Symptom for camshaft cover problems is reading less than 19"/Hg by connecting a vacuum gauge to the dipstick, leak someplace in the PCV control system.
This is what the shop manual states about receiving a U0100 code all by itself.
"
Diagnostic Aids
- Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:
- A control module on the data communication circuit was disconnected while the communication circuit is awake.
- Power to one or more control modules was interrupted during diagnosis.
- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
- A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a control module based only on a history U-code.
- Do not replace a control module reporting a U-code. The U-code identifies which control module needs to be diagnosed for a communication issue.
- Communication may be available between the BCM and the scan tool with either the low or high speed GMLAN serial data system inoperative. This condition is due to the BCM using both the low and high speed GMLAN systems.
- Use Data Link References See: Powertrain Management\Computers and Control Systems\Information Bus\Testing and Inspection\Initial Inspection and Diagnostic Overview to determine if the control module uses high or low speed GMLAN serial data communications.
- Some control modules may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the control module.
- Some intermittent communication concerns may be caused by fretting corrosion on the serial data circuit terminals. Inspect all connectors at the control module that set the communication DTC, the control module that the communication DTC was set against, and any inline harness connectors between the two control modules. Do not replace a control module based only on fretting corrosion. Refer to bulletin 09-06-03-004 for assistance with the diagnosis and repair of this condition.
- This diagnostic can be used for any control module that is not communicating, regardless of the type of serial data circuit it is connected to, providing the vehicle is equipped with the control module."
Switched on the blower at high speed, 20 amp load, engine off, measured 2.1 voltage drop across the terminal of the battery and at the ground point. Problem was within the negative battery terminal itself, corroded bare copper wire crimped inside of that terminal. But could at other places as well, other problem I found was the ignition relay contacts were dirty.
I soldered that negative terminal battery terminal after cleaning it, cleaned the contacts on the ignition relay, but later replaced it with a Panasonic, all kinds of code problems went away.
Telling you 700 bucks to replace that Electronic Brake Control module contradicts the shop manual. Positive battery terminal was okay, but same bare copper wire crimped, also soldered that just in case.