Aston Martin DBS ECU Repair: Immobilizer Case Study

When an Aston Martin DBS VIN Matches but the Keys Don’t: Dual-ECU Repair Case Study

Some repair stories are simple. This one… wasn’t.

Sam, a content creator who works on high-end cars, reached out to us about a 2011 Aston Martin DBS that had turned into a nightmare. The car had already eaten a lot of shop time and parts, and now it was headed for a feature video. If the problem really was in the engine computers, UpFix would end up being the hero (or the villain) on camera.

No pressure.

The patient: a V12 Aston with two engine computers

Underneath the Aston Martin DBS badge is a 6.0L V12 managed by two FoMoCo (Ford) powertrain control modules (PCMs) – one for each bank of cylinders. You’ll see them sold as left/right or primary/secondary ECUs, often with part numbers in the AG43-12A650-xx range.

That dual-ECU setup is great for performance and redundancy, but it also means one wrong module – or one bad piece of programming – can take an entire bank of the engine offline.

Which is exactly what Sam was dealing with.

Symptoms: limp mode, a cold exhaust, and a stubborn V12

By the time Sam emailed us, he’d already attacked the problem mechanically:

• New ignition coils

• Swapped throttle bodies

• PCV system checked and serviced

The Aston still insisted on:

• Limp mode with extremely slow pedal response

• Misfiring and poor drivability

• A P2106 “Throttle Actuator Control System – Forced Limited Power” code stored

On its own, P2106 just tells you the ECU is choosing to limit power because it sees something serious in the system. It doesn’t tell you what the real root cause is.

Live data painted a more alarming picture:

• Left exhaust: gets hot, runs normally

• Right exhaust: stays cold

• Under Fuel System Status, the right bank showed “0 – No Fuel” while the left bank cycled normally

Fuel was effectively dead on the right bank.

Why Sam suspected the right-side ECU

Sam started focusing on the right-side ECU for a few reasons:

• Its case had blue tape over it with a hand-written part number — usually a sign someone has been there before.

• The car had symptoms limited to one bank.

• Swapping coils and throttles hadn’t moved the problem.

To test his theory, Sam swapped the ECUs side-to-side.

Result: the car immediately threw a “key mismatch” / immobilizer error on the dash and wouldn’t start.

Now he was pretty sure:

• The car had likely received a used ECU in the past.

• Something about the immobilizer / key data wasn’t right.

• This was now deeper than a typical scan-tool diagnosis.

He boxed up both ECUs, labeled LEFT and RIGHT, and shipped them to UpFix.

Why Aston Martin ECUs are not “plug and play”

Most modern Fords – and by extension, Ford-based Aston platforms – use PATS (Passive Anti-Theft System). The immobilizer and the PCM share key data. When you start the car, the system checks the transponder key. If the codes match, fuel and injectors are enabled. If they don’t, the system disables fuel and/or spark and may log security-related faults.

On a twin-ECU Aston Martin:

• Both PCMs must agree with each other

• They also have to agree with the rest of the car on immobilizer data

• The VIN and calibration can match perfectly, but if the immobilizer section doesn’t, you’ll still get no-start or fuel cut issues

That’s why simply installing a used ECU with a matching part number is risky. It might start for a while; it might also randomly drop a bank, go into limp mode, or suddenly refuse to crank.

Bench testing: everything looks right… until it doesn’t

Once Sam’s ECUs arrived, our electronics team put them on the bench.

Initial checks showed:

• Both ECUs communicated normally

• Both carried the same VIN

• Both had the same calibration / software level

On paper, they looked like a matched pair.

But given Sam’s symptoms – one bank dead on fuel and a “key mismatch” when swapping ECUs – we knew something in the security data had to be off.

These PCMs require boot-level access to get at the deepest parts of memory. We opened both modules, pulled full memory reads and compared the immobilizer sections.

That’s where the problem appeared:

• The left-bank PCM looked like the original, correctly paired to the vehicle

• The right-bank PCM had the same VIN and calibration – but a different immobilizer block

In plain English: someone had likely installed a used right-side ECU and flashed it just enough to make the VIN and software match, but they never fully cloned the immobilizer data.

The car’s security system tolerated that up to a point. Under certain conditions – especially with P2106 forcing limited power – the mismatch caused fuel to be cut on that bank. And when Sam swapped ECUs, the mismatch became obvious enough that the car refused to start and flagged a clear key/immobilizer error.

The fix: clone the right data, not just the VIN

The solution required the right tools and a careful approach.

Here’s what we did:

1. Confirmed the “good” module
   Based on Sam’s description and our tests, we treated the left-bank ECU as the known-good original.

2. Extracted full immobilizer data
   Using boot-mode programming, we read the security/immobilizer section from the left ECU.

3. Cloned the immobilizer block
   We wrote that immobilizer data into the right-bank ECU, preserving the matching VIN and calibration.

4. Verified the pair
   Final checks showed both ECUs now had:

   • Identical VIN

   • Matching calibration

   • Matching immobilizer / key code data

From the car’s point of view, the two PCMs are now a properly paired factory set again.

We didn’t need Sam’s keys, cluster or other modules for this particular platform. Once reinstalled, the Aston should see both ECUs as trusted and re-enable fuel and throttle control on both banks.

So what actually went wrong on this DBS?

Zoomed out, here’s the most likely story:

1. At some point, the right-bank ECU failed.

2. A previous shop sourced a used ECU with a similar part number.

3. They programmed the VIN and base software so it looked correct.

4. They didn’t fully clone the immobilizer section or cloned it incorrectly.

5. The car ran, but under certain conditions the mismatch caused:

   • Fuel cut to the right bank

   • Limp mode and P2106

   • A “key mismatch” error when the ECUs were swapped

From the outside, it looked like a strange intermittent throttle issue. Under the hood, it was really a data mismatch inside one of the engine computers.

Takeaways for Aston Martin owners and performance shops

If you work on DB9, DBS, Rapide or similar Aston Martin models, this case highlights a few important lessons:

1. Treat the ECUs as a matched pair

On dual-ECU cars, it’s nearly impossible to fully diagnose an ECU problem in isolation. If you suspect a PCM fault on a V12 Aston, it’s best to send both ECUs for testing so we can compare VIN, calibration and immobilizer data across the pair.

2. Be careful with used ECUs

A used ECU with the “right” part number may still carry:

• Different software level

• Different immobilizer and key data

• Hidden hardware problems

That’s how you end up with vehicles that start sometimes, run on one bank, or fall into limp mode after a few miles.

3. VIN match is not enough

Seeing the correct VIN in a scan tool is only step one. Security and immobilizer blocks have to be handled correctly – especially on platforms that integrate Ford-style PATS logic – or the ECU can still disable fuel or block starting.

4. Repair and clone instead of guessing and swapping

Sending your original ECUs to UpFix lets you:

• Keep the factory coding and configuration

• Clone data correctly into a replacement when hardware is bad

• Avoid the cost of multiple used modules, repeated dealer visits and tow bills

• Save up to 80% vs. buying new ECUs, while keeping electronics out of landfills

Need help with an Aston Martin ECU?

Whether you’re fighting a DBS with limp-mode P2106, a DB9 with a dead bank, or confusing immobilizer/key errors after an ECU swap, we can help:

• Bench-test and document what each ECU is doing

• Clone and pair immobilizer data between modules

• Repair or replace hardware where needed

• Provide clear notes you can share with your customer or audience

📞 Call UpFix at 888-979-9343 or visit UpFix.com to start a repair request.
Include the vehicle details, part numbers, and a short description of the symptoms – and when possible, send both ECUs so we can treat them as a matched s