P1494 Code failures by brands


Description of DTC code P1494

The EVAP (evaporative emission control system) system captures and keeps fuel vapors in a sealed tank. In this way, they cannot escape into the environment. Although these systems generally use a vacuum to check the system for proper operation, many manufacturers use an air pump. This air pump is known as a leak detection pump. To determine if fuel vapors are leaking, the air pump pressurizes the system to around 0.25 PSI during the self-tests

A diaphragm operates the leak detection pump. It consists of a sealed vessel divided into two halves by the diaphragm, which has a constant pressure by a spring. The lower half is connected to the EVAP. One side of the diaphragm has an opening to allow atmospheric air to enter. On the other hand, the upper half is connected to the engine vacuum, and one side to the atmospheric opening.

The pump diaphragm is connected to a metal shaft. It activates an on/off switch as the diaphragm moves up and down during the pumping process. The PCM uses this switch for diagnostic purposes but also to know the position of the diaphragm regarding the PCM. This position is the basis for a pump solenoid activation mechanism during a normal operating condition.

If the PCM has detected that the reed switch or leak detection pump control switch has not changed once the self-test process has begun because of a failure of the solenoid, the control circuit, or the diaphragm itself, the fault code P1494 OBDII will be set.

Symptoms of fault code P1494

  • Check Engine light ON.
  • Strong fuel odors are perceived.
  • The vehicle fails the emissions tests.

Causes of OBD2 P1494

Reasons to set the P1494 OBD2 DTC P1494 OBD2 code :

  • The system circuit may have damage to the wires or connectors, resulting in a short or open circuit.
  • Vacuum lines may be blocked or damaged, resulting in leaks.
  • The leak detection pump may be faulty.

Possible solutions of the DTC code P1494

Steps to troubleshoot the P1494 OBDII diagnostic code:

  • Scan to check if other error codes are stored related to the EVAP If these show any problem in the wiring, sensors, or control circuits, repair them before P1494.
  • Consult the TSBs as well as the locations of the EVAP components and vacuum lines. Then, keep the engine off, disconnect the vacuum line leading from the pump to the engine and disconnect the line from the pump. By using a vacuum gauge connected to the line, start the engine and check if the vacuum is at least 13 in/ Hg. Compare the result obtained with the specified result. If they do not match, check for damage to the vacuum line. Repair if necessary.
  • Locate the pump switch sensing circuit, and verify the resistance of this wire between the connectors is not greater than 5 ohms. If this value is right, check there is no damage to the cable that might cause an open circuit. But if the resistance exceeds the established limit, check that it is not due to a short to ground. Repair as required.
  • Connect a scanner and check the status of the switch while the power switch is on. Apply direct current from the battery to the switch sensing circuit. If the status displayed on the scanner does not change when the current is applied, the pump may be in bad condition. Make appropriate corrections.

Codes related to P1494

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