Jf029

Apologies if I have posted this in the wrong place this is my first time using this website.

2010 G37x coupe
150,000mi

I bought this car as a no crank no start about a month ago and long story short ive figured out the reason behind that is due to the CAN-bus network being overloaded with voltage (CAN H around 7.5 volts and CAN L being about .5 volts above that). Now when I disconnected Harness connector M116 from F103 the CAN network returned to normal voltage levels, the modules could communicate with each other again, and the car could start and run (albeit you would have to stomp on the gas to stop it from stalling out but if you reconnect M116 to F103 before that happens it will idle on its own but roughly... however this would also reintroduce the aforementioned voltage issue). I was also able to pull the following codes...

• U0101
• P0223
• P2135
• P2A00
• P0102
• P010C - intermittent: sometimes appears when engine has been started
• P0447 - intermittent: sometimes appears when engine has been started
• P0011 - intermittent: sometimes appears when engine has been started

Now when I leave M116 and F103 connected the CAN systems voltage will shoot back up and bring the whole system back down again... BUT if I pull both the fuses for the TCM the Voltages will again return to normal levels and everything plays nice again. Im thinking that mabey the TCM has failed internally and is causing these problems but when I pull the fuses for it (effectively removing it from the network/harness) The codes I pulled are still there (even after clearing them). Which makes me think that mabey its a grounding issue on that harness thats causing all those codes since...

1. All those codes are for modules that are on the same harness as the TCM
2. I have a hard time buying that all those modules legitimately went bad at the same time

Let me also add that yes the sunroof drain was an issue on this car but I already took care of that **** show and its associated modules. Any thoughts or tips on how I can solve / properly diagnose this issue would be greatly appreciated.

BULL

Good job on the diag on your end.

M116/F103 has
Evap vent valve
MAF 1&2 12v
AC solenoid
PS solenoid
AWD circuits
Park/Neutral
TCM CAN
TCM 12v

Looking at the original problem you had a no crank no start. Initially this could be attributed the to the IPDM and BCM not receiving the Park/Neutral signal from the TCM that passes through M116/F103. AWD module wont prevent cranking or starting but can mess up CAN voltage.
By disconnecting M116/F103 you also remove power from your MAFs which is needed here.

The next step is to probe the Dash side connector (M116 i believe) to check for the proper voltages going to the TCM, AWD module, MAF's and evap. If this works I would suggest you pull the shells off that connector and remove the power pins from the TCM side and see what you get on you CAN voltage. The car is stalling because MAFs are not receiving power.
You could do exactly the same by disconnecting T51 which is the transmission TCM connector. If this get's rid of issues and CAN voltage returns to normal then you have higher % of it being the TCM that has fried.

Jf029

Ok so I have taken the voltages from the M116 connector in my car but I cant find anything on what the voltages are supposed to be in my manual. If you could provide a picture from a manual that does have them so I can compare it to the voltages i took down id appreciate that. Also I pulled the fuses for the TCM instead of disconnecting it to see if it would get rid of the voltages issues that are causing the codes but there still there. I took some measurements with my multimeter on the wires that lead to the parts that the codes are for (MAF, throttle actuator, etc etc) and the wires are definitely delivering the wrong voltages to these components or in some cases no voltage at all.. the harness looks a little rough so no surprise there. Im honestly considering just getting a new Engine Control Harness from a donor vehicle and installing it my self. If I do decide to do that would the donor car just need to be an X model or do year and body type need to match as well?

BULL

Everything on the first section of the connector are 12v with black one being ground. The middle are AC/PS, the last ones are TCM. The TCM receives 12v from this connector and the black connector in the engine bay so pulling the fuse might not have done the job correctly.
On another note, you'll need an X harness close to that year group. so 2010-2011 only then 2012 to 2014 only

Jf029

Alright I'll disconnect the TCM connector and check that way just so im sure the results are good. Was being lazy and thought I could just pull the fuses instead lol. Also I forgot to post the voltages in my previous reply but since this was without the TCM being disconnected theres a possibility they are inaccurate so its probably best to take em with a grain of salt. Regardless I'll leave em here to compare with the voltages I get after I disconnect the TCM.

(Top to bottom of M116)
• 11.65 _____•13.50
• 0.08 ______•13.60
• 13.17
• 0.00

•0.00_______•0.00
•13.20______•0.22

•12.30
•0.00
•0.00
•2.22 ________•1.90
•1.90 ________•2.20
•13.50 _______•13.60
•13.50 _______•0.22

do these look right?