P0188

DTC P0188

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 above the normal operating range of the sensor.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0188 Fuel Rail Temperature Sensor Circuit High Voltage

CONDITIONS FOR RUNNING THE DTC
- The ignition is ON.
- The intake air temperature (IAT) is more than -10°C (+14°F).
- DTCs P0112, P0113, or P1207 are not set.

CONDITIONS FOR SETTING THE DTC
- The FRT sensor voltage is more than 4.95 volts.
- 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 IAT values should display within a few degrees. If the temperatures are not within 3°C (5°F), refer to Fuel Rail Temperature (FRT) Sensor Replacement.
- For an intermittent condition, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Step 1 - Step 9:

Step 10 - Step 13:

The number below refers to the step number on the diagnostic table.
4. This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.