Circuit Description
The fuel tank temperature (FTT) sensor is a variable resistor that measures the temperature of the fuel in the CNG fuel tank. The alternative fuels ECM supplies 5 volts to the FTT signal circuit and supplies a ground to the low reference circuit. This DTC sets when the FTT 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 tank 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 FTT 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 FTT 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 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? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) | ||||
2 |
Does the scan tool indicate that the FTT is less than the specified value? | 0.05 V | Go to Step 4 | Go to Step 3 | ||||
3 |
Does the DTC fail this ignition cycle? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||
4 |
Does the scan tool indicate that the FTT sensor voltage is more than the specified value? | 4.6 V | Go to Step 5 | Go to Step 7 | ||||
5 | Measure the voltage from the 5 volt reference circuit of the FTT sensor with a DMM. Does the DMM display a voltage near the specified value? | 5 V | Go to Step 8 | Go to Step 6 | ||||
6 |
Important: The 5 volt reference circuit also supplies voltage to the fuel tank pressure (FTP) sensor. Disconnect the FTP sensor in order to determine if the FTP sensor is the cause of the shorted condition. Test the 5 volt reference circuit of the FTT 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 10 | Go to Step 9 | ||||
7 |
Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 | ||||
8 | Replace the FTT sensor. The FTT sensor is not serviceable separately from the HPL. Refer to High Pressure Lock-Off Solenoid Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||
9 | Replace the Alternative Fuels ECM. Refer to Alternative Fuels Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||
10 |
Does the DTC run and pass? | -- | Go to Step 11 | Go to Step 2 | ||||
11 | 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 | |||||
