Diagnostic Aids

Perform this test when Code 25/225 is retrieved during QUICK TEST  procedure or if directed by other diagnostic tests. This test is intended to diagnose:

• Knock sensor.
• Wiring harness circuits (KS and SIG RTN).
• ECA.

To prevent replacement of good components, be aware following non-EEC related areas may be cause of problem:

• Poor fuel quality.
• Engine mechanical condition.
• Ignition timing.

Fig 1: Knock Sensor Circuits & Connector Terminal ID

1) Code 25/225: Generate Knock Signal Manually  Code 25/225 indicates Knock Sensor (KS) signal was not received by ECA during dynamic response (goose) check in KOER SELF-TEST. Possible causes for this fault are:

• Faulty Knock Sensor (KS).
• 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 using 4-oz. hammer. DO NOT goose throttle. Check for Code 25/225. Ignore all other codes at this time. If Code 25/225 is not displayed, knock system is okay. Repeat KOER SELF-TEST, and service any other codes. If Code 25/225 is displayed, go to step 2).

2) Check KS Circuit Voltage  Turn ignition off. Disconnect knock sensor. Set DVOM on 20-volt scale. Turn ignition on. Measure voltage between KS and SIG RTN terminals at sensor wiring harness connector. If reading is less than one volt, go to step 3). If voltage is 4 volts or more, go to step 5). If reading is 1-4 volts, go to step 6).

3) Check Continuity Of KS & SIG RTN Circuits  Turn ignition off, and disconnect ECA 60-pin connector. Install EEC-IV Breakout Box(T83L-50-EEC-IV), leaving ECA and knock sensor disconnected. Measure resistance between SIG RTN terminal at KS wiring harness connector and test pin No. 46 at breakout box. Measure resistance between KS terminal at wiring harness connector and test pin No. 23 at breakout box. If either reading is 5 ohms or more, repair open circuit. Repeat QUICK TEST  . If both readings are less than 5 ohms, go to step 4).

4) Check KS Circuit For Short To Ground  Turn ignition off. Measure resistance between test pin No. 23 and test pins No. 40, 46 and 60 at breakout box. If all readings are 10,000 ohms or more, remove breakout box. Reconnect ECA, and go to step 6). If any reading is less than 10,000 ohms, repair short circuit. Remove breakout box, and repeat QUICK TEST  .

5) Check KS Circuit For Short To Voltage  Turn ignition on. Measure voltage between test pins No. 23 and 40. If reading is 0.5 volt or more, repair knock sensor harness short to power. Remove breakout box, and repeat QUICK TEST  . If reading is less than 0.5 volt, remove breakout box. Connect ECA, and go to step 6).

6) Test ECA Using Substitute Knock Sensor  Turn ignition off. Connect substitute knock sensor into harness but do not install sensor on engine. Ensure engine is at normal operating temperature. Perform KOER SELF-TEST  . When dynamic response check signal appears, lightly tap knock sensor using 4-oz. hammer. DO NOT goose throttle. If Code 25/225 is displayed, replace ECA. Connect original knock sensor, and repeat QUICK TEST  . If Code 25/225 does not appear, install new knock sensor and repeat QUICK TEST.