02 TB multiple electrical issues

Ok, here's the story with this one. Truck came in because the fan was running full speed all the time. Customer had already replaced the fan clutch assembly with new OEM unit and it didnt fix anything. Has code for no fan speed sensor signal. Also, the IAT sensor is reading -40 deg and had (had, not has) a code for the IAT sensor circuit being open. Customer also changed that sensor (didnt fix it of course). When the truck came in the code for the IAT was gone, but it still read -40 on the diagnostic tool. The truck also now had a code for the AC high pressure switch being open or shorted. The fan sensor code also remained. I checked the wiring for the fan and found that the 5v supply was showing no voltage at the fan clutch connector, but a full 5 volts where it leaves the ECU connector. Didnt get to unwrap the wiring harness to fully expose the wire (it's buried) but from what I can see it hasnt been tampered with or visually cut. I had to pull the truck out to get another car in, and when I went to pull the truck back in, I backed it up out of the space, and when I put it in drive it died. All the lights come on, but it wont start (no click, nothing). Antitheft system says the key code is OK! I checked the starter with a jumper lead and it cranks if you put 12v to the starter solenoid activation terminal, but even with the key on it wont start and run. The only help the customer could provide was that a few weeks ago he spilled a soda on the back seat. I understand the BCM and a fuse box are back there, but I dont see any signs that anything got into them. I checked the ECU connector for corrosion or loose terminals with no luck, same with all the sensor connectors that were involved. Also checked he quick release plug by the main fuse box (cause it was right there..). Battery has a full charge and good connections. Anyone have any insight? :banghead:

Got a starter relay in the underhood fuse panel, start checking the relay and circuits from there. Open circuit some where for iat sensor if it read -40. Ignition switches were problematic on the truck also, you may a passkey issue . No am alarm/cutoff, right? Can you scan the bcm?

Prob won't help, but have the same prob with my 02tb for over 3 wks now. Was going boating, started engine, loaded a couple things into the back seat, shut off motor to check the oil since I just had to replace the engine at 83k (and the 4wd at 27k and on and on) so still breaking in engine. Oil was fine, closed the hood, jumped in, and nothing, nada. Lights came on, left headlight was dim to about 30%, all lights on dash on, some dim, but no crank. My mech came up with a batt, no luck. He towed to his shop, had it now for 3 wks, nothing. There is a chev tsb 3577 (no crank, no start, no codes), but I do not have access to them, so not sure it will help anyway. The dim headlight is wierd, replaced it, did not help, replaced starter, no help, pulled headlight assembly, no help, checked all fuses and relays, no help, did clear the security passlock with the procedure chev applies, no help, no codes on the obd, have used 4 diff code readers from cheap to 5k, no help, no codes. No moisture on back seat above rear fuse block. Starter relay ok. Pos to neg cable ohm check ok. Locksmith said keyset ok. This is nuts.:screwy: The last 2 trips to the dealer, well 3 with the 4wd, were so frustrating and expensive (> $5000) that I refuse to go there. This is undoubtedly the worst car I have ever owned in my 60 yrs. Chevy corporate has blown me off. I just made my final payment 2 days ago, ain't that ironic? I will take any suggestions in addition to the ones the moderator had and appreciate it very much. Ditto on the :banghead: . OH, the mech said the starter was fried, not mechanical, but electrical. He was told my another mech that it sounded like it grounded out thru the starter, whatever that means. I did not hear any noise when I last started it. We did have a 24hr heavy rain the day before. Something damp? Not for 3 weeks.