So, about to complete a cam swap on my 2014 Z51

Symptoms: can't write new tune to ECU

The car sat with battery unplugged for a few months. Could the ECU lose its programming?

What is plugged:
- alt
- 2 ground plugs behind heads
- 2 hot wire to the engine fuse box
- 5 blocks under the engine fuse box. I checked that all pins are straight
- starter (1 big wire + plug)

I have +12V coming to those ECU fuses:
- fuse 4
- fuse 8 ("LOGISTICS 30A") is not present but I have pins coming to it, not sure if prev owner messed with that
- relay 61 tested: OK

What's not plugged:
- plugs
- many things from front engine
- anything above HPFP/valley
- suspensions
- maybe I forgot a ground or hot wire somewhere?

Yet, with fuse box connected I should be able to talk to ECU with my scanners right?
But I can't, either with GDS2 or HPTuners

Ignition is ON, dashboard is ON, all interior lights working, windows etc
Battery a bit low at 12.03V
Charged a few hours to 12.90V, same issue

0x541: B1395 - Control Module Voltage Reference Output 1 Circuit (Pending, Current, Old, History)
0x541: B3205 - Driver Window Motor (Pending, Current, Old)
0x541: B3210 - Passenger Window Motor (Pending, Current, Old)
0x541: B3600 - Passenger Compartment Dimming Request Signal Circuit (Pending, Current, Old, History)
0x541: U0100 - Lost Communication With ECM/PCM A (Pending, Current, Old, History)
0x541: U0131 - Lost Communication With Power Steering Control Module (Pending, Current, Old, History)
0x543: U0422 - Invalid Data Received From Body Control Module (SES, Pending, Current, Old, History)
0x54E: C0575 (Pending, Current, History)
0x54E: C0580 (Pending, Current, History)
0x54E: C0615 - Left Front Position Sensor Malfunction (Pending, Current, History)
0x54E: C0620 - Right Front Position Sensor Malfunction (Pending, Current, History)
0x54E: U0100 - Lost Communication With ECM/PCM A (Pending, Current, History)
0x54E: U0121 - Lost Communication With Anti-Lock Brake System (ABS) Control Module (Pending, Current, History)
0x552: B1277 - Microphone 1 Input Signal Circuit (Current, History)
0x552: U0100 - Lost Communication With ECM/PCM A (Current, History)
0x554: U0100 - Lost Communication With ECM/PCM A (SES, Current, Old, History)
0x7EA: U0100 - Lost Communication With ECM/PCM A (Permanent)

 

You need to check ECM powers, grounds, and the data lines before condemning the ECM !!

 

Ofc it's probably not damaged, it's probably something I forgot but I can't figure what

Grounds I tested and OK:
- driver head
- pass head
- driver engine bay (2)
- passenger engine bay (1)
- the small black wire at the battery negative

Is there other power source going to the ECM apart from the ones I listed?

 

Well HOW exactly did you check the grounds and were they the ECM grounds ??…below is power and ground for the ECM…do you know which wires to check ??…modules have at least a battery and ignition feed…do you know to check grounds and its NOT visually ??

 

0 ohm between all ground points and negative pole
thanks for diagrams I'll check that tomorrow

 

Resistance checking of grounds is NOT how it’s done..I can’t stress this enough !!…you need to watch the video.

 

I didn't screw the 2 bolts from hell sitting on the back of the block between the firewall. They hold the harness and plastic protection. I don't think those are ground tho

 

I watched it, the bulb method makes sense to test power pins. But for ground you can't have voltage drop if there's no resistance between the - battery and the point you're testing. It would rather show an issue on the power side of the circuit. How is this logic flawed?

 

Current flows on the ground side which goes back to the battery…many shade tree mechanics don’t know what the ground does…if a module draws 5 amps that 5 amps must return to the battery via the ground wire…a ground isn’t a static thing…if all 5 amps gets back to battery negative you will have ZERO voltage drop…that is what you want !!…most voltage drop issues I see are on the ground side…that’s why 99% of mechanics can’t diagnose a simple light bulb circuit.

 

Yup makes sense, ty

 

 

Make sure you test for 60 ohms between the CAN bus pins at the diagnostic connector.

 

Do you mean at OBD2 port?

so 60 ohms between CAN hi (pin 16) and CAN low (pin 14) ?

 

No !!…6 and 14 with battery DISCONNECTED.

 

I get 116 ohms

 

With 116 ohms tells me you have a break in the wiring…since you had no comms with the ECM, Power Steering Control Module and the EBCM you would need to find Connector X102 (under the EBCM in diagram) and jumper terminals 1 to 11…now check 6 and 14 with ohm meter…if you see 120 ohms the break is downstream of X102 going towards the ECM…there are 2 each 120 ohm terminating resistors in parallel one at the ECM and the other at the other end of the bus in the Parking Brake Control module which continues F and G in the next diagram…do you have a Suspension Control Module RPO codes FE2/FE4 ??…very few if and “mechanics” dealer and independent shops have no clue how to diagnose these information bus issues…if this testing is over your head seek out an auto electric shop.

 

X102

 

laserdude & C5Diag Bingooo!!

You mentionned power steering module so I double checked it and one of the 3 connectors on it wasn't plugged correctly!!
Now I have ECU communication again

New tune is being written to the ECU atm

 

If module isn’t plugged in you won’t have communication downstream to the ECM !!

 

I wouldn't think a steering column would impede an ECU! Learn everyday