Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Explorer and 1995 Ford Aerostar. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test if directed by QUICK TEST or other diagnostic tests. This test is intended to diagnose:

Knock sensor.
Wiring harness circuits (KS and SIG RTN).
Powertrain Control Module (PCM).

To prevent replacement of good components, be aware the 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 (4.0L)

TEST PIN NO. 23 (KS) WIRE COLOR IDENTIFICATION

Application	Wire Color
All Models	Yellow/Red

TEST PIN NO. 46 (SIG RTN) WIRE COLOR IDENTIFICATION

Application	Wire Color
All Models	Gray/Red

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

Faulty Knock Sensor (KS).
Open or shorted harness.
Faulty PCM.

Disconnect PCM 60-pin connector. Inspect connector terminals for damage and repair as necessary. Install Breakout Box (T83L-50-EEC-IV), leaving PCM connected. Turn ignition on. Measure DC voltage between test pins No. 23 and 46 at breakout box. If DC voltage is 2.4-2.6 volts, go to next step. If DC voltage is less than 2.4 volts, go to step 4). If DC voltage is more than 2.6 volts, go to step 5).

2) Check KS Voltage Increase Start engine. Leave DVOM test leads connected to test pins No. 23 and 46. Monitor AC voltage at idle and at 3000 RPM. If AC voltage increases, replace PCM and repeat QUICK TEST. If AC voltage does not increase, go to next step.

3) Check Continuity Of Knock Sensor (KS) & SIG RTN Circuits Turn ignition off. Disconnect KS wiring harness connector. 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 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 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, replace knock sensor and repeat QUICK TEST. If Code 225 is still present, replace PCM. If any reading is less than 10,000 ohms, repair short circuit and repeat QUICK TEST.

5) Check KS Circuit For Short To Voltage Ensure PCM and KS are disconnected. Turn ignition on. Measure DC voltage between test pins No. 23 and 40. If reading is 0.5 volt or more, repair short circuit in wiring harness and repeat QUICK TEST. If reading is less than 0.5 volt, replace PCM and repeat QUICK TEST.