Circuit Description
The fuel rail temperature (FRT) sensor is a variable resistor that measures the temperature of the fuel in the compressed natural gas (CNG) fuel rail. The fuel injector control module (FICM) supplies 5 volts to the FRT signal circuit and supplies a ground to the low reference circuit. The FICM monitors the FRT sensor voltage and communicates the data to the powertrain control module (PCM) by a dedicated pulse width modulated (PWM) circuit. This DTC sets when the FRT signal voltage is below the normal operating range of the sensor.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0187 Fuel Rail Temperature Sensor Circuit Low Voltage
Conditions for Running the DTC
| • | The ignition is ON. |
| • | The intake air temperature is more than -35°C (-31°F). |
Conditions for Setting the DTC
| • | The fuel rail temperature sensor voltage is less than 0.05 volt. |
| • | The condition exists for more than 5 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the 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. |
Diagnostic Aids
| • | Use the Temperature vs Resistance table in order to test the FRT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor could result in a driveability condition. If the engine has sat overnight, the FRT sensor and the intake air temperature values should display within a few degrees. If the temperatures are not within 3°C (5°F), refer to Fuel Rail Temperature Sensor Output Voltage Versus Temperature Resistance . |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the condition exists.
-
This step determines if an open low reference circuit is the cause of the condition. If DTC P0192 is also set, an open low reference circuit may be the cause. The FRT sensor, and the fuel rail pressure (FRP) sensor share a low reference circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
Does the scan tool indicate that the FRT is less than the specified value? | 0.05 V | Go to Step 3 | Go to Step 4 | |
Is DTC P0192 also set? | -- | Go to Step 8 | Go to Step 5 | |
4 |
Does the DTC fail this ignition cycle? | -- | Go to Step 5 | Go to Diagnostic Aids |
5 |
Does the scan tool indicate that the FRT sensor voltage is more than the specified value? | 4.6 V | Go to Step 6 | Go to Step 7 |
6 | Probe the low reference circuit of the FRT with a test lamp connected to B+. Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 8 |
7 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 |
8 | Test the low reference circuit of the FRT for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the G/H Van Service Manual. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 |
9 | Inspect for proper terminal contact at the harness connector of the FRT sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the G/H Van Service Manual. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 |
10 | Inspect for proper terminal contact at the harness connector of the fuel injector control module (FICM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the G/H Van Service Manual. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 |
11 | Replace the FRT sensor. Refer to Fuel Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
12 | Replace the FICM. Refer to Fuel Injector Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 14 |
14 | With a scan tool, select Capture Info in order to observe the stored information. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
