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

  1. Turn ignition on, with engine off. Using scan tool, read DTCs. If GLOBAL GOOD TRIP counter is displayed and displayed count is "0", go to next step. If GLOBAL GOOD TRIP counter is not displayed or displayed count is not "0", go to step  7.
  2. Turn ignition off. Disconnect engine vacuum supply hose at Leak Detection Pump (LDP). LDP is located on top of fuel tank. See Figure. Install a vacuum gauge to disconnected vacuum hose. Start engine and observe vacuum gauge. If vacuum is 13 in. Hg or more, go to next step. If vacuum is less than 13 in. Hg, repair vacuum leak or vacuum obstruction as necessary.
  3. Turn ignition off. Disconnect LDP connector. Turn ignition on. With scan tool in INPUTS/OUTPUTS, read LEAK DETECT SW state. Connect a jumper wire between Orange/Red wire and Light Green/Black wire at LDP harness connector. If LEAK DETECT SW state does not change, go to next step. If LEAK DETECT SW state changes, replace LDP.
  4. Turn ignition off. Disconnect PCM connectors. PCM is located on left side of engine compartment, between Power Distribution Center (PDC) and Transmission Control Module (TCM). See Figure. Inspect connectors for damaged pins, corrosion and loose terminals. Repair connector as necessary. If connectors are okay, measure resistance of Orange/Red wire between LDP harness connector and terminal No. 72 at PCM C2 harness connector. See Figure. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Orange/Red wire.
  5. Measure resistance between ground and terminal No. 72 (Orange/Red wire) at PCM C3 harness connector. If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, repair short to ground in Orange/Red wire between LDP and PCM.
  6. At this time PCM is assumed to be defective. Replace PCM.
  7. At this time, conditions for DTC to set do not exist or fault is an intermittent problem. Using scan tool, read and record FREEZE FRAME data. Road test vehicle under conditions in FREEZE FRAME data, paying particular attention to fault setting conditions such as speed, temperature, load and MAP vacuum. Using scan tool, read DTCs. If GOOD TRIP counter display count changes to "0", go to step  2. If GOOD TRIP counter display does not change to "0", go to next step.
  8. Start engine and allow it to idle. Using scan tool, perform LEAK DETECTION PUMP (LDP) TEST. Using scan tool, monitor LDP switch state while wiggling wiring harness from LDP to PCM. LDP is located on top of fuel tank. See Figure. PCM is located on left side of engine compartment, between Power Distribution Center (PDC) and Transmission Control Module (TCM). See Figure. If LDP switch state stops toggling while wiggling wiring harness, repair wiring harness where wiggling caused toggling to stop. If LDP switch state does not stop toggling while wiggling wiring harness, go to next step.
  9. Turn ignition off. Visually inspect related connectors and wiring harness. Repair connectors and wiring harness as necessary. If connectors and wiring harness are okay, no problem is indicated at this time. Test is complete. Check for any technical service bulletins that may apply.
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