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 alternative fuels ECM supplies 5 volts to the FRT signal circuit and supplies a ground to the low reference circuit. If the alternative fuels ECM detects a high FRT signal voltage, which is a low temperature indication, this DTC sets.


Conditions for Running the DTC

* The ignition is ON.
* The intake air temperature is more than -10°C (14°F).
* DTCs P0112, and P0113 are not set.



Conditions for Setting the DTC

The alternative fuels ECM detects that the fuel rail temperature sensor voltage is more than 4.95 V for more than 5 seconds.


Action Taken When the DTC Sets

The Alternative Fuels ECM records the operating conditions at the time the diagnostic fails. The Alternative Fuels ECM stores this information in the Freeze Frame and/or Failure Records.


Conditions for Clearing the MIL/DTC

* A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
* A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
* Use a scan tool in order to clear the MIL and the DTC.



Diagnostic Aids

* If a short to a separate 5-volt source occurs this DTC may set, if this is found to be the condition a continuity test to all other PCM circuits will be necessary to diagnose the specific circuit.
* 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 toFuel Rail Temperature (FRT) Sensor Output Voltage vs Temperature Resistance (Electrical Specifications) .
* For an intermittent condition, refer toIntermittent Conditions (Initial Inspection and Diagnostic Overview) .



Test Description

The numbers below refer to the step numbers 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.
8. This step tests the signal circuit of the FRT sensor for a short to another 5.0 volt reference circuit.