| • | 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 provides an overview of each diagnostic category. | 
Circuit  | Short to Ground  | Open/High Resistance  | Short to Voltage  | 
|---|---|---|---|
Accelerator Pedal Position (APP) Sensor 1 5-Volt Reference 2 Circuit  | P0652  | P2122  | P0653  | 
Accelerator Pedal Position (APP) Sensor 2 5-Volt Reference 3 Circuit  | P0698  | P2127  | P0699  | 
Air Conditioning (A/C) Refrigerant Pressure Sensor 5-Volt Reference 3 Circuit  | P0698  | P0532  | P0699  | 
Crankshaft Position Sensor 5-Volt Reference 3 Circuit  | P0698  | P0335  | P0699  | 
Engine Oil Pressure Sensor 5-Volt Reference 3 Circuit  | P0698  | P0520  | P0699  | 
Exhaust Camshaft Position Sensor 1 5-Volt Reference 2 Circuit  | P0652  | P0368  | P0653  | 
Fuel Rail Pressure Sensor 5-Volt Reference 1 Circuit  | P0642  | P0192  | P0643  | 
Fuel Tank Pressure (FTP) Sensor 5-Volt Reference 1 Circuit  | P0642  | P0452  | P0643  | 
Intake Camshaft Position Sensor 1 5-Volt Reference 2 Circuit  | P0652  | P0343  | P0653  | 
Manifold Absolute Pressure (MAP) Sensor 5-Volt Reference 1 Circuit  | P0642  | P0107  | P0643  | 
Throttle Position (TP) Sensor 1 5-Volt Reference 3 Circuit  | P0698  | P0122  | P0699  | 
Throttle Position (TP) Sensor 2 5-Volt Reference 3 Circuit  | P0698  | P0222  | P0699  | 
Intake Air Pressure and Temperature Sensor 5-Volt Reference 1 Circuit  | P0642  | P0238  | P0643  | 
The engine control module (ECM) has 3 internal 5-volt reference busses called 5-volt reference 1, 5-volt reference 2, and 5-volt reference 3. 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 ECM monitors the voltage on the 5-volt reference busses.
The 5-volt reference 1 bus provides 5 volts to the following sensors:
| • | The manifold absolute pressure (MAP) sensor | 
| • | The clutch apply sensor | 
| • | The fuel rail sensor | 
| • | The fuel tank pressure (FTP) sensor | 
| • | The intake air pressure and temperature sensor | 
The 5-volt reference 2 bus provides 5 volts to the following sensors:
| • | The accelerator pedal position (APP) sensor 1 | 
| • | The exhaust camshaft position (CMP) sensor | 
| • | The intake camshaft position (CMP) sensor | 
The 5-volt reference 3 bus provides 5 volts to the following sensors:
| • | The APP sensor 2 | 
| • | The crankshaft position (CKP) sensor | 
| • | The air conditioning (A/C) refrigerant pressure sensor | 
| • | The throttle position (TP) sensor 1 and 2 | 
| • | The brake booster vacuum sensor | 
| • | DTCs P0601, P0602, P0603, P0604, and P0606 are not set. | 
| • | The ignition is in Run, or Crank. | 
| • | The ignition voltage is more than 5.23 volts. | 
| • | DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698, and P0699 run continuously when the above conditions are met. | 
These DTCs set when the ECM detects a voltage out of tolerance condition on the 5-volt reference 1, 2 or 3 bus for more than 3 seconds.
These DTCs set when the ECM detects a low voltage condition on the 5-volt reference 1, 2, or 3 bus for more than 3 seconds.
These DTCs set when the ECM detects a high voltage condition on the 5-volt reference 1, 2, or 3 bus for more than 3 seconds.
DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698, and P0699 are Type A DTCs.
DTCs P0641, P0642, P0643, P0651, P0652, P0653, P0697, P0698, and P0699 are Type A DTCs.
| • | It may be possible to locate the fault by disconnecting one component at a time from the 5-volt reference circuit while viewing the 5-Volt Reference circuit parameter on the scan tool. The scan tool parameter would change from Fault to OK when the source of the fault is disconnected. | 
| • | If all 5-volt reference components have been disconnected and a Fault is still indicated, the fault may exist in the wiring harness. | 
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Control Module References for scan tool information
With the ignition ON and the engine OFF, observe the 5-volt Reference 1, 2, and 3 parameters. The scan tool should display OK for a normally operating system.
Important: Additional DTCs will set when disconnecting the components.
Important: A short to voltage on the signal circuit of certain components may cause this DTC to set.
| ⇒ | If the voltage is less than the specified range, test for a short to ground on all the 5-volt reference circuits. If all circuits test normal, replace the ECM. | 
| ⇒ | If the voltage is greater than the specified range, test for a short to voltage on all the 5-volt reference circuits. If all circuits test normal, replace the ECM. | 
| ⇒ | If the voltage display increases greater than the specified value when a component is connected, test the signal circuit for a short to voltage. If all circuits test normal, replace the ECM. | 
| ⇒ | If the voltage display decreases more than the specified value when a component is connected, replace the component. | 
| • | Diagnostic Trouble Code (DTC) List - Vehicle for ECM replacement, setup, and programming. | 
With the ignition ON and the engine OFF, observe the 5-Volt Reference 1, 2 and 3 parameters. The scan tool should display 5-volt reference circuit status OK for a normally operating system.