Buick Regal: DTC P127C, P128A, P128B, P16E4, or P16E5

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 provides an overview of each diagnostic category.

DTC Descriptors

DTC P127C

Fuel Rail Pressure Sensor 2 Circuit Low Voltage

DTC P128A

Fuel Rail Pressure Sensor 1 Internal Performance

DTC P128B

Fuel Rail Pressure Sensor 2 Internal Performance

DTC P16E4

Sensor Communication Circuit 3 Low Voltage

DTC P16E5

Sensor Communication Circuit 3 High Voltage

Diagnostic Fault Information

Typical Scan Tool Data

Fuel Rail Pressure Sensor

Fuel Rail Pressure Sensor 2

Circuit/System Description

The fuel rail pressure sensor transmits fuel pressure and temperature information by serial data using the Society of Automotive Engineers (SAE) J2716 Single Edge Nibble Transmission (SENT) protocol. The fuel rail pressure sensor internal microprocessor allows 4 separate sensor outputs from one 3 wire sensor. The engine control module (ECM) supplies the fuel rail pressure sensor with a 5 V reference circuit, a low reference circuit, and an asynchronous signal/serial data circuit. The asynchronous signal means communication is only going from the fuel rail pressure sensor to the ECM. The ECM decodes the serial data signal into separate voltages which are displayed on a scan tool as the voltage inputs from the Fuel Temperature Sensor, Fuel Rail Pressure Sensor and Fuel Rail Pressure Sensor 2.

Conditions for Running the DTC

P128A or P128B

• DTC P128F, P16E4 or P16E5 is not set.
• Ignition is ON.
• The DTCs run continuously when the above condition are met.

P127C, P16E4 or P16E5

• Ignition is ON.
• No DTC clear code
• The DTCs run continuously when the above condition are met.

Conditions for Setting the DTC

P127C

The engine control module detects the fuel pressure sensor 2 SENT digital read value is less than or equal to 94 for greater than 1 s.

P128A

The engine control module detects fuel pressure sensor 1 SENT digital read value is greater than 4, 089 for greater than 1 s

P128B

The engine control module detects fuel pressure sensor 2 SENT digital read value is greater than 4, 089 for greater than 1 s

P16E4

The engine control module detects fuel pressure sensor SENT signal shorted low for greater than 1 s

P16E5

The engine control module detects fuel pressure sensor SENT signal shorted high for greater than 1 s

Action Taken When the DTC Sets

DTCs P127C, P128A, P128B, P16E4 and P16E5 are Type A DTCs.

Conditions for Clearing the DTC

DTCs P127C, P128A, P128B, P16E4 and P16E5 are Type A DTCs.

Diagnostic Aids

A high resistance condition on the fuel rail pressure sensor circuits could cause a DTC to set.

Reference Information

Schematic Reference

Engine Controls Wiring Schematics (LTG)

Connector End View Reference

Component Connector End View Index

Powertrain Component View

Powertrain Component Views

Description and Operation

Fuel System Description

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Ignition ON/Vehicle in Service Mode.

2. Verify that DTC P0641, P0651, P0697, P06A3, or P06D2 is not set.

• If any of the DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

• Go to next step: If none of the DTCs are set

3. Verify that DTC P0182, P0183, P0187, P0188, P111F, P126E, P126F, P128A, or P128B are not set.

• If DTC P128A or P128B are the only DTCs set

Test or replace the B310 Fuel Pressure/Temperature Sensor.

• If DTC P0183, P0184, P0187, P0188, P111F, P126E, P126F, P127C, P16E4, or P16E5 is set with any of the DTCs

Refer to Circuit/System Testing.

• Go to next step: If none of the DTCs are set

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 data.

5. Verify the DTC does not set.

• If the DTC sets

Refer to Circuit/System Testing.

• Go to next step: If the DTC does not set

6. All OK.

Circuit/System Testing

NOTE: Disconnecting the fuel rail pressure sensor harness connector causes additional DTCs to set.

1. Ignition/Vehicle OFF, and all vehicle systems OFF, disconnect the harness connector at B310 Fuel Pressure/Temperature Sensor. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 5 Ω between the low reference circuit terminal 1 and ground.

• If 5 Ω or greater

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for less than 2 Ω in the low reference circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K20 Engine Control Module.

• Go to next step: If less than 5 Ω

3. Ignition ON.

4. Test for 4.8 - 5.2 V between the 5 V reference circuit terminal 3 and ground.

• If less than 4.8 V

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the 5 V reference circuit and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the 5 V reference circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K20 Engine Control Module.

• If greater than 5.2 V

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
2. Test for less than 1 V between the 5 V reference circuit and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K20 Engine Control Module.

• Go to next step: If between 4.8 - 5.2 V

5. Test for 4.8 - 5.2 V between the signal circuit terminal 2 and ground.

• If less than 4.8 V

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the signal circuit and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the signal circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K20 Engine Control Module.

• If greater than 5.2 V

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
2. Test for less than 1 V between the signal circuit and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K20 Engine Control Module.

• Go to next step: If between 4.8 - 5.2 V

6. Replace the B310 Fuel Pressure/Temperature Sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Fuel Injection Fuel Rail Fuel Pressure Sensor Replacement for B310 Fuel Pressure/Temperature Sensor.
• Control Module References for control module replacement, programming, and setup.

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