Have you checked the other sensors that use the grey 5v wire and ground ? Dont have wiring diagram in front of me.
But IIRC the CPS and 1 other sensor use that power and ground circuit also. Should show them in the shop manual.
With the CTS reading full cold. That will kill your fuel mileage. It may be bad also. There should be a table that gives resistance/temp values for the CTS in the manual.
CPS and MAP are on the 5 volt circuit.
The ECT reading indicates an open circuit, bad ground or bad sensor.
Short the 2 ECT wires and see if you get a high temp reading.
ECT, IAT, MAP, and CPS grounds are spliced in the harness under the intake.
Are the engine grounds at the rear of the pass. side head in good shape?
The grey wire at the CPS and MAP sensor is spliced under the intake and runs to the PCM thru the 8pin connector at the rear of the engine. It is a 5v. feed from the PCM for the CPS and MAP sensors on your 1999.
According to the wiring schematic gm sent me the voltage I detected was at 4.97volts at feed wire, green, the device (map sensor) shows a direct short with resistances across all poles as identical at 1.57 ohms so it spiked the ecm, not certain why it permitted that as the ecm typically has some level of protection, there is a few service info pieces that indicate that I can indeed fault the ecm, and requires replacement
Doubt the sensor damaged the PCM. Normal sensor function is from a very low resistance to a full short.
A short in the wiring harness can cause problems and damage the PCM.
If you think the PCM is bad you could try the PCM from your 96 or get your hands on a PCM from a 97.
96 PCM in a 99 will work except for the WTS light.
97 PCM in a 99 will work perfectly and does not have security. An easy and quick way to narrow down the problem.
98-up PCM will require PASSLOCK reprogramming which makes diagnosis a bigger PITA.
Both battery sets are fully charged, the common denominator is both trucks show service engine indicators, both have under 125k miles, both were exceptional runners, would start in 15 degree weather without block heat, until this
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