If you want to check/clean your engine bay ground points here's some visual guidance and notes:
G100. The main battery negative (-) path to the chassis. This ground point gets corroded. The bolt is 8 mm and uses a 13 mm wrench. Remove it and flush all the rust off the fender and the wire ring terminal. Renew the bolt if required.
G101. The main battery (-) path to the engine. The engine is the ground path to circuits related to the engine and transmission for the most part, but other important circuits are grounded here (see pic). Remove and clean these ring terminals and reattach. THe nuts are 5/16' and use a 1/2" wrench.
G106. G106 has two sheet metal screws holding the ring terminals down on the left inner fender, located under the wiring looms near the PCM. Circuits grounded here are shown on the pic. Remove these screws and clean the ring terminals, remove the rust on the fender and replace the screws as required.
G102. G102 is the ground point for the Data Link Connector. It is located at the oil dipstick tube attach bracket. If you ever have trouble with a code reader or scanner not connecting, this ground may be the cause. Clean the ring terminals.
Firewall/Engine Ground. This ground was originally intended to prevent radio interferance from the ignition system. It's a bonding strap, not a cable/wire like the rest of the grounds. It goes from the firewall to left rear cylinder head bolt. It does provide an alternate ground path to the chassis however. If G100 is compromised by corrosion this ground would help provide a chassis ground, through the engine (G101). The bolt is 10 mm and uses a 15 mm wrench. Remove the bolt and remove the rust from the firewall, clean the ring terminal, and replace the bolt if required. Remove the nut that secures the other ring terminal to the cylinder head stud. Clean the ring terminal and replace the nut if required.
Clean the ring terminals with Scotch Brite pads. Flush using CRC Electroincs Cleaner. Do not use Dielectric grease on these ground points (as some would suggest).
Good luck.