EVAP Fuel Vapor Temp Sensor Circ Low Voltage


This indicates that the PCM has detected a malfunction in the evaporative fuel vapor temperature sensor circuit. The EVAP system consists of components including (but not limited to) the gas cap, fuel lines, charcoal canister, purge valve, system pressure and flow sensors, electrical wiring and connectors, vacuum lines, the fuel tank, and fuel vapor hoses. The fuel vapor temperature sensor is used to monitor fuel vapor temperature in the charcoal canister or fuel tank.

Code Set Parameters




Common Causes

These may include a faulty fuel vapor temperature sensor, a faulty purge control solenoid, clogged or broken charcoal canister, broken or cracked vacuum or fuel vapor hoses, a faulty pressure or flow sensor, or a bad PCM. PCM failure is rare.

Common Misdiagnosis



  • The purge control solenoid opens the purge control valve (with the engine running) and allows engine vacuum to draw the fuel vapors into the engine where they are burned along with the liquid fuel. The charcoal canister is typically located near the fuel tank, which is underneath the vehicle
  • The fuel vapor and vacuum hoses can be quite long and subject to damage from the elements and road debris. Evaporative fuel vapor temperature is monitored using an electronic sensor in the charcoal canister or fuel tank (depending upon the individual automaker)
  • The evaporative fuel vapor temperature sensor is typically of the variable resistance type with a three wire connector
  • A voltage reference signal (usually 5-volts) is supplied to the sensor along with a system ground
  • The third wire is normally the signal wire which provides the fuel vapor temperature input to the PCM
  • When the evaporative fuel vapor temperature is low, sensor resistance is higher making the reference signal voltage lower
  • As evaporative fuel vapor temperature rises, resistance decreases and allows reference signal voltage to become higher
  • The PCM sees these variations in evaporative fuel vapor temperature sensor voltage as fuel vapor temperature and reacts accordingly
  • If the voltage remains at the maximum level, or fails to meet a minimum desired level for an abnormal period of time, a code will be stored and a malfunction indicator lamp may be illuminated
  • Evaporative fuel vapor temperature codes can be best diagnosed by beginning with the evaporative fuel vapor temperature sensor
  • Disconnect the electrical connector from the evaporative fuel vapor temperature sensor and check for reference voltage and ground signals using the digital volt/ohmmeter
  • If either of these signals is not detected, disconnect the PCM connector and perform a resistance and continuity test of all related circuits
  • Replace or repair open, shorted, disconnected, or corroded circuitry as required
  • Clear the codes and test drive the vehicle to ensure that the repair was successful. If a voltage and ground signal were detected, use the digital volt/ohmmeter and the temperature to resistance chart from the manufacturer’s service manual to test the evaporative fuel vapor temperature sensor itself
  • Compare your findings with manufacturer’s specifications and replace the sensor if they fail to coincide
  • Use the infrared thermometer to determine the actual fuel vapor temperature and base your calculations on the live data
  • Several tools may be needed to successfully diagnose this code
  • A suitable scanner (or code reader), a digital volt/ohmmeter, a manufacturer’s service manual (or the equivalent), an infrared thermometer with a laser pointer, and a smoke machine will be most helpful in performing a successful diagnosis
  • Begin with a visual inspection of all wiring and connectors
  • Reset the codes and test-drive the vehicle. If an evaporative fuel vapor temperature code is present (and fuel vapor temperature seems to be within specifications), visually inspect vacuum and fuel vapor hoses for cracks, splits, kinks, or breakage, and repair as necessary
  • Start the engine and allow it to enter closed loop operation
  • Listen carefully to the purge control solenoid
  • This is normal
  • Replace the canister as necessary
  • It should act like an “on/off” valve that is activated by completing a circuit that is normally rated for battery voltage
  • Check manufacturer’s specs before applying voltage to the solenoid
  • If an evaporative fuel vapor temperature code is still present, inspect electrical connectors and wiring for signs of corrosion or damage and repair as required
  • Compare your findings to manufacturer’s specifications and repair as necessary
  • Reset the codes and retest the vehicle
  • Keep in mind, that following repairs, multiple drive cycles may be necessary to verify that the fault condition has been rectified. If all system circuitry and components appear to be working according to manufacturer’s specifications, suspect a defective PCM
  • PCM failure is rare and should be considered only as a last resort
  • PCM replacement will require reprogramming of certain control modules by qualified personnel.