Is your voltmeter accurate? Are you on the right scale? At least 10K ohms input impedance? (More than 10K is OK, even preferable.)Also, i tried measuring the voltage from the HARNESS to Ground and it reads 1.48V. According to the flowchart either an open ground or i need a new ECM... i checked the ground and its good.
I haven't seen any threads on this site end with replacing the ECM, so you can see my skepticism.
1. That chart is for a carbureted Spectrum. You have a fuel-injected V-8 pickup truck. No promises that the chart is accurate for your vehicle. Get a REAL service manual for YOUR vehicle.Here is the AllData diagnostic flowchart for DTC 13.
I've followed the chart and i end at "OPEN CKT 413, FAULTY ECM CONNECTION OR ECM over 0.6v [1.5v]"
There must be some reason the ECM is sending 1.5v to the O2 sensor, or at least it must be some clue for whats going on.
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2. HOW are you checking the voltage? Chart says to disconnect the O2 sensor, jumper the harness side to ground, start engine, and look at the O2 voltage on a scan tool. Should be less than 0.2 volts. IS IT?
What is the scan tool showing for O2 voltage with the sensor connected normally as you drive?
Maybe you have a positive-backpressure EGR valve, and with no catalyst, it doesn't have any backpressure to make it work like it was engineered to.EGR has been replaced with new factory-grade parts.