor DMM while disconnecting all other devices connected to the 5-volt reference circuit, one at a time. Refer to Engine Controls Component Views .
  2. If voltage changes when one of the devices are disconnected, replace the component. Refer to the appropriate replacement procedure below:
    3. • The APP sensor
    • The boost sensor
    • Refer to Boost Sensor Replacement .
    • The EGR vacuum sensor, if applicable
    • The air conditioning (A/C) refrigerant pressure sensor

Was a component replaced?

 

Go to Step 11

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Test the 5-volt reference circuit for the following conditions. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
    4. • A short to ground
    • A short to any low reference circuit
    • A short to the fuel pressure regulator control circuit
    • A short to the TCM MIL request circuit
    • A short to the PCM MIL request circuit
    • A short to the ignition 1 relay control circuit

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

8

Test the following circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

    • The 5-volt reference circuit
    • The boost sensor signal circuit
    • The BARO sensor signal circuit
    • The A/C refrigerant pressure sensor signal circuit
    • The EGR vacuum sensor signal circuit, if applicable
    • The APP sensor signal circuit

Did you find and correct the condition?

--

Go to Step 11

Go to Step 10

9

Replace the BARO sensor. Refer to Barometric Pressure Sensor Replacement .

Did you complete the replacement?

--

Go to Step 11

--

10

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 11

--

11
  1. Use a scan tool to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 12

Go to Step 2

12

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK