Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provide an overview of each diagnostic category. |
DTC Descriptors
DTC P0641: 5-Volt Reference 1 CircuitDTC P0651: 5-Volt Reference 2 Circuit
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 2 Circuit | P0651 | P0532 | P0651 | -- |
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit | P0641 | P0452 | P0641 | -- |
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 2 circuit | P0651 | P0107 | P0651 | -- |
Exhaust Gas Recirculation (EGR) Valve 5-Volt Reference 1 Circuit | P0405, P0406 | P0404, P0405 | P0406 | -- |
Circuit/System Description
The control module has 2 internal 5-volt reference busses called 5-volt reference 1 and 5-volt reference 2. Each reference bus provides 5-volt reference circuits for more than one sensor. Therefore, a fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference bus. The control module monitors the voltage on the 5-volt reference busses.
The 5-volt reference 1 bus provides 5 volts to the following sensors:
| • | The fuel tank pressure (FTP) sensor |
| • | The exhaust gas recirculation (EGR) valve |
The 5-volt reference 2 bus provides 5 volts to the following sensors:
| • | The manifold absolute pressure (MAP) sensor |
| • | The air conditioning (A/C) refrigerant pressure sensor |
Conditions for Running the DTC
| • | DTCs P0601, P0602, P0603, P0604, P0605, P0606, P0607, P060D, P062F and P2610 are not set. |
| • | The ignition is ON. |
| • | The ignition voltage is more than 9.5 volts. |
| • | DTCs P0641 and P0651 run continuously when the above conditions are met. |
Conditions for Setting the DTC
The control module detects a voltage out of tolerance condition on the 5-volt reference 1 or 2 bus 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/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. |
Reference Information
Schematic Reference
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
P0641
Observe the FTP sensor voltage parameter with a scan tool with the ignition ON and the engine OFF. The scan tool should display 3.6-4.8 volts for a normally operating system.
P0651
With the ignition ON and the engine OFF, observe the A/C Refrigerant Pressure-A/C High Side Pressure parameter with a scan tool. The scan tool should display 0.2-4.9 volts or 9-453 psi for a normally operating system.
Circuit/System Testing
Important:
• Additional DTCs will set when disconnecting the components. • A short to voltage on the signal circuit of certain components may cause this DTC to set.
- Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC.
- Ignition ON, measure for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.
- Connect each component associated with the 5-volt reference circuit, one at a time, while monitoring the voltage. The voltage should not change more than 1 volt.
| ⇒ | If the voltage is less than the specified value, test for a short to ground on all the 5-volt reference circuits. If all circuits test normal, replace the control module. |
| ⇒ | If the voltage is greater than the specified value, test for a short to voltage on all the 5-volt reference circuits, or the signal circuit, for each component associated with the appropriate 5-volt reference circuit. If all circuits test normal, replace the control module. |
| ⇒ | If the voltage display changes more than the specified value when a component is connected, replace the component. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for engine control module (ECM) replacement, setup, and programming |
