Circuit Description
The engine control module (ECM) uses the fuel rail pressure (FRP) sensor to determine fuel pressure to the fuel injectors. This is then compared to the calculated target fuel pressure as determined by the ECM. The ECM adjusts the FRP by modulating the duty cycle of the control driver of the fuel pressure regulator. Injector pulse duration is determined by the measured rail pressure and the target injection fuel into each cylinder. If a sensor circuit malfunction is detected, or the commanded fuel injection pump flow is not within the proper range for a given engine load and speed, DTC will be set.
DTC Description
This diagnostic information supports the following DTC:
DTC P1094 Fuel Rail Pressure Low During Idle or Decel Fuel Cut-Off (DFCO)
Conditions for Running the DTC
| • | DTCs P0192, P0193, P0642, P0643 are not set. |
| • | The ignition is ON. |
Conditions for Setting the DTC
The difference between FRP sensor and commanded fuel injection pump flow is more than 30 MPa.
Action Taken When the DTC Sets
| • | The control module stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records. |
| • | The driver information center, if equipped, may display a message. |
Conditions for Clearing the DTC
| • | 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 non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| • | If you have to prime the fuel system, inspect for the following conditions: |
| - | A restricted fuel supply line |
| - | A fuel supply line air leak--Refer to Fuel System Diagnosis |
| • | If the condition is still intermittent, refer to Intermittent Conditions . |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | |
2 | Is DTC P1093 also set? | -- | Go to DTC P1093 | Go to Step 3 |
3 | Inspect for fuel contamination. Refer to Contaminants-in-Fuel Diagnosis . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 4 |
4 | Attempt to start the engine. Does the engine start and continue to run? | -- | Go to Step 5 | |
5 | Is the customer concern also a surging idle? | -- | Go to Step 6 | |
6 |
Does the FRP regulator fuel flow measure more than the specified value? | 12 000 mm³ | Go to Step 7 | Go to Diagnostic Aids |
7 | Test the fuel pressure regulator solenoid control circuit between the engine control module (ECM) and the fuel pressure regulator for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 8 |
8 | Test for an intermittent or poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
9 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 11 |
11 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
