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Circuit Test B7

NOTE: Perform this test when Service Code 25 is received during QUICK TEST procedure or you are directed here by other diagnostic tests. Use DYNAMIC RESPONSE CHECK as specified in steps 1) and 6). There is no need to perform WOT during this test. For additional information see QUICK TEST DIAGNOSTIC AIDS, DYNAMIC RESPONSE CHECK in front of this article.
Fig 1: Knock (Detonation) Sensor Circuit
G54778

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: fuel quality, engine condition (valves, vacuum leaks, valve timing, EGR valve, etc.) and spark timing.

  1. Code 25: Generate Knock Manually. Code 25 indicates that the Knock Sensor (KS) signal was not sensed during the dynamic response ("Goose") test after the engine ID code in the KOER SELF-TEST. Possible causes for this fault are a faulty KS, open or shorted harness or faulty ECA. Have 4 oz. hammer ready. Ensure engine is at normal operating temperature. Perform KOER SELF-TEST. When DYNAMIC RESPONSE CHECK signal appears, lightly tap above knock sensor with 4 oz. hammer. DO NOT  "Goose" throttle. After 15 seconds, check for Code 25. Ignore all other codes at this time. If code 25 is displayed, go to next step. If Code 25 is not displayed, knock system is okay. Repeat KOER SELF-TEST and service other codes.
  2. Circuit Voltage Check. Turn key off and wait 10 seconds. Disconnect knock sensor. Inspect for and repair any damaged wiring. Set DVOM on 20-volt scale. With KOEO measure voltage at knock sensor connector between KS and SIGNAL RETURN. If reading is greater than 4 volts, go to step 5). If voltage is 1-4 volts, go to step 6). If reading is less than one volt, go to next step.
  3. Check Continuity of KS and Signal Return Circuit. Turn key off and wait 10 seconds. Disconnect ECA 60-pin connector. Inspect for and repair any damaged wiring. Install breakout box, leaving ECA and knock sensor disconnected. With DVOM on 200-ohm scale, measure resistance between SIGNAL RETURN at sensor harness connector and test pin No. 46, and between knock sensor connector KS signal and test pin No. 23. If either reading is 5 ohms or more, service open circuit and repeat QUICK TEST. If both readings are less than 5 ohms, go to next step.
  4. Checking KS Circuit for Short to Ground. Turn key off and wait 10 seconds. With breakout box installed, ECA and knock sensor disconnected, set DVOM on 200K-ohm scale. Measure resistance between knock sensor connector KS signal and test pins No. 40, 46 and 60. If all readings are 10K ohms or more, go to step 6). If any reading is less than 10K ohms, repair shorts in harness and repeat QUICK TEST.
  5. Checking KS Circuit for Short to Power. Turn key off and wait 10 seconds. With breakout box installed, ECA and sensor disconnected, set DVOM on 20-volt scale. Turn key on, leaving engine off. Measure voltage between test pins No. 23 and 40. If reading is 0.5 volt or more, repair knock sensor harness short to power, and repeat QUICK TEST. If reading is less than 0.5 volt, go to next step.
  6. Test ECA By Sensor Substitution. Turn key off and wait 10 seconds. Remove breakout box and connect ECA. Connect substitute knock sensor into harness but do not install in engine. Substitute should be a known good unit with the same part number. Ensure engine is at normal operating temperature. Perform KOER SELF-TEST. When DYNAMIC RESPONSE CHECK signal appears, lightly tap knock sensor with 4 oz. hammer. DO NOT  "Goose" throttle. If Code 25 is displayed replace ECA, reconnect original knock sensor and rerun QUICK TEST. Ignore all other codes at this time. If Code 25 does not appear, install new knock sensor and repeat QUICK TEST.
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