Hey everyone,
I’m at a bit of a loss here and could really use some help diagnosing my swap. I’ve got a 2003 350Z that’s turbocharged and recently had a RevUp motor from a 2006 swapped in (VQ35DE RevUp). The previous owner started the swap but never finished it — basically just dropped the motor in and called it a day. I’ve taken it further and tried to get everything working correctly, but I’ve hit a wall.

Current Setup:

• Chassis: 2003 350Z 6MT (originally non-RevUp VQ35DE)
  
• Engine: 2006 RevUp VQ35DE (with its correct sensors, etc.)
  
• ECU: 2006 RevUp ECU — verified correct part number
  
• Mods: Turbo setup, base tune flashed (NATS deleted on the ECU)
  
• Wiring: Swapped over the correct RevUp engine harness and ECU harness to match the new engine
  
• Grounds: All checked and cleaned
  

Problem:

• I'm getting U1001 – CAN Communication Circuit code
  
• Security light on dash stays illuminated
  
• Car used to start and run (rough) before I swapped in the correct harness and ECU
  
• Now it does not start, cranks but no fire

Update:

I tried swapping in a spare 2005 non-RevUp ECU I had lying around just to test things. Surprisingly, the car started right up (obviously ran rough due to missing sensor input for the RevUp setup), but I still had the U1001 code present.

The interesting part — it only started when my foot was all the way down on the gas pedal. No throttle = no start. But it did fire up, which makes me think something in the RevUp ECU wiring or config might be blocking the start signal altogether.

Any insight on what this means would be super helpful.

What I've Done:

• Flashed base tune with NATS disabled
  
• Verified ECU part number is for RevUp
  
• Checked and rechecked all engine and chassis grounds
  
• Verified ECU connectors seated properly
  
• Swapped to RevUp-specific wiring harnesses
  

What I Need Help With:

1. What specifically could be causing the U1001 CAN code after this swap?
   
2. Does the security light staying on indicate the NATS delete didn’t fully take?
   
3. Could this be an issue between the ’03 body CAN system and the ’06 ECU’s CAN language?
   
4. Anyone have pinout comparisons between 2003 and 2006 ECUs or tips on CAN compatibility between years?
   

I’m really not sure what to check next. Any ideas, suggestions, or experience with CAN issues and year-mismatch swaps like this would be massively appreciated. I’ll gladly provide logs, pics, or anything else that might help.

Thanks in advance 🙏
– StockVQ

 

CAN communication codes are usually caused by a break or short in the network. There's typically two wires/circuits, a CAN High and CAN Low.

When you swapped in the RevUp harness, did you check it over for continuity and shorts? (was it new or used?)
The new ECU might need to be paired with the BCM (programming), it sounds like you're able to talk with some of the computer modules as you are getting the U1001 code. So the question is, which module is not able to communicate?
You will need to pick up a copy of the FSMs for both an 06 (Revup) and an 03 (Non-Revup) to compare body/harness wiring. You can download Factory Service Manuals for free from Niccoclub. But I'm sure you can find them elsewhere on the net.

Other things that could be impacted by the swap.
The IPDM/Fuse boxes in the engine bay. (Some components are BCM controlled, others are part of the ECM, but the IPDM does have intelligence, aka CAN communication).

Good Luck!
-Icer

 

Update:

I tried swapping in a spare 2005 non-RevUp ECU I had lying around just to test things. Surprisingly, the car started right up (obviously ran rough due to missing sensor input for the RevUp setup), but I still had the U1001 code present.

The interesting part — it only started when my foot was all the way down on the gas pedal. No throttle = no start. But it did fire up, which makes me think something in the RevUp ECU wiring or config might be blocking the start signal altogether.

I will be looking into the FSMs asap to see how they compare. i will also check to see if the ipdm/fuse boxes are compatible aswell