Random "Communication Link Error"

[Repeatman]

Where to begin. 1998 Chevy Tahoe LS. So I took my Tahoe in for an emissions test a few days ago. They could not "Pass" It or "Fail" it because while it was on a dyno, the ecm would randomly stop communicating with Their Computer. Like as if Someone turned the Key off. But the engine would still run smooth and the transmission would still shift fine. I decided to go to the Junk Yard and pick up a used ECU and install it. Well, I got it working on the truck but, The problem still there. If The truck is sitting Idling It would talk to my scan tool just fine. As soon as I start driving ( up to highway speed) It just randomly stops communicating with my scan tool for no reason. I checked the following

1. Fuses

2. Connections on the ECU

3. Wiring Harnesses

4. wiggled my OBD2 Scan Tool Connection while hooked up, The problem would not present itself

5. screamed a few cuss words

So, If anyone has any Input on this Feel free. Also, I found out I will need to reinstall the Other ECM and have it Reprogramed with the Correct Mileage.

 

[M1Gunner]

I would double check the harness to include the connector terminals. Everything works fine sitting still but once driving it’s intermittent. That’s where I would begin. Just to cross your t’s And dot your I’s. The terminals are known for coming loose and also check for any green crustiest that may be hiding inside the connector hiding a broken terminal. You’ll need to hit it with a fine tooth comb, figuratively speaking of course.

 

[Repeatman]

So, The answer to my problem literally came driving up my driveway this morning. My Brother in law owns a 1998 Chevy Silverado K1500 with a 5.7L V8. He stopped by and told me his check engine light is on and if I could quickly pull the codes. I did that, The code was a P0137 O2 Sensor Circuit Low Voltage Bank 1 Sensor 2. I decided to view live data and start the truck and then something similar happened as to what is happening on my Tahoe. I got the Random "Communication Link Error" message but like every 5 seconds. I was able to view and verify that the O2 sensor voltage was low by simply hitting "Try again" a million times and sure enough got 0.010 volts on the sensor while Idle. So, I reinstalled my Original ECM started and ran the engine, hooked up my OBD2 scan tool and looked at my O2 Sensors, sure enough, on Bank 2 Sensor 2 on my Tahoe the Voltage would randomly go down to 0.010 after a minute of Idling and guess what? "Communication link Error" popped up on my screen. I did test my scan Tool on my other car and while viewing Live data it worked flawlessly. So, Would a malfunctioning sensor cause this? Even if I cold start my truck and drive it, I get "Communication link Error" Constantly. Or is there something else that needs to be looked at? This is so weird.

 

[M1Gunner]

So, The answer to my problem literally came driving up my driveway this morning. My Brother in law owns a 1998 Chevy Silverado K1500 with a 5.7L V8. He stopped by and told me his check engine light is on and if I could quickly pull the codes. I did that, The code was a P0137 O2 Sensor Circuit Low Voltage Bank 1 Sensor 2. I decided to view live data and start the truck and then something similar happened as to what is happening on my Tahoe. I got the Random "Communication Link Error" message but like every 5 seconds. I was able to view and verify that the O2 sensor voltage was low by simply hitting "Try again" a million times and sure enough got 0.010 volts on the sensor while Idle. So, I reinstalled my Original ECM started and ran the engine, hooked up my OBD2 scan tool and looked at my O2 Sensors, sure enough, on Bank 2 Sensor 2 on my Tahoe the Voltage would randomly go down to 0.010 after a minute of Idling and guess what? "Communication link Error" popped up on my screen. I did test my scan Tool on my other car and while viewing Live data it worked flawlessly. So, Would a malfunctioning sensor cause this? Even if I cold start my truck and drive it, I get "Communication link Error" Constantly. Or is there something else that needs to be looked at? This is so weird.

Nope, absolutely not. The 0.010 volt is a ghost voltage that’s exactly that, a ghost voltage. It’s not there. A bad oxygen sensor would not cause this issue and if you think it would, you could always disconnect the sensor and play trial and error. Now the root cause may have something in common with that sensor, that’s a possibility. The sensor itself, I’ve seen some strange things but it’s gonna be a hard no for me.

 

[Repeatman]

Alright, I found the problem, The Alternator was spiking and Fluctuation extremely bad while running. I changed it out with a 105 amp stock alt and problem solved. Passed Smog 2 days ago.