SOLVED: Short-attention span summary: I damaged the C1 connector and this caused the ECM to lose communication over the serial data line. Once I replaced the connector, the truck started.
I bought this truck recently and wanted to dump the clutch fan so I can use an electric one. Doing some reading on the subject, the 2005 E40 ECM allows for either a clutch fan (Rainier/Envoy/Trailblazer etc), discrete (relay) fans (GTO), or a PWM fan (C6 Corvette).
I'll try & attach a pinout comparison I pulled from the service manuals for each (Excel spreadsheet).
What I did was use ECM pin C1-36, which in the Rainier is the fan clutch control wire, and I just unplugged the fan connector. I re-pinned a new wire in the C1-36 opening and taped off the old one. The new wire goes to the new fan's PWM terminal. The wiring diagram shows it goes to a fan relay terminal and it appears to be a +12V feed for the relay's coil- the opposite terminal goes to ground. I do not see a class 2 data connection for the fan clutch. It has a total of 5 wires:
A: Chassis ground
B: Clutch supply voltage (+12V), from above relay
C. Low reference for Hall sensor, goes to ECM
D. Cooling fan speed signal, goes to ECM
E. 5 volt reference to Hall sensor from ECM
I have attached the cooling schematic as a PDF.
On the C6, C1-36 is the PWM output or fan speed control.
The fan is out of a Mercedes and I verified it operates with the same PWM settings as the C6 by using a PWM generator. It's a really simple setup, 2x heavy gauge power & ground, and a small gauge wire for the PWM.
I reflashed the calibration using the fan settings for the C6. The truck will no longer start. I reflashed the stock calibration, and also did a write entire trying both. Same problem remains. I pulled the battery (both cables) for a few hours and left the headlights on to draw out any holdover power. No change.
I sent in a ticket via HP Tuners and no one could figure out what happened, but they said the ECM seems to be OK. There is an older thread where the BCM in a 2007 Tahoe went out after a Gen 4 ECM reflash. My symptoms are very similar. In that instance, the member put in a new BCM, flashed it, and his truck started. He reported no communication withe BCM via his Tech 2 tool.
A generic code scanner gave me two ECM DTC codes, loss of communication with the BCM or U1064. There was also a loss of comm with the climate control, U1152.
Where I'm at now is trying to get one of the VCX Nano Tech 2 adapters (Tech2Win) to work with my laptop, truck, and the Delco SPS site so I can program modules. I bought a programming subscription, but it gives me an error when I try to connect to flash modules (that's another battle). Using it as a diagnostic tool, I get a U1000 Class 2 Serial Datalink malfunction error on most modules. The odd thing is the BCM responds to all inputs such as headlight switch position, so unlike the member with the 2007 Tahoe, I can communicate with the BCM. I can also ping all modules. I'm going to try a new BCM as soon as I can get my adapter to connect to GM's SPS.
This is worse than trying to put a Chevy V8 into a BMW!!!
2005 E40 Pinouts Rainier-C6-GTO.xlsx
2005_Rainier_cooling_circuits.pdf