If you’ve ever opened the hood on an Aston Martin DB9, DBS or Rapide V12, you’ve probably seen it: two silver FoMoCo engine computers, usually sitting side-by-side. One runs the left bank of cylinders, the other runs the right bank.
Most owners know they’re there. Very few know what they actually do – or what happens when one of them isn’t quite right.
In this article we’ll unpack:
Why Aston Martin uses a dual-ECU architecture
How these modules talk to each other and to the rest of the car
The most common ways things go wrong
What UpFix does to test, repair, clone and pair them correctly
The V12 in cars like the DB9, DBS and Rapide is essentially two inline-six engines joined at the crank. Running that many cylinders, injectors, coils and throttle controls through a single controller would be possible, but not ideal.
Using two ECUs gives Aston Martin several advantages:
Load sharing and processing power
Each PCM handles the ignition, fuel and diagnostics for its own bank. That reduces the processor and driver load on each module.
Redundancy
If one ECU has a minor issue, the other can sometimes keep the engine running in a limited mode, long enough to move the car safely.
Scalability
Aston can reuse more conventional Ford ECU designs and split the work between them instead of designing a single, large, bespoke controller.
From a hardware standpoint, the modules look very similar to certain Ford PCMs, with part numbers like AG43-12A650-xx and familiar FoMoCo castings. But the way they’re configured and paired is specific to Aston’s platform.
On a typical DB9/DBS/Rapide V12 you’ll see:
A Left (or Primary) PCM
A Right (or Secondary) PCM
Each ECU:
Controls its side’s fuel injectors, ignition coils and sometimes throttle body
Monitors sensors on that bank (O2, knock, etc.)
Talks to the rest of the car via CAN bus
Behind the scenes, they also share certain responsibilities:
Both report data to the instrument cluster and body modules
Both participate in diagnostics, so scan tools can query faults from either side
Both must agree with the immobilizer / key system, or the car will disable starting or fuel delivery
That last point is where many problems start.
Aston Martins based on Ford electronics rely on PATS-style immobilizer logic. In simple terms:
The car stores key code and security data in an immobilizer module and in the PCMs.
When you start the vehicle, the system checks that:
The key is valid.
The immobilizer and PCMs all agree.
If something doesn’t match, the system can:
Block the start command entirely
Allow cranking but disable fuel or spark
Trigger warnings or security-related fault codes
On a dual-ECU car, both modules must be on the same page. VIN, calibration and immobilizer data need to be consistent, or you get weird, hard-to-diagnose symptoms.
Here are the scenarios we see most often at UpFix:
Heat, vibration, moisture intrusion or voltage spikes can damage:
Injector and coil drivers
Power supply circuits
Internal processors
Symptoms:
Misfires or a dead bank
One exhaust stays cold
Fault codes related to that bank’s components
Communication issues with one PCM
In these cases, we can often repair the original ECU, test drivers on the bench, and return a plug-and-play unit that still retains the vehicle’s original data.
This is the most common issue we see, and it’s exactly what happened in Sam’s Aston Martin DBS case.
A previous shop:
Buys a used ECU with a matching or close part number
Programs the VIN and maybe the calibration
Installs it and hopes for the best
Problems:
The immobilizer block doesn’t match
The calibration may not be correct for that exact configuration
The car may:
Start but run rough
Drop into limp mode (e.g., P2106)
Disable fuel on one bank
Refuse to start after some time or when modules are swapped
The customer sees an Aston that “sometimes runs, sometimes doesn’t.” Underneath, the ECUs are essentially arguing about security data.
Some tools claim to “clone” ECUs by copying full memory from one module to another. That can work, but there are a few traps:
Different hardware versions may not respond well to a straight clone.
If the process is interrupted, you can corrupt both units.
Some security areas require boot-mode programming, not just OBD flashing.
We see ECUs arrive that:
Match VIN and partial configuration
Fail in deeper self-tests
Have corrupted or mismatched immobilizer data
When an Aston comes in with limp mode, a dead bank, or key/immobilizer errors, here’s a more reliable approach:
Scan both ECUs separately
Pull fault codes and live data from each side. Pay attention to fuel status, injector pulse commands and misfire counters.
Check basic power and grounds
Confirm that each ECU has the correct supply voltage and clean grounds. A wiring issue can mimic a failed ECU.
Look at exhaust temps and fuel trims
A cold exhaust on one bank with “no fuel” status in live data strongly suggests that bank’s ECU is not enabling fuel.
Ask about ECU history
Has any ECU been replaced?
Is there tape or hand-written part numbers on the module?
Has anyone already “programmed” or “cloned” it?
When in doubt, send both ECUs together
Testing one in isolation is like reading half a book. We need both to compare VINs, calibrations and immobilizer blocks.
When you send dual Aston ECUs to UpFix, our process usually looks like this:
External inspection
We check for water damage, mounting stress cracks, and tampering.
Bench communication test
Both ECUs are powered up on the bench to confirm they boot and communicate.
Read VIN and calibration
We verify that basic identification data is correct and consistent.
Deep memory read in boot mode
For platforms that require it, we open the units and read internal flash and EEPROM areas, including immobilizer blocks.
Compare and analyze
We determine:
Which ECU appears original
Which one has mismatched or corrupted data
Whether hardware damage is present on either unit
Repair and/or clone
Depending on findings, we may:
Repair damaged hardware
Clone immobilizer/vehicle data from the good unit to the replacement
Virginize and re-pair ECUs when appropriate
Final validation
We re-check communication, ID data and security sections on both ECUs to confirm they match and are ready to reinstall.
This approach lets us keep as much of the original coding as possible, while saving customers up to 80% compared to sourcing new Aston ECUs.
If you’re a shop or tuner, these habits will save you a lot of headaches:
Label ECUs clearly (LEFT/RIGHT) before removal
Avoid cross-installing them later and adding confusion.
Don’t mix and match unknown used modules
If you must use a used ECU, plan from the start to have it professionally cloned and paired.
Document everything
Take photos, record part numbers and note any previous programming attempts. This info helps our team move faster.
Involve an ECU specialist early
Once you’ve ruled out mechanical issues, call us. The sooner we get eyes on the data, the higher the chances of a clean fix without multiple parts purchases.
UpFix specializes in repairing and rebuilding automotive electronics – including the dual ECUs used in Aston Martin DB9, DBS, Rapide and other models.
We can:
Test and repair original ECUs
Clone and pair immobilizer data between modules
Help you avoid repeat failures and unnecessary replacements
Keep expensive electronics out of the scrap pile
📞 Call 888-979-9343 or visit UpFix.com to start your repair request.
Send both ECUs, include the VIN, and tell us what the car is doing – we’ll take it from there.