Diagnostic Aids

The PSP switch is a normally closed switch that opens as pressure in the power steering system increases.

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 Code 52/519 is displayed, check if vehicle is equipped with power steering. If vehicle is not equipped with power steering, disregard code.

This test is only intended to diagnose:

• Power Steering Pressure (PSP) switch.
• PSP and SIG RTN wiring harness circuits.
• Powertrain Control Module (PCM).

To prevent replacement of good components, be aware the following non-EEC related areas may be at fault:

• Idle speed/throttle stop adjustment.
• Binding throttle shaft/linkage.
• Cruise control linkage.
• Power steering hydraulic system.

Fig 1: Power Steering Pressure (PSP) Switch Circuit

1. 1) KOEO Code 52/519: Attempt To Eliminate Code  Code 52/519 indicates PSP switch circuit is open. Possible causes for this fault are:
   • Damaged PSP switch.
   • Open circuit in wiring harness.
   • Faulty PCM.

   Turn ignition off. Disconnect PSP switch. Install jumper wire between PSP terminal and SIG RTN terminal at wiring harness connector. Repeat KOEO SELF-TEST. If Code 52/519 is not displayed, replace PSP switch and repeat QUICK TEST. If Code 52/519 is displayed, remove jumper wire and go to step 2).

2. 2) Check Continuity Of PSP Circuits  Turn ignition off, and wait 10 seconds. Disconnect PCM 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 46 and SIG RTN terminal at PSP switch wiring harness connector. Also measure resistance between test pin No. 24 at breakout box and PSP terminal at switch wiring harness connector. If both readings are less than 5 ohms, replace PCM and repeat QUICK TEST. If readings are 5 ohms or more, repair open circuit and repeat QUICK TEST.
3. 3) Check PSP Switch Operation  Turn ignition off. Connect tachometer, and start engine. Allow engine to idle with transmission in Park or Neutral. Disconnect PSP switch wiring harness connector. If RPM increases, replace PSP switch and recheck system. If RPM does not increase, go to step 4).
4. 4) Check PSP Switch Circuits For Shorts  Turn ignition off. Disconnect PSP switch wiring harness connector. Disconnect PCM 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pins No. 24 and 46 at breakout box. If resistance is 10,000 ohms or less, repair short in harness and recheck symptom. If reading is more than 10,000 ohms, replace PCM and recheck symptom.
5. 5) KOER Code 52/521  Disregard this code if vehicle does not have power steering. Code 52/521 indicates PSP switch did not change states due to open or closed switch. Possible causes for this fault are:
   • Damaged PSP switch.
   • Open or shorted circuit in wiring harness.
   • Front wheels turned but not centered.
   • Faulty PCM.

   If steering wheel was turned 1/2 turn within 2 seconds after engine ID code and then returned to center, go to step 6). If steering wheel was not turned, repeat QUICK TEST.

6. 6) Check PCM Open Circuit Identifying Capabilities  Turn ignition off. Disconnect PSP switch. Perform KOEO SELF-TEST. If Code 52/519 is present, go to step 8). If Code 52/519 is not present, go to step 7).
7. 7) Check PSP Switch Circuits For Shorts  Turn ignition off. Disconnect PSP switch. Disconnect PCM 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pins No. 24 and 46 at breakout box. If reading is 10,000 ohms or less, repair short circuit and repeat QUICK TEST. If reading is more than 10,000 ohms, replace PCM and repeat QUICK TEST.
8. 8) Check PSP Switch Position Comparison  Turn ignition off. With PSP switch connected, turn ignition on. Measure resistance between test pins No. 24 and 46 at breakout box. Start engine. Measure resistance between test pins No. 24 and 46 at breakout box. If reading shows less than 10 ohms difference between key on engine off and key on engine running, go to step 9). If reading is not as described, replace PSP switch and repeat QUICK TEST.
9. 9) Check PSP Switch With Engine Running (Load & No Load)  Connect PSP switch. Start engine, and allow it to idle. Measure resistance between test pins No. 24 and 46 at breakout box. Turn steering wheel 1/2 turn and return to center position. If resistance changes from less than 10 ohms to infinity and then returns to 10 ohms or less (when steering wheel is centered), PSP switch system is okay. Testing is complete. If reading does not change as indicated, replace PSP switch. Repeat QUICK TEST.
10. 10) Code 519: Attempt To Eliminate Code 519  Disregard this code if vehicle does not have power steering. Code 519 indicates PSP switch circuit is open. Possible causes for this fault are:
    • Damaged PSP switch.
    • Open or shorted circuit in wiring harness.
    • Front wheels turned but not centered.
    • Faulty PCM.

    Turn ignition off. Disconnect PSP switch connector. Repeat KOEO SELF-TEST. Measure resistance between test pins No. 24 and 46 at breakout box. If Code 519 is not present, replace PSP switch. If Code 519 is present, go to step 11).

11. 11) Check PSP Circuit For Short  Turn ignition off. Disconnect PCM 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pins No. 24 and 46 at breakout box. If reading is 10,000 ohms or less, repair short circuit and repeat QUICK TEST. If reading is more than 10,000 ohms, replace PCM and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 11) to step 15). No test procedures have been omitted.
12. 15) Check PSP Switch Operation  Connect tachometer, and start engine. Allow engine to idle in Park or Neutral. Disconnect PSP switch connector. Using jumper wire, connect PSP switch wiring harness connector terminals. If RPM increases, replace PSP switch and recheck system. If RPM does not increase, go to step 16).
13. 16) Check Continuity Of PSP Switch Circuits  Turn ignition off, and wait 10 seconds. Disconnect PCM 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM connected. Measure resistance between test pin No. 46 and SIG RTN terminal at PSP switch wiring harness connector. Also measure resistance between test pin No. 24 at breakout box and PSP terminal at PSP switch wiring harness connector. If both readings are less than 5 ohms, replace PCM and repeat QUICK TEST. If any reading is 5 ohms or more, repair open circuit and repeat QUICK TEST.
    NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 16) to step 20). No test procedures have been omitted.
14. 20) KOER Code 521  Disregard this code if vehicle does not have power steering. Code 521 indicates PSP switch did not change states due to open or closed switch. Possible causes for this fault are:
    • Damaged PSP switch.
    • Open or shorted circuit in wiring harness.
    • Front wheels turned but not centered.
    • Faulty PCM.

    If steering wheel was turned 1/2 turn within 2 seconds after engine ID code and then returned to center, go to step 21). If steering wheel was not turned, repeat QUICK TEST.

15. 21) Check PCM Closed Circuit Identifying Capabilities  Turn ignition off. Disconnect PSP switch. Connect jumper wire between PSP terminal and SIG RTN terminal at PSP switch wiring harness connector. Perform KOEO SELF-TEST. If Code 519 is present, remove jumper wire and go to step 23). If Code 519 is not present, go to step 22).
16. 22) Check Continuity Of PSP Switch Circuits  Turn ignition off, and wait 10 seconds. Disconnect PCM 60-pin connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 24 at breakout box and PSP terminal at PSP switch wiring harness connector. Also measure resistance between test pin No. 46 at breakout box and SIG RTN terminal at PSP switch wiring harness connector. If both readings are less than 5 ohms, replace PCM and repeat QUICK TEST. If either reading is 5 ohms or more, repair open circuit and repeat QUICK TEST.
17. 23) Check PSP Switch Position Comparison  Turn ignition off. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM connected. Reconnect PSP switch. Turn ignition on. Measure resistance between test pin No. 24 and test pin No. 46 at breakout box. Start engine. If reading shows less than 10 ohms difference between key on engine off and key on engine running, go to step 24). If reading is not as described, replace PSP switch and repeat QUICK TEST.
18. 24) Check PSP Switch With Engine Running (Load & No Load)  Start engine, and allow it to idle. Measure resistance between test pin No. 24 and test pin No. 46 at breakout box. Turn steering wheel 1/2 turn and return to center position. If resistance changes from less than 30 ohms to infinity and then returns to 30 ohms or less (when steering wheel is centered), PSP switch system is okay. Testing is complete. If reading does not change as indicated, replace PSP switch. Repeat QUICK TEST.