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, DTCs will be set.
DTC Description
This diagnostic procedure supports the following DTC:
DTC P1093 Fuel Rail Pressure Low During Power Enrichment
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 the commanded fuel pressure and the actual fuel pressure is more than 20 MPa.
OR
The FRP regulator fuel flow is more than 19 200 mm³ at 800 RPM, or more than 44 400 mm³ at 2,000 RPM.
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. |
The engine will be in reduced power mode to replace using no more than 2,000 RPM.
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. |
Diagnostic Aids
| • | This DTC does not set for an idle condition. |
| • | The following are some conditions that may cause DTC P0087 and DTC P1093 to set: |
| - | A restricted fuel filter |
| - | Excessive fuel return to the tank |
| - | A fuel injection pump failure |
| - | A fuel pressure regulator (RPCV) failure |
| • | 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. |
| • | A sticking fuel pressure regulator may set this DTC. Refer to Fuel System Diagnosis - High Pressure Side. Perform this test under the conditions for which the DTC set. |
| • | If power enhancing devices have been attached to the fuel rail pressure sensor circuits, this DTC may set and adversely effect the fuel system components. Refer to Fuel System Diagnosis - High Pressure Side. |
| • | If the condition is still intermittent, refer to Intermittent Conditions. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the fuel temperature is high enough to set DTC P0168, the fuel may be thin enough to cause this DTC to set.
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The engine will not start if the fuel leak is large enough.
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This step inspects for an inaccurate fuel rail pressure sensor.
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This step inspects for fuel leaks into the engine oil.
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This step inspects for a restriction in the fuel system between the fuel injection pump and the fuel tank.
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This test verifies the fuel injection pump is able to supply maximum fuel pressure at idle. The fuel injection pump should be able to create 145-158 MPa at idle. At higher ambient temperatures, the fuel pressure will be lower, but still more than 145 MPa.
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This step inspects for a restriction in the fuel system between the fuel injection pump and the fuel tank that may only cause symptoms at higher engine speed and load conditions.
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This step verifies to see if the fuel rail pressure sensor wiring and ECM are functioning normally.
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If the vacuum is still too high in the fuel supply system after replacing the fuel filter, there is a restriction in the fuel supply lines or sending unit in the fuel tank.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
Is DTC P0168 or P0090 also set? | -- | Go to Step 3 | ||
3 |
Important: Failure to wait until there is no engine control module (ECM) communications with the scan tool will result in misdiagnosis. Is the FRP Regulator Command more than the specified value? | 20% | Go to Step 4 | Go to Step 16 |
Attempt to start the engine. Does the engine start and idle? | -- | Go to Step 5 | ||
Is the Actual Fuel Rail Pressure Parameter within the specified range? | 1-1.8 MPa | Go to Step 6 | Go to Step 10 | |
Inspect for fuel contamination. Refer to Contaminants-in-Fuel Diagnosis. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 7 | |
Does the vacuum measure less than the specified value through the entire RPM range? | 5 inches | Go to Step 8 | Go to Step 11 | |
Is the Actual Fuel Rail Pressure parameter more than the specified value? | 145 MPa | Go to Step 9 | ||
|
Important: If the fuel temperature is near 121°C (250°F) during the duplication of the complaint or in the Failure Records for this DTC, inspect for a restriction in the fuel cooler air flow or the fuel heater always ON. Refer to Fuel Heater Always On.
Does the vacuum measure less than the specified value through the entire operating range? | 12 inches | Go to Diagnostic Aids | Go to Step 11 | |
Does the Actual Fuel Rail Pressure measure more than the specified value? | 175 MPa | Go to Step 15 | Go to Step 14 | |
11 | Replace the fuel filter. Refer to Fuel Filter Replacement. Did you complete the replacement? | -- | Go to Step 12 | -- |
Does the vacuum measure less than or equal to the specified value? | 5 inches at idle to WOT, no load 12 inches at high speed, high load | Go to Step 17 | Go to Step 13 | |
13 | Repair the restriction in the fuel supply lines between the fuel tank and the fuel injection pump. Refer to Fuel System Diagnosis. Did you complete the repair? | -- | Go to Step 17 | -- |
14 | Inspect the fuel rail pressure sensor signal circuit for a short to ground. Repair as necessary. Refer to Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
15 | Replace the fuel rail pressure sensor. Refer to Fuel Injection Fuel Rail Fuel Pressure Sensor Replacement. Did you complete the replacement? | -- | Go to Step 17 | -- |
16 | Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 17 | -- |
17 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 18 |
18 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
