P0641
DTC P0641 or P0651
DTC Descriptors
DTC P0641
- 5-Volt Reference 1 Circuit
DTC P0651
- 5-Volt Reference 2 Circuit
Diagnostic Fault Information
Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
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.
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.
1. Ignition OFF, disconnect the harness connector of all appropriate sensors for the applicable DTC.
2. Ignition ON, measure for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.
• 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.
3. 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 display changes more than the specified value when a component is connected, replace the component.
Repair Instructions
Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests
* Exhaust Gas Recirculation Valve Replacement
* Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
* Programming and Relearning for engine control module (ECM) setup and programming. Programming and Relearning
* Fuel Tank Pressure Sensor Replacement
* Manifold Absolute Pressure Sensor Replacement.