2010 Jeep Grand Cherokee P0670 Code: 'Reserved/SAE' After Glow Plug Module Replacement

This is not a common powertrain issue — could you confirm which engine you have? 3.0L or 2.7L diesel? I may have some troubleshooting resources that could help.

charlie43 wrote: I recently encountered the OBD2 diagnostic code P0670 — 'Glow Plug Control Module Open Circuit' — on my 2010 Jeep Grand Cherokee WH (same model as WK in the U.S.). I replaced both the glow plugs and the glow plug control module, but the P0670 code persists. Now, after clearing the code, it displays only 'Reserved/SAE' with no additional text. The vehicle starts fine, but I'm concerned about whether the underlying issue is fully resolved, especially since we're in Australia where temperatures are consistently high and engine warm-up conditions can be challenging. What does 'Reserved/SAE' mean in this context? Is it a software limitation or an indication of a deeper fault in the control module or wiring? Any insights from owners with similar experiences would be greatly appreciated. I own a 2008 Jeep Grand Cherokee with the 3.0L diesel engine and have also experienced P0670. Following instructions from a YouTube video (https://www.youtube.com/watch?v=gdT2ChsbKAo), I discovered three of my glow plugs were faulty. I replaced them with new NGK Y8002AS glow plugs. Cold starts are now significantly better, but the P0670 code remains. After testing all six glow plugs with a multimeter, they all show 0.4 ohms resistance — within specifications as per the video instructions. I then disconnected each glow plug connector and used a multimeter to measure voltage supply when my partner toggled the ignition on and off. I found that one lead received full 12V when energized, but another only delivered 1.8V — clearly indicating a faulty control module. I am currently investigating further and will update once the issue is resolved.