DTC P1494: LEAK DETECTION PUMP SW OR MECH FAULT Dodge Ram Van B2500

Note. For connector terminal identification, see CONNECTOR IDENTIFICATION . For circuit identification and wiring diagram, see RAM VAN & RAM WAGON wiring diagram in WIRING DIAGRAMS article.

Note. DTC P1494: LEAK DETECTION PUMP SW OR MECH FAULT is monitored immediately after a cold start, with ambient temperature 40 -90°F (4.4-32.2°C) and engine coolant temperature within 10°F (-12.2°C) of ambient temperature. DTC may be stored in Powertrain Control Module (PCM) when PCM senses state of Leak Detection Pump (LDP) switch is not in expected state at ignition on, with engine off, or following an engine start if a change in switch state is not sensed when LDP solenoid is energized to pull LDP diaphragm to up position. Possible causes are: defective LDP, defective PCM, defective connectors or defective wiring.

1. Turn ignition on, with engine off. Using scan tool, read DTCs. If DTC SPECIFIC GOOD TRIP COUNTER is displayed and displayed count is "0", go to step 4). If DTC SPECIFIC GOOD TRIP COUNTER is not displayed or displayed count is not "0", go to next step.
2. Determine if DTC matches FREEZE FRAME DTC. If DTC is equal to FREEZE FRAME DTC, go to next step. If DTC is not equal to FREEZE FRAME DTC, repair DTC using FREEZE FRAME data.
3. Using scan tool, read and record FREEZE FRAME data. Road test vehicle to try to duplicate FREEZE FRAME data conditions. If DTC SPECIFIC GOOD TRIP COUNTER is displayed and displayed count is "0", go to next step. If DTC SPECIFIC GOOD TRIP COUNTER is not displayed or displayed count is not "0", go to step 10).
4. Turn ignition off. Disconnect LDP connector. Disconnect engine vacuum supply hose at LDP. LDP is located on a bracket mounted to right front inner fender, near battery. Clean and/or repair connector as necessary. Turn ignition on, with engine off. Using a voltmeter, check voltage on ASD relay connector, fused ignition switch output circuit (Light Green/Black wire). ASD relay is located in Power Distribution Center (PDC). PDC is located next to battery. Refer to label under PDC cover for relay location. If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open fused ignition switch output circuit. Perform TEST VER-5A. NOTE: LDP pressure switch sense circuit may also be referred to as LDP switch sense circuit.
5. Turn ignition off. Ensure LDP connector and vacuum hose are still disconnected. Disconnect PCM connectors. PCM is located in engine compartment. See PCM LOCATION table under SYSTEM DIAGNOSTICS. Clean and/or repair connectors as necessary. Using an ohmmeter, check resistance between ground and PCM connector, LDP pressure switch sense circuit (Orange wire). If resistance is less than 5 ohms, repair LDP pressure switch sense circuit for short to ground. Perform TEST VER-5A. If resistance is 5 ohms or more, go to next step.
6. Ensure ignition is off. Ensure LDP connector and vacuum hose are still disconnected. Ensure PCM connectors are still disconnected. Using ohmmeter, check resistance of LDP pressure switch sense circuit (Orange wire) between LDP and PCM. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open LDP pressure switch sense circuit. Perform TEST VER-5A.
7. Ensure ignition is off. Reconnect LDP connector. Ensure vacuum hose is still disconnected. Ensure PCM connectors are still disconnected. Connect a jumper wire between ground and PCM connector, LDP solenoid control circuit (White/Dark Green wire). Turn ignition on, with engine off. Connect a hand-held vacuum pump to LDP. Using a voltmeter, monitor voltage on PCM connector, LDP pressure switch sense circuit (Orange wire) while applying vacuum to LDP. If voltage changes when vacuum is applied, go to next step. If voltage does not change when vacuum is applied, replace LDP. Perform TEST VER-5A.
8. Turn ignition off. Disconnect LDP connector. Ensure vacuum hose are still disconnected. Ensure PCM connectors are still disconnected. Connect a vacuum gauge between engine vacuum supply hose and LDP. Start engine and allow it to idle. Read vacuum gauge. If vacuum gauge reads within one in. Hg of engine vacuum, go to next step. If vacuum gauge does not read within one in. Hg of engine vacuum, repair leak or obstruction in engine vacuum supply hose. Perform TEST VER-5A.
9. At this time PCM is assumed to be defective. Replace PCM. Perform TEST VER-5A.
10. Turn ignition off. Visually inspect related connectors and wiring harness. Repair connectors and wiring harness as necessary. Perform TEST VER-5A. If connectors and wiring harness are okay, go to next step.
11. Start engine and allow it to idle. Using scan tool, go to LEAK DETECTION PUMP TEST. Select LDP SWITCH TEST. While monitoring LDP switch state, wiggle wiring harness from LDP to PCM. If LDP switch state does not stop toggling while wiggling wiring harness, test is complete. If LDP switch state stops toggling while wiggling wiring harness, repair wiring harness where wiggling caused toggling to stop. Perform TEST VER-5A.