ECU Guides

Delphi DCM3.5 Immo Off and Virgin: Peugeot, Citroen and Ford 1.6 HDi / TDCi Euro 5 ECU Guide

29 September 2026 2 min read

The Delphi DCM3.5 is the engine ECU of the 8-valve 1.6 HDi (DV6D / DV6DTED, 92 hp) Euro 5 engine fitted from 2010 to the Peugeot 207, 208, 308, 3008, Partner, Citroen C3, C4, DS3, Berlingo and the Ford Fiesta, Focus and C-Max 1.6 TDCi 95 hp, as well as some Mini One D and Volvo V40 D2 versions. Its cousins DCM3.4 (2.0 HDi) and DCM3.7 share the design. Requests for DCM3.5 immo off and virgin files usually come after a BSI failure or a second-hand ECU purchase.

Immobilizer behaviour

On PSA the BSI holds the key data and the ECU stores the pairing; on Ford it is PATS with the cluster. A mismatched DCM3.5 cranks without starting, and Diagbox reports P1517 / immobilizer: ECU not coded. Note that PSA cars with a dead BSI also lose the fuel pump control, so an immo off file alone is not always enough — the BSI must at least power the pump.

Immo off or virgin?

  • Virgin — the ECU is reset to “not coded”; Diagbox (PSA) or IDS/FORScan (Ford) then codes it to the car. This keeps everything original, including the anti-theft function.
  • Immo off — the DCM3.5 starts with any key and without the BSI code. For engine swaps, bench engines and vehicles with an aftermarket BSI replacement.
  • Original — restores a bricked or badly tuned unit; the immobilizer pairing is unchanged.

Reading the DCM3.5

  1. Bench: KTAG and Flex read the DCM3.5 (TriCore TC1767) through the connector, including the immobilizer area. This is the preferred method.
  2. OBD: KESS V2 reads and writes most DCM3.5 software versions over OBD; useful when only a stock-file restore is needed.
  3. Take the Delphi number 28xxxxxx and the PSA 96xxxxxx80 / Ford 9M5A-12A650-xx number from the label; the software number must match.

After the write

Virgin: run the ECU coding with the vehicle key data present, then clear codes. Immo off: the engine starts straight away. If not, check the fuel lift pump fuse in the BSI/BSM and the injector connectors — on the DV6D the pump is BSI-controlled and a BSI fault stops fuel delivery regardless of the ECU file.

See DCM3.5 files and the related DCM3.4 and DCM3.7AP, or browse Peugeot, Citroen and Ford. For a version that is not listed, use the file request form with your original read.

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