Questions and Answers

Toyota Knocked Up Q. I have a 1990 Toyota 4X4 V6 SR5 pickup, with 115,000 miles and it is in great shape. Last year my check engine light came on and I discovered 2 codes: 2-1 O2 sensor and a 5-2 knock sensor. I brought it to a garage and they replaced the O2 sensor, and the check engine light never came on again... until this weekend!

I checked the code and it is the 5-2. I have done some testing which I will explain, all testing is with the computer reset. While parked and the vehicle idling the check engine light will not come on, but if I rev the motor to about 3000 RPM and hold it for about 25 seconds the light will appear. Or under normal driving conditions, approximately 25 seconds into the drive the light will come on.

Initially I thought that the knock sensor might be bad or that I had an open condition, but after completing the above test I am rethinking that philosophy. It seems like the sensor is working, or maybe it takes 25-30 seconds of running time before the sensor trips the computer.

I have also thought that I may need to upgrade my gasoline quality. I usually put in 87. The day the sensor came on my tank was down close to EMPTY, so maybe I have some engine knock.

Any advice you can give me would be greatly appreciated. I called the Toyota dealership and they are more concerned about getting my money than helping me out. I have considered the idea of getting a diagnostic test done at the Toyota dealership, but when I ask them about it they are so vague about what the test tells them. From what I can tell for $60 at a dealership, I can do for nothing at my house by jumping a couple wires and finding the fault code.

Boy I hope you know what is going on!

Thanks,

A. Okay, first let's talk about what the Knock Sensor is. This sensor is mounted on the engine block and monitors ignition knock (Detonation). This signal is sent to the ECU which in turn retards the ignition timing until detonation ceases. This control prevents internal damage to engine valves and pistons. The Knock Sensor inputs the ECU through terminal KNK.

To test the sensor:

1. Warm-up engine to normal operating temperature.
2. Attach a timing light with advance indicator and a tachometer. Locate the Knock Control Sensor, (on the top, center of the engine block), and ensure that the connector is secure.
3. While operating the engine at 2,000 rpm, check the ignition spark advance and calibrate the timing mark to 00TDC.
4. Using a wrench or small hammer, tap the exhaust manifold and observe the timing marks.
5. The ignition timing mark should move in the retard direction, depending on the intensity and speed of the tapping.
6. If the timing mark does not retard, turn the engine off and check the wiring between the Knock Control Sensor and the ECU.
7. If no problems are found, replace the Knock Control Sensor and repeat test procedure.
8. If timing still does not retard, replace the ECU.

Since there are only three conditions that will turn the light on, an open in the knock sensor circuit, a bad knock sensor or bad ECU, this test will pinpoint exactly what the cause is.

Additional Information provided courtesy of ALLDATA