94 4runner 3.0 vze engine. I just completed rebuilding it and it is now back in the car and running well. The CEL (Check Engine Light) is on and I have scanned it for the DTC codes. The scanner reads to the codes, but returns that there were no codes in the vehicle ECU. Does anyone have a list of the things to look at when troubleshooting a CEL with no codes?

Thanks for the help.

 

did you check and make sure that all of your electrial connections are hooked up and tight

 

Yes, I have been back through that twice. By using the TE1 to E1 jumper I am getting what I believe to be code 12 and code 52.

Vehicle has a new knock sensor and new wire that routes through the manifold to the wiring harness.

 

I have confirmed that I have codes 12 and 52. I checked the distributor and was getting no reading on the G - NE ohm test. The G - G1 and G - G2 ohm tests returned values of 159 when cold and 185 when warm. The G - NE shows nothing. I then replaced the distributor because the one pick up appeared defective. I tested the distributor before I put it in and all reading were as expected. After installing it and running the engine, I then retested it. The G - NE ohm test no longer showed the appropriate reading. I have traced all 4 wires and tested them for grounds, they don't go to ground and tested them for continuity to the ECU. They all get show continuity. I then tested them to see if they possibly connected to each other, they don't.

What could cause the G - NE resistance to change from running the engine?

 

Now the G - NE resistance is back, it just isn't that hard to test, but sure seems to be a mystery.

Code 52 remains and I have now rewired from connector back to ECU with shielded wire and I still get the 52 Knock Sensor failure to send signal for 6 crank revolutions. It is interesting in that I can test it all I want in the drive way and Check Engine Light doesn't come on. I drive it and it comes on between 1500 rpm and 2200 rpm. I can drive the vehicle 10 or so miles with the engine above 2500 rpm and not get the code. I can idle it in my driveway and not get the code.

I do have one vacuum leak that I am addressing in the intake manifold large tube. Any suggestions would be welcomed.

New knock sensor, new knock sensor cable from knock sensor to connector outside of the intake manifold and new shielded wire from that connection back to the ECU with the shielding grounded near the ECU.