[rev] Fiat Punto CNG ECU / Metatron disassembly

Some of the Fiat Puntos (~6-7 years ago) were shipped with CNG. This CNG system (4100120/PN 55204807) was manufactured by Metatron. Currently a friend with such a system had the problem that the CNG was not useable anymore - no CNG injection, no LEDs lit on the (ugly) user interface. The garage analysed and suggested to replace the CNG ECU. Prices vary from 700-1100 Euro for new ones.

So it's the time to disassemble and take a look inside ;-)

On the Metatron site (outdated version of Typo3 :) ) I just could find three quite useless PDFs about the three different systems they produced.

Let's start with the deattachment from the car. The ECU is attached with non-stainless screws, which are twice as long as needed, close to the battery in a provisional looking arrangement (like the complete system).

The controller itself seems to be closed by 5 screws and a membran on the other side. Unscrewing these screws is just 10% of the work to open it. Those screws seems to be there just to put pressure during production. The complete cover is glued with a kind of silicone. I suggest to break away the cover on both sides of the lower egdes (opposite side of the connector) and saw a cut underneath the connector. With some force it is then possible to open it. Probably this guarantess the waterproof level (and prevents repair).

On the right side are several voltage regulators (2x 5V, 1.2V, 3.3V, 12V). Below the big 5V regulator is a K-Line controller. At the bottom is a Freescale MCU with an external eeprom (probably for the car individual settings). In the middle seems to be a mixed-signal ASIC produced by AMS (Now I understand the insane price) and a CAN controller. On the left side are some FETs and close to it is a quad power driver IC L9338D from ST. Might be that this one is used to drive the injectors.

First step was to figure out the power pins. Looking inside some datasheets and connecting it to the car I could easily find out GND. Actually two GNDs are connected (Pins 27/28). One to the frame/cover and the golden frame around the PCB. Close to the golden frame you find two plus symbols. I think those are for the alignment during production and not related to the voltage level. The real 12V goes to pin 1. Reversing and checking a bit the regulators - there's a 5V regulator output connected to pin 2 for the outside world. In my case this does not provide 5V... ;-)

For debugging I bridged the FET (?) at the top right below the transient filter. Else no input voltage was provided to the defective 5V regulator. Probably there is another input that triggers this with the car keys.