"ECU Code Problems on GMC Envoy"

2005 GMC Envoy Rear View

My GMC Envoy was not starting, and I went to diagnose trouble codes. I saw the engine check light on when I attached the device. I didn’t read any codes from the ECU, it’s saying there is no trouble code. I asked my mechanic to unplug the throttle position sensor wire as he unplugged the wire one more engine check light appeared on the dashboard. It was a bit digger in size than the normal engine check light with arrow facing downwards. Why is there two engine check light and what is the reason? Why it can’t be diagnosed through the obd2 reader? I am using elm327 version 1.3a with scan XL.

There are two engine check lights, what are they? and how to diagnose it? please help me out. Tell me the functions of both engine check lights
1. normal engine check light (can’t diagnose with my device)
2. engine check light with arrow facing downwards.

Answer: Arrows pointing down is low coolant. If you can’t read the code because it displays, “communication error”, you have a blown fuse. Your ALDL may be tied in with the auxiliary plug. Look for a blown fuse and replace it.