Simos 3PE Immo Off on VW Polo 9N, Skoda Fabia and Seat Ibiza 1.2 (03E906033)

Polo 9N 1.2 12v, 2003. The customer bought a used ECU because the original was diagnosed with an injector driver fault. New one fitted, now it cranks and dies after two seconds and the immobiliser lamp in the cluster blinks. Label: 03E906033 A, Siemens Simos 3PE. Immo 3 is doing its job. It just isn’t your car’s Immo 3 any more.

Immo 3 in one paragraph

On the 9N Polo, Fabia I, Ibiza 6L and Cordoba 6L with the 1.2 three-cylinder (AWY, BMD, AZQ, BME), the immobiliser control is in the instrument cluster. The cluster checks the key transponder and then exchanges a code with the engine ECU. The ECU carries a copy of that code plus the cluster’s identifier. A used ECU brings the wrong pair and the engine is cut two seconds after start. On a genuine Immo 3 car the fix is adaptation with VCDS (or ODIS/VCP) using the 7-digit SKC, which needs the login for both cluster and ECU. That’s fine when you have the SKC. Most workshops don’t, and the dealer route is slow and priced accordingly.

What immo off does here

An immo off file on the Simos 3PE tells the ECU to skip the exchange with the cluster. The engine runs regardless of what the cluster says. The cluster still owns its own logic, so the immobiliser lamp may flash for a while at start-up on some cars and then go out; on others it stays on. It’s cosmetic. Anything else in the cluster (mileage, service interval, key count) is untouched.

Use it for: a used ECU with no SKC; a cluster that’s been replaced and can’t be paired; an ECU rebuilt after a failed flash where the immo block was lost. Don’t use it when the customer simply lost the keys, because they’ll still need a transponder the cluster accepts to get the cluster into a happy state, and a locksmith with Tango or Zed-Full does that cheaper.

Reading and writing the 3PE

OBD first. KESS V2, Galletto and MPPS read the Simos 3PE flash through the socket on K-line on most software versions. On this ECU the immobiliser data is inside the flash, not in a separate EEPROM, so an OBD read is enough for us to prepare immo off. Bench with KTAG, FoxFlash or KT200 is the fallback if OBD refuses, and it’s what you want if the unit is a suspected brick.

Files in the catalogue

• VW POLO SIMOS 3PE 03E906033 5WP40163 03 IMMO OFF DUMP
• SKODA FABIA SIMOS 3PE 03E906033 A IMMO OFF DUMP (and the stock SKODA FABIA SIMOS 3PE 03E906033 A DUMP)
• SEAT CORDOBA SIMOS 3PE 03E906033 D IMMO OFF DUMP
• VAG SIMOS 3PE 03E906033 N IMMO OFF DUMP

The suffix letter (A, D, N and so on) tracks the engine code and gearbox. A Fabia 03E906033 A file into a Polo with a D unit will start but may set implausible fuel trims. Match the letter, and if you can, send your own read so we return your calibration with immo off rather than a generic one.

What went wrong on the bench

Three real cases from the last year, in case they save you an hour.

• Immo off written, still cuts out. The ECU was a Simos 3PG, not 3PE. The board looks the same; the label doesn’t. The 3PG file is different and the 3PE immo off patch does nothing on it. Read the label, then the tool ID string.
• OBD read fails at 20 percent. The cluster was pulling the K-line down because of a water-damaged connector behind it. Unplugging the cluster let the read finish. Then, of course, the car needs the cluster back for the immo; immo off made that irrelevant.
• Car starts, no rev counter, no coolant gauge. Nothing to do with the ECU file: the used ECU came from a car with a different cluster configuration and the CAN data mismatch confused the cluster. Coding the cluster with VCDS sorted it.

One more thing worth saying in front of the customer. Removing the immobiliser function on a road car in the EU is a modification some inspectors and insurers will ask about. The file does what it does; the paperwork is on you.

Files are on the Simos 3PE model page; if you’d rather send your own read, use the request form with the full label number. The other Simos generations (3.3A, 7.1, 9.1) have their own pages under VW and Skoda.