OBD2 telling me 1 3 & 7 glow plug bad Replaced all glow plugs, wiring to glow plugs, and glow plug relay. OBD2 still sends faulty message. Can't pass smog with error message. Truck runs great, starts great ect. discconected chip also. Any suggestions at what ie causing the faulty messsage? Thanks Gary

 

You replaced the Glow Plug Controler? Or a Relay??? Be clear here...

Does your truck have a Glow Plug Controler or a relay?

 

Did not replace ralay. I think it was called the module. It does have a relay, but did not think it sent messages to computer

 

So you do have a Glow Plug Controler, not a relay... You have a relay as well, but it controls the air intake heater...

If you have checked all the wires, and all check out find then I would replace those glow plugs again and or replace the GPC... One of the two have issues.

 

When this all started 6 years ago, I got a reading of #1 glow plug faulty. I went in replaced it, looked at it and it was fine. I put it back together and then it told me #1,3 & 7 were bad. I knew it was false read. Let it go drove it for 90,000 miles all good. California says have to smog, so I disconnected TS performance chip, changed GPC $220 New glow plugs, and glow plug harness, valve cover gasket. Truck starts and runs great still bad reading p0677,p0673,p0671. Why not the # 5? What about the wire harness from Valve cover to wherever it goes? Thanks Gary

 

You can not look at a glow plug and tell its fine. You have to test its resistance...

I doubt its the top of motor harness, you would have some run issues if it were. I would try and swap out the GPC again, go from there...