GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2006 🢒 XLR 🢒 DTC 🢒 DTC P0651

Circuit Description

The engine control module (ECM) provides a 5-volt reference to the following sensors:

    • The throttle position (TP) sensors 1 and 2
    • The accelerator pedal position (APP) sensor 2
    • The fuel level sensor 1
    • The air conditioning (A/C) refrigerant
    • The fuel tank pressure (FTP) sensor
    • The engine oil pressure (EOP) sensor

The ECM monitors voltage on the 5-volt reference circuit. If the ECM detects that the voltage on the 5-volt reference circuit is outside a calibrated range, DTC P0651 will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0651 5-Volt Reference 2 Circuit

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The ECM detects a voltage that is out of range on the 5-volt reference circuit for more than 1 second.

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 information 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.

Test Description

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

  1. This step will determine if the throttle body is at fault, or if another device or circuit condition is at fault.

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 - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

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 Intermittent Conditions

3
  1. Turn OFF the ignition.
  2. Disconnect the throttle body electrical connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Measure the voltage from the 5-volt reference circuit of the throttle position (TP) sensors 1 and 2 of the throttle body harness connector to a good ground with a DMM.

Is the voltage within the specified range?

4.8-5.2 V

Go to Step  5

Go to Step 4

4

Is the voltage more than the specified value?

5.2 V

Go to Step 8

Go to Step 6

5

  1. Connect the throttle body electrical connector.
  2. Disconnect the A/C refrigerant pressure sensor.
  3. Measure the voltage from the 5-volt reference circuit of the A/C refrigerant pressure sensor to a good ground with a DMM.

Is the voltage within the specified range?

4.8-5.2 V

Go to Step 9

Go to Step 10

6
  1. Monitor the DMM while disconnecting all other devices connected to this 5-volt reference circuit one at a time.
  2. If voltage changes when one of the above components are disconnected, replace the component. Refer to the appropriate replacement procedure.

Was a component replaced?

--

Go to Step 12

Go to Step 7

7

Test the 5-volt reference circuit for a short to ground or for a short to any sensor low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 12

Go to Step 9

8
  1. Turn ON the ignition, with the engine OFF.
  2. Test the following circuits for a short to voltage:
    3. • All circuits on this 5-volt reference circuit
    • The fuel tank pressure (FTP) sensor signal circuit
    • Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 12

Go to Step 9

9

Test this 5-volt reference circuit for a short to the throttle actuator control (TAC) motor control 1 or 2 circuits. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct a condition?

--

Go to Step 12

Go to Step 11

10

Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the engine control module (ECM). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 12

--

12

  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 2

Go to Step 13

13

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK