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Diagnostic Aids

Perform this test when instructed during QUICK TEST  or if directed by other test procedures. Some vehicles may not have power steering, but PCM may be equipped with PSP switch software strategy. If a KOEO DTC P1650 or P1651 is displayed, check if vehicle is equipped with power steering. If vehicle is not equipped with power steering, disregard DTC P1650 or P1651. This test is only intended to diagnose:

Fig 1: PSP Test Circuit & Connector Terminals
G95A35964
  1. Step 1) DTC P1650 Or P1651  DTC P1650 indicates PSP signal is out of self-test range. DTC P1651 indicates PSP signal malfunction. Possible causes for this fault are as follows:
    • Open or short in wiring harness.
    • Faulty PSP switch.
    • Faulty PSP switch/shorting bar damage.
    • Faulty Powertrain Control Module (PCM).

    Start engine and allow to idle. Using scan tester, access PSP PID (if scan tester cannot access PSP PID, go to next step). Turn steering wheel left, then right. If scan tester does not indicate on/off switching, go to next step. If scan tester indicates on/off switching, go to CIRCUIT TEST Z.

  2. Step 2) Check PSP Switch Operation  Turn ignition off. Install tachometer. Start engine and allow to idle. Disconnect PSP switch. If engine speed increases when switch is disconnected, replace switch and repeat QUICK TEST . If engine speed does not increase when switch is disconnected, go to next step.
  3. Step 3) Check PSP Switch Operation  Turn ignition off. Install tachometer. Start engine and allow to idle. Disconnect PSP switch. Connect jumper wire between PSP terminal and SIG RTN terminal of connector. If engine speed increases when switch disconnected, replace switch and repeat QUICK TEST . If engine speed does not increase when switch disconnected, see step 4).
  4. Step 4) Check PSP Circuit Continuity  Turn ignition off. Leave PSP switch disconnected. Turn ignition off. Disconnect 104-pin PCM connector. Inspect connector for damage and repair as necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between test pin No. 91 (SIG RTN) at breakout box and SIG RTN terminal of PSP switch connector. If resistance less than 5 ohms, go to next step. If resistance 5 ohms or more, repair open circuit and repeat QUICK TEST .
  5. Step 5) Check For Short In PSP Circuit  Leave ignition off and PSP switch disconnected. Measure resistance between test pin No. 31 (PSP) and 91 at breakout box. Measure resistance between test pin No. 31 and chassis ground. If both resistance measurements are 10,000 ohms or more, go to next step. If resistance is less than 10,000 ohms, repair short circuit and repeat QUICK TEST .
  6. Step 6) Check Switch Resistance  Turn ignition off. Start engine and allow to idle. Disconnect PSP switch. Measure resistance between PSP switch signal and chassis ground while turning steering wheel. If resistance is less than 5 ohms, replace PCM and repeat QUICK TEST. If resistance is 5 ohms or more, replace PSP switch and repeat QUICK TEST .
  7. Step 7) Check Switch Resistance  Turn ignition off. Start engine and allow to idle. Disconnect PSP switch. Measure resistance between PSP switch terminals. If resistance is less than 5 ohms, replace PCM and repeat QUICK TEST. If resistance 5 ohms or more, replace PSP switch and repeat QUICK TEST .
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