7cz flash codes 58 and 21

disconnect your ELD and see what happens.

 

Not sure if this will help you or not…

https://www.thetruckersreport.com/truckingindustryforum/attachments/1mm-2ks-2ws-6nz-7cz-pdf.262561/

 

"Hi. Thanks for asking your question! I will try and help you out.
Code 21 is defined as a 5 volt supply voltage fault. This indicates the 5 volt supply to all the 5 volts sensors is either shorted or open. Because the Boost pressure, Atmospheric pressure, Fuel temp, Coolant temp, Oil pressure and Intake air temp sensors all use the same 5 volt supply, the engine will run very poorly when this code is active.
The most common thing that causes the code 21 is one of these sensors is shorted. When this happens, it takes out all the sensors. To troubleshoot, you need to unplug each of these sensors one at a time. If the code 21 remains after 3 seconds, the sensor you unplugged is not the problem. After 30 seconds unplug another sensor, and so on and so on. If the code 21 goes away after unplugging one of these sensors, that sensor is your problem.
If you unplug all the sensors and the code 21 still remains, the either the engine harness or the ECM is the problem.
Please reply back if you need more help or have more questions. I am happy to assist."

Qouted from another site, but seems like an easy way to begin troubleshooting

 

That will do it, the bus has 5 volts on it, and if there is a short, then it can't communicate.

 

This on a pre-emissions engine ! Maybe I should count my blessings on my Commiefornia emissions compliant truck/engine. . Hope you get it figured out.