Test Dg - Knock Sensor (KS)

NOTE: Perform this test when 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 and DYNAMIC RESPONSE CHECK.

Fig 1: Knock Sensor Circuits

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

Poor fuel quality
Engine mechanical condition
Spark timing

1) Code 25: Generate Knock Signal Manually Code 25 indicates that the Knock Sensor (KS) signal was not received by the ECA during the dynamic response (Goose) test after the engine ID code in the KOER Self-Test. Possible causes for this fault are:

Faulty knock sensor
Open or shorted harness
Faulty ECA

Have 4 oz. hammer ready. Ensure engine is at normal operating temperature. Perform KOER Self-Test. Immediately after DYNAMIC RESPONSE CHECK request 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) Check KS Circuit Voltage 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 between KS circuit and SIG RTN at sensor vehicle harness connector. If reading is greater than 4 volts, go to step 5). If reading is 1-4 volts, go to step 6). If reading is less than one volt, go to next step.

3) Check Continuity of KS & SIG RTN Circuits 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 SIG RTN circuit at KS harness connector and test pin No. 46. Measure resistance between KS circuit at the vehicle harness connector 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) Check 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 200-k/ohm scale. Measure resistance between test pin No. 23 and test pins No. 40, 46 and 60. If all readings are 10 k/ohms or more, remove breakout box, reconnect ECA and go to step 6). If any reading is less than 10 k/ohms, repair shorts in harness and repeat QUICK TEST.

5) Check KS Circuit for Short to Voltage Turn key off and wait 10 seconds. With breakout box installed, ECA and KS 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, remove breakout box, reconnect ECA and go to next step.

6) Test ECA With Substitute Knock Sensor Turn key off and wait 10 seconds. Remove breakout box and reconnect ECA. Connect substitute knock sensor into harness but do not install sensor on engine. Substitute sensor 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.