GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC K Sierra - 4WD (CNG) 🢒 DTC 🢒 DTC P0187

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. This DTC sets when the FRT signal voltage is below the normal operating range of the sensor.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The alternative fuels ECM detects that the fuel rail temperature sensor voltage is less than 0.05 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
    • 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 .

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls?

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Go to Step 2

Go to Diagnostic System Check - Alternative Fuels (Engine Controls)

2
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the FRT parameter with a scan tool.

Does the scan tool indicate that the FRT is less than the specified value?

0.05 V

Go to Step 4

Go to Step 3

3
  1. Observe the Freeze Frame and/or the Failure records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame and/or the Failure records data.

Does the DTC fail this ignition cycle?

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Disconnect the harness connector of the FRT sensor. Refer to Fuel Temperature Sensor Replacement .
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the FRT parameter with a scan tool.

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 5

5
  1. Turn OFF the ignition.
  2. Disconnect the PCM. Refer to Powertrain Control Module Replacement in Engine Controls in the C/K Pickup Service Manual.
  3. Test the signal circuit of the FRT sensor for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual.

Did you find and correct the condition?

--

Go to Step 8

Go to Step 7

6

Replace the FRT sensor. Refer to Fuel Temperature Sensor Replacement .

Did you complete the replacement?

--

Go to Step 8

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7

Replace the alternative fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 8

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8
  1. Use the scan tool in order to clear the DTCs from the following control modules:
    2. • alternative fuels ECM
    • PCM
  2. Turn OFF the ignition for 30 seconds.
  3. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 9

Go to Step 2

9

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?

--

Go to Diagnostic Trouble Code (DTC) List

System OK