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DTC P1494: Leak Detection Pump SW Or Mechanical Fault: Testing

  1. Turn the ignition on. With the DRBIII(R), read DTCs. Is the Good Trip counter displayed and equal to zero? If yes, go to next step. If no, go to step  7 .
  2. Turn the ignition off. Disconnect the vacuum supply hose at the LDP. Connect a vacuum gauge to the disconnected vacuum supply hose at the LDP. Start the engine. Allow the engine to idle. Read the vacuum gauge. Does the vacuum gauge read at least 13 in. Hg? If yes, go to next step. If no, repair vacuum leak or vacuum obstruction as necessary.
  3. Turn the ignition off. Disconnect the LDP harness connector. Turn the ignition on. With the DRBIII(R) in Inputs/Outputs, read the LDP Sw state. While observing the LDP Sw state, connect a jumper wire between a 12-volt source and the LDP switch sense circuit in the LDP harness connector. Did the LDP Sw state change when the jumper was connected? If yes, replace the LDP. If no, go to next step.
  4. Turn the ignition off. Disconnect the PCM harness connectors. Measure the resistance between ground and the LDP switch sense circuit in the LDP harness connector. Is the resistance less than 5.0 ohms? If yes, repair the LDP switch sense circuit for a short to ground. If no, go to next step.
  5. Measure the resistance of the LDP switch sense circuit between the LDP harness connector and the PCM harness connector. Is the resistance less than 5.0 ohms? If yes, go to next step. If no, repair the LDP switch sense circuit for an open.
  6. There are no possible causes remaining, replace PCM.
    7. WARNING: When the engine is operating, DO NOT stand in a direct line with the fan. DO NOT put your hands near the pulleys, belts or fan. DO NOT wear loose clothing.
    NOTE: Use the Freeze Frame Data to help duplicate the conditions that set the DTC. Pay particular attention to the DTC set conditions, such as, VSS, MAP, ECT, and Load.
  7. Conditions that set DTC are not present at this time. The following list may help in identifying the intermittent condition:
    • With engine running at normal operating temperature, wiggle related wiring harness while monitoring related parameters on scan tool. If voltage changes or DTC sets while wiggling wiring harness, repair connectors or wiring harness where wiggling caused voltage to change or DTC to set.
    • Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires.
    • Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals.
    • Refer to any Technical Service Bulletin (TSB) that may apply.
    • Perform a wiggle test of the LDP wiring while the circuit is actuated with the DRBIII(R). Listen for the LDP to quit actuating. Also watch for the Good Trip counter to change to zero.

    If a problem is found, repair as necessary. If no problems are found, test is complete.

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