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I've been working on a 2005 Tahoe that's starting to drive me up the wall and could use some guidance.

I'll start by saying that this is not my vehicle and I'm not a mechanic; I'm an electrician. I work on my own vehicles and can usually find and solve the issues within a few hours.

The Tahoe started out with a complaint of overheating and over the course of the week I eliminated 3 different coolant leaks and was asked to diagnose a knock sensor. After scanning the truck I pulled up a bunch of codes; they are as follows:

P0332 Knock sensor 2 cct low
P0343 camshaft position sensor cct high voltage
P0446 Evap vent solenoid control system
P0455 Evap system large leak
C0201 ABSenable relay cct open
C0455 steering position sensor cct malfunction
P0101 MAF sensor performance
P0102 MAF sensor cct low frequency
P0171 Fuel Trim system lean bank 1
P0174 Fuel trim system lean bank 2

I ordered in a pair of knock sensors, MAF sensor, and a camshaft position sensor and they were all replaced.

After replacing the sensors It had an even harder time starting than it did before and sometimes will need to be cranked for several seconds and let sit before trying again.
The engine is now also throwing out a P0343 camshaft position sensor high voltage as well as a P0342 camshaft position sensor low voltage at the same time after having replaced the sensor. I have back probed the camshaft sensor wiring at the ECU (and the sensor) and the signal coming back looks fine to me on the oscilloscope; although frankly I can't find anything to actually compare it to.

Top is the CMP and the bottom is the CKP.

I'm leaning toward the ECU having an issue but I'm not 100% and I don't want to have the owner replace it only to have an ongoing issue. I also haven't been able to really drive the truck around but I've had the knock sensor DTC come back as well as a new one that wasn't there before.

P0342 camshaft position sensor cct low voltage
P0343 camshaft position sensor cct high voltage
P0135 Heated oxygen sensor heater performance bank 1 sensor 1
P0332 knock sensor 2 cct low

I pulled the connectors off the back of the ECU and checked the wiring back to the camshaft position sensor and it looks good. There was some corrosion on several pins of the ECU connector 1 though. I cleaned up the pins as best I could and it hasn't made any difference either.

I would love to hear from anyone on what it could be or if you have any diagnostic steps I should take from here.
 

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For starters, get a wiring diagram for your vehicle so you know what connects to what and which wires are which. You might want to get a subscription to ALLDATADIY.COM to find out exactly how to test for the DTC's stored in the computer. Very helpful. Make sure your sensors have a 5 V reference (power), an almost 0 volt low reference. If no 5V reference on the sensors, the ECM is likely the problem. You have a lot of circuit problems, high voltage here, low voltage there. Pick one that is easy to get to for testing. Solve that one. Others may disappear just because of the fix on the first problem.

There are lots of videos on YouTube that show known good waveforms and diagnosis. My favorite is South Main Auto, but there are many more. You will have to sort thru them to find something that looks like it might be similar to your truck's problem - use search within YouTube.
 
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Clean up the braided ground strap from starter area of block to passenger frame.
 
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There is also a ground strap on the back of the driver's side head that goes up to the firewall. You need bare metal to bare metal contact, so use a wire wheel to strip any corrosion or paint off at the ground points. That's the ring terminal, the bolt threads, and the metal it bolts to. Rebolt it back together, then paint over the top of it.

The grounds in any chevy are usually the weak point when it comes to electrical gremlins. The dash grounds are in each kick panel. There is another ground below the driver seat on the frame. All of them are known to corrode, get loose, etc. A quick clean up should only take an hour or so for all 6 main grounds; the 2 kick panels, the under driver seat, the starter, the driver's side head, and the main battery ground at the front crossmember and on the engine.
After you clean them all up you can then start to verify each sensor at the plug is good with the ECM removed. The FSM or alldata has all the values you should be seeing, both for static and during cranking.

I bring up checking it at the ECM with it unplugged as the harnesses can become brittle if you live in a dry, high heat area, or corroded badly if you live in a wet, cold area. Either way, the harnesses can break down and the coating fracture off, causing shorting, intermittent signal breaks, etc. Luckily the engine harnesses are pretty cheap on Ebay.

Your negative spikes in your o-scope square wave should not be there and are indicative of some major interference, either ground path or other.
 
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