My dad said his obd2 scan tool wouldnt read any codes from my 99 c5 after plugging it in. It does have a ses light on and when he plugs it in powers on the scanner but doesnt read any codes. It does have headers and i deleted the rear o2 sensors. Is there any fuses or wires that could be disconnected or way the car could have been rigged up to where you cant read codes through the diagnostics. Its possible when i get a chance ill take it up to autozone to see if there scan tool picks up anything. I read somewhere c5 secrets that you could get it to cycle through codes through the digital cluster by holding the option button down and hitting the fuel pump door button 4 times and it should show the codes cycle thru each one after 3 seconds. Is this true? I just bought the car 2 months ago from laredo texas with salvage title for 6800$ 90k miles. It had some problems an exhaust leak on both sides a stud off each manifold collector broken. The radiator support was trash car would get kind of hot one fan blade was not on there an nut missing and missing the whole lower air dam. Anyway got the car home from laredo 2 hour drive back to San Antonio. I put tsp headers cost 660$ with tax and o2 extensions a new lower radiator support for 240$ and the front lower air dam was 130$ plus the labor it took me.

 

Yes, you can read those DTC’s by accessing them through the DIC…you can find the procedure on YouTube…if your scan tool shows “No Communication” with the car I would suspect you have some type of communication issue…you will see a bunch of “U” codes stored !!…any other symptoms ??

 

When OBD2 came along, all state emissions inspections were monitored via the DLC (Data Link Connector, or “OBD2 connector”). Very common for the pins to become loose. Easy to get “no comm” on older OBD2 cars. when the modules are actually communicating. If you want to check this, you will need a good multimeter. There are only 6 of the pins used IIRC. I usually replace defective contacts in a bad DLC, but it takes a special crimping tool.

Now cheap scanners will only read generic Codes, those generally associated with emissions. They can be erratic in performance as well. Autozone usually can only read generic codes, so you have more code reading power internal to the C5.

Follow C5Diag’s recommendations. If you get a lot of U codes from the car’s DIC, then it is not the DLC and you have a real comm problem.
Also, reading your description, you need to carefully read how to pull up codes with the DIC and the buttons on the dash. The fuel door switch is NOT used. Also, salvage titles can be tricky, if it is a flood car, you will be chasing corroded connectors. If a wreck, then you can focus on the damage area for bad wires, modules and connectors. There is a lot of stuff under the battery, including the PCM. battery acid is a common source of damage from impact in the RF of the car. Another thing to go for are the two shorting bars in the BCM harness ares. These are big comm error sources. Research here for info on them, how to check, etc. Assuming your acronym “SES” means the check engine light, GM calls this the Malfunction Indicator Lamp or MIL. Is it flashing? if so that means you have a misfire condition. Not flashing can mean a BUNCH of possibilities.

 

hey thanks guys its working fine. My cluster reads bank1 2nd sensor and bank 2 second sensor for the tsp headers rear o2 delete. Autozone scanned fine the same codes for the rear o2 sensors. My dad must be kind of dumb with his scanner or was the one that tried to tell me its not reading codes with his 15$ amazon scanner.