Knock Sensor Circuit Continuity Check

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Nov 21, 2010
San Diego, CA
I have been getting intermittent ec55 when pushing my 'ol dog (fj80 '93 with 300k+) pretty hard and it then retards timing and I get a loss of power. This is the rear knock sensor which I replaced years ago and spliced the wire. There has been no issues until the last couple of months. I took the sensor out and ensured that there was not continuity from the wire tab to the body of the sensor. (Hayne's recommended check for sensor integrity.)

I thought I would check the circuit from the sensor plug to the ECU (pin 14 on the 16 pin connector). I removed the ECU and pulled its plugs. I don't get continuity. As a sanity check I then decided to check the front knock sensor's circuit to the ECU (pin 6 on the 16 pin connector) - no continuity. Should I be able to check the integrity of the circuit like this? I thought I was being clever, but now it seems not so much. Thoughts? Thanks!

BTW, I am using a diagram that says it is for 1995-1996 1fz-fe ECU. My ECU says 1fz-fe on it. Additionally, the Haynes manual electric diagram indicates a 6 on the ECU for knock1 and a 14 for knock2. This is an encouraging cross check. Hopefully compatible.

Actually, I double-checked and I do have continuity from the back knock sensor plug to the 14th location on the ECU 16 pin plug. This leaves me at a bit of a loss for the intermittent throwing of the 55 code and the timing retardation. Any ideas what else I could check?

A 26 was also thrown this last time, but I am thinking that is probably a result of the timing retardation and the increase in fuel richness that comes with the 55.

What else could cause the 55 to get thrown?

- it is not actually knocking when this happens
- I am often pushing the truck hard, like passing uphill at high speed
- when the car is turned off and back on, the timing is back to normal

Thanks in advance for any thoughts.
Oh and I did check from the sensor plug across the wiring splice I had made a few years ago. It has continuity.

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