For 1990-2009 cars

### Circuit Description

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

• | The throttle position (TP) sensor 2

• | The accelerator pedal position (APP) sensor 1

• | The manifold absolute pressure (MAP) sensor

The PCM monitors voltage on the 5-volt reference circuit. If the voltage is higher or lower than required, 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

• | DTCs P0601, P0602, P0603, P0604, P0606, P0607, P0621, P0622, P1621, P1680, P1681, P2610 are not set.

• | The ignition is in the Unlock/Accessory, Run, or Crank position.

• | DTC P0651 runs continuously once the above conditions are met.

### Conditions for Setting the DTC

• | The PCM detects a voltage that is higher or lower than required on the 5-volt reference circuit.

• | The above condition is present for longer 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.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain 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
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. Refer to Throttle Body Assembly Replacement .
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage from the 5-volt reference circuit of the throttle position (TP) sensor 2 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 manifold absolute pressure (MAP) sensor. Refer to Manifold Absolute Pressure Sensor Replacement .
3. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground with a DMM.

Is the voltage within the specified range?

4.8-5.2 V

Go to Intermittent Conditions

Go to Step 9

6 |

1. Monitor the DMM while disconnecting the accelerator pedal position (APP) sensor, the throttle body electrical connector, and the MAP sensor, 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 below:

• | Accelerator Pedal Position Sensor Replacement

• | Throttle Body Assembly Replacement

• | Manifold Absolute Pressure Sensor Replacement

Was a component replaced?

--

Go to Step 12

Go to Step 7

7 | Test this 5-volt reference circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10
8 |

1. Turn ON the ignition, with the engine OFF.
2. Test each 5-volt reference circuit and the MAP sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct a condition?

--

Go to Step 12

Go to Step 10

9 | Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
10 | Test this 5-volt reference circuit for a short to the throttle actuator control (TAC) motor control 1 or 2 circuits. Did you find and correct a condition? | -- | Go to Step 12 | Go to Step 11
11 | Replace the powertrain control module (PCM). Refer to Control Module References 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 | System OK