Circuit Description
The engine control module (ECM) provides 5 volts to the following sensors:
| • | The manifold absolute pressure (MAP) sensor |
| • | The engine oil pressure (EOP) sensor |
| • | The fuel tank pressure (FTP) sensor |
| • | The air conditioning (A/C) refrigerant pressure sensor |
| • | The accelerator pedal position (APP) sensor 2 |
| • | The camshaft position (CMP) sensor (2006 Corvette and Cadillac CTSv 6.0 only) |
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 that the voltage is out of tolerance, DTC P0641 sets.
DTC Descriptor
The diagnostic procedure supports the following DTC:
DTC P0641 5-Volt Reference 1 Circuit
Conditions for Running the DTC
| • | The ignition switch is in the ACC, ON, or Start position. |
| • | The ignition voltage is more than 5.23 volts. |
| • | DTC P0641 runs continuously when the above conditions are met. |
Conditions for Setting the DTC
The ECM detects a voltage out of tolerance condition on the 5-volt reference circuit for more than 0.5 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 and/or the Failure Records. |
| • | The control module commands the TAC system to operate in the Reduced Engine Power mode. |
| • | A message center or an indicator displays Reduced Engine Power. |
| • | Under certain conditions the control module commands the engine OFF. |
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.
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 | |
2 |
Does the DTC fail this ignition? | -- | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections |
3 |
Is the voltage within the specified range? | 4.8-5.2 V | Go to Step 5 | Go to Step 4 |
4 | Is the voltage from the previous step more than the specified value? | 5.2 V | Go to Step 8 | Go to Step 6 |
5 |
Is the voltage within the specified range? | 4.8-5.2 V | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 10 |
6 |
Was a component replaced? | -- | Go to Step 13 | Go to Step 7 |
7 | Test the 5-volt reference circuits of all of the sensors connected to this 5-volt reference bus for a short to ground or any sensor low reference circuit. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 |
8 |
Important: If a short to voltage occurs, the A/C refrigerant pressure sensor may be damaged. Test the 5-volt reference circuits of all the sensors connected to this 5-volt reference bus for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9 |
|
Important: If a short to voltage occurs on the fuel tank pressure (FTP) sensor signal circuit, the FTP sensor may be damaged. Test the FTP sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 | |
10 |
Important: If a short to voltage occurs on the MAP sensor signal circuit, the MAP sensor may be damaged. Test the MAP sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 |
11 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
12 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 14 |
14 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
