P0188

DTC P0188

Circuit Description

The fuel rail temperature (FRT) sensor is a variable resistor that measures the temperature of the fuel in the 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 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.

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 more than 4.95 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 Temperature Sensor Replacement.
- For an intermittent condition, refer to Intermittent Conditions.

Test Description

The number below refers to the step number on the diagnostic table.

4. 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.