Home » GM 6.5 » GM/Detroit 6.5L – Engine Management – FUEL CONTROL – FUEL TEMPERATURE SENSOR

GM/Detroit 6.5L – Engine Management – FUEL CONTROL – FUEL TEMPERATURE SENSOR


The fuel temperature sensor is part of the optical sensor (see figure 5-36). It is a thermistor that controls signal voltage to the PCM. Voltage from the sensor will vary inversely to fuel temperature (i.e. high temperature equals low voltage; low temperature equals high voltage). Resistance values for the sensor at various temperatures are the same as those for other temperature sensors given earlier in this book (see ECT and IAT sensor discussions).

Fuel Temperature Sensor Circuit Operation
The PCM provides a reference signal to the fuel temperature sensor on CKT 1578 (figure 5-32). As fuel temperature changes, the sensor will alter the strength of the voltage. By monitoring CKT 1578, the PCM knows fuel temperature and can take this into consideration when determining fuel delivery rates. Ground for the sensor is provided on CKT 987, which is shared with the optical sensor.

DTC 42 — “Fuel Temperature Circuit Low (High Temperature Indicated)”
DTC 42 sets when the PCM detects lower-than-normal voltage on CKT 1578. The code will set when fuel temperature is greater than 102°C (215°F) for more than 2 seconds. In addition to being caused by high fuel temperatures, DTC 42 could be caused by a short to ground in CKT 1578.

DTC 43 — “Fuel Temperature Circuit High (Low Temperature Indicated)”
DTC 43 sets when CKT 1578 voltage is higher than normal. The condition for this code to set is fuel temperature less than -14°C (6°F) when the engine has been running for longer than 2 minutes. DTC 43 could also be caused by opens in CKTs 1578 or 987, or a faulty connection at the sensor or PCM.


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