Peugeot 406: "ECU Not Found" Error - Fix

Yesterday, I tried to read the existing error codes from a 1999 Peugeot 406. I quickly located the OBD port, and the automatic protocol search ran extensively, but it only stayed on the KWP2000 5-bit protocol for a short time before my OBD handheld displayed the message "ECU not found."

I've encountered this issue with the automatic log search before. However, it always helped to manually select the log file where the system stayed the longest. I did exactly that! After a short wait, the startup screen even appeared briefly, where you can start the diagnosis. However, I was immediately kicked out, and with subsequent attempts, I received alternating error messages such as "No connection to the control unit," "Control unit not found," or "Control unit defective."

"No connection to the control unit" was a common issue I encountered, for example, with the Skoda Octavia I, where it was impossible to establish a connection. Suzuki, Opel, or Toyota were generally not a problem, even though sometimes it took a lot of effort to find the connectors.


Meine Frage: Welches Protokoll ist fuer den Peugeot richtig bzw. weiss jemand, ob der Hersteller fremde Diagnosetechnik unterbindet?

Normally, this should be mandatory for every vehicle inspection, and the minimum requirement should be the ability to read the error memory. I can easily read the error memory of my 2006 206 HDI70.

For diesel vehicles, OBD2 became mandatory only from 2004, while for gasoline vehicles, it was mandatory from 2001. Before that, it's possible that only a proprietary manufacturer protocol was supported.

Diagnostic testers for vehicle inspections (AU/HU) are only used starting with the Euro3 standard and, to my knowledge, can only read out emission-related values.

It's likely that the 1999 406 is not yet OBD2/EOBD compliant.

Thank you for the quick response! I thought that if there's a suitable OBD connector, then there's also functional OBD functionality. If it's a manufacturer-specific system, then the OBD connector probably wouldn't fit - that's what I meant. I've learned something new again... :wink:

The 406 is a 2.0-liter model with 136 horsepower and an automatic transmission. It spent its first year in France with Hertz (a car rental company) and was then purchased by the current owner. Features like automatic climate control, automatic transmission, light and rain sensors, front and rear parking sensors, and the Bordeaux-colored leather interior were likely above average for its class and thus a selling point. And it was offered at a price comparable to a 3-year-old Golf.

Despite all the negative comments, the automatic climate control system, which is often problematic in similarly aged Peugeot cars, is still working perfectly. I actually searched for a long time to find my 206 without (automatic) climate control.


The reason I requested a diagnostic check for the 406 was that the owner mentioned the MIL (Malfunction Indicator Lamp) came on immediately after the brakes (discs and pads) were replaced. The workshop ruled out a connection, and I can't really imagine it being related either. The independent workshop that did the brake work only has standard OBD technology. So, it's not helpful; it seems we'll have to have it diagnosed by Peugeot.