Euro 550 OBD plug . Yes it is there and I have found it.

RE: 550 and 575, In order to read both ECUs the immobilizer must activated with the ignition on. If you just turn the ignition on without engaging the immobilizer only the left (slave) ECU can be accessed.

I wasn't aware of this and that lack of knowledge cost me many hours and considerable dollars

 

Regarding coolant temp sensors, if one bank is ok, then the coolant temp sensor should be ok as only one sensor is used for engine management (on both banks). If the right ECU is failing to send data to the other ECU either because of an ECU issue or a wiring issue, I think this would have been spotted earlier. I guess it depends on how the data is transmitted from one bank to the other (data bus or discrete wiring).

 

activated or deactivated?

 

Good point, I meant to say you must disarm the immobilizer

 

yes - i have the 3 pin to OB2 adapter with the red and black power wires coming out. So I connect those to a power source as well as the 3 pin connector. The scanner I have tries to read the code but doesnt get anything - feels like a software mismatch. but i will try again, ensure the ignition is on and immobiliser off, and try with my new fuseboard as the old one is a bit dodgy.....

 

The temperature sensors in the left and right coolant manifolds trigger the radiator fans. The sensor in the left manifold is the primary sensor and turns them on at a certain temperature. If that sensor fails, the sensor in the right manifold acts as a backup and turns the fans on but at a higher temperature, (220F I think). You know your primary sensor is bad when your fans turn on, but at a higher temp. Happened to me. My fans normally turn on before the half way mark on the gauge, then one day all of a sudden they didn’t turn on until past the half way mark. Left side sensor died. The 3rd temp sensor (the expensive one) signals the temp gauge and can also trigger the multi function display if the coolant gets too hot, I think 235F.

 

I bought a Fiat 3 pin OBD2 adaptor only to find the 3 pin connector will not mate with the Ferrari 3 pin connector. After a few fails I have ordered another connector and will try again when it comes. I'm just curious to see if I can access one ECU at a time via the 3 pin connector. Some are calling it a "serial connection" I don't know it's actual name but I suspect it is for connecting a SD tool, or maybe it's an ALDL connector
ALDL= Assembly Line Diagnostic Link

 

The same wiring goes to the OBD2 port on US cars. Perhaps it depends on the ECU what kind of data is transmitted?

 

I'll know more when I get my ECU's back sometime next week.

 

Sounds similar to this switch, but I don't know why a 550 would have a 2.7-style ECU test switch.

https://www.ferrarichat.com/forum/threads/electrical-wonders.626470/#post-147364844

Do you have a switch on both sides?

 

The data cable goes from one ECU to the other ECU (via wiring splices). By disconnecting that 3 pin data connector and plugging in your scanner, you won't be able to get data from the passenger side (at the same time). Only a proper OBD2 plug can do this as it doesn't interrupt the circuit (It's spliced to both ECUs)

So the sensor is reading hotter than it should be. Remember the data from the left sensor is not used by engine management. It's only used for fan control. The right sensor is used by both banks (somehow) and fan emergency backup.

The -40C means the ECU can't read the temperature data (or it's very, very cold). In message #7 in this thread, the -40C engine coolant temperature (ECT) reading on the Left ECU may only be that value because the ECU can't read the data as the left temperature sensor isn't hooked up to the ECU (because the left sensor is only hooked up to the HVAC system). The scanner may not be smart enough to look for the temperature data being sent from the Right ECU (right sensor) to the Left ECU (on the left/right bank interface plug... or however the data is being shared).

A driveability problem due to temperature would only be due to temperature sensor errors on the right side (but you know that is ok, as it gave a reading of 15C... assuming it was 15C that day).

I'm not really sure what it does, also. Someone just mentioned they had a switch in a similar location on his 456 which was hooked up to his ECU.

Apart from those small leaks, I'm not sure what else could be affecting the engine management system.

Are your fans so effective that they are cooling the coolant temperature so much that the right sensor is getting a low reading? Anyway, at some point, you'll have to change the left sensor because the fans are coming on too soon.

 

Sorry, I misinterpreted your first statement. I thought the fans were starting early. I haven't looked at a 550 temperature gauge recently. If they are starting too late, then the emergency fan system may be operating (using the right sensor). The right sensor is used for engine management on both banks.

Possibly a problem with the bank interconnect wiring or plug. However, I was looking at photos of 550 harnesses and I couldn't find the 12 pin (interconnect) plug as shown in the wiring diagrams. I can't figure out how the ECUs talk to each other (unless it is via the 3 pin "Fiat" plug).

Here's an advertisement for a used harness:

https://www.ebay.com/itm/Ferrari-550-RH-Engine-Wiring-Harness-USED-P-N-171394-/402336559010

I see the large rectangular plug (which has 21 pins in 3 rows) which interfaces with the rest of the car and a strange 8? pin rectangular plug which is not in any of the wiring diagrams.

Note the two plugs near the ECU. Do you have both of these?

Sorry... it's late at night here and I'm losing concentration. I'll have to re-read your message tomorrow, but when you say you disconnected the MAF... and the scanner shows zero, is the MAF on the same side of the car as the ECU or the opposite side?

(edit) Can you find that rectangular 8(?) pin plug in your own car and see if it has more than 8 pins?

 

Just to clarify, the 21 pin plug is on the left, next to the ECU plug. The 8 pin plug is on the far right near the circular (injectors) plug.

 

Thanks! Previously I wasn't sure what side MAF data we were looking at. So even though the MAFs are wired directly to their same side ECUs, the MAF data must be sent to the opposite ECU on the mysterious interconnect wiring (i.e. not on the 3 pin plug, because that is disconnected).

The 21 pin plug is in the footwell (both ECUs have this wiring). If you look at the photo of the harness, you will see a rubber seal. Everything on the ECU side of the seal will be in the cabin. The other side will be in the engine bay.

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There's the right side harness. Here's where it gets confusing. I looked at photos of the left side harness and it doesn't appear to have a male 8 pin rectangular plug counterpart.

There is a Ferrari label on the ECU harness near the ECU. Can you read the part number of your left and right harness?

Anyway, I think I'm digressing. We know that the ECUs are sending data to each other (via a CAN Bus). If the data is reading high or low, datalines problems cannot cause this. Either the wiring from the MAF on the right hand side to the Right ECU is faulty OR the Right ECU is not converting the analog MAF data to digital data correctly OR the Left ECU is not decoding the digital data correctly OR... there is an engine problem.

 

Find the circular plug and go back 10~20 cm. There will be 5 or 6 sections branching out. The smallest one is an earth.

 

If you have some spare time, can you see if that 2 wire plug near the ECU is plugged into anything?

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Your harness may or may not have this plug. It's not shown in the wiring diagrams.

 

It's the female side of the 3 pin OBD2 connector. They are connected together, two wires on the female, three on the male.

Some have called it a "serial connector". If it is disconnected the data link to the scanner is interrupted
Look at any of the other pictures of that harness on eBay, most pics show it connected

Ferrari 550, LH, Left Engine Wiring Harness, Used, P/N 173940 | eBay

 

ooops... of course..... I see now that the 2 wire plug doesn't actually go to the ECU*, but is wired to the large 21 pin connector.

* except when it is plugged into the 3 wire plug, of course.

Wiring diagram

https://www.dropbox.com/t/ocVrSeVAp6lXMp5R

 

Robbe, I'm not sure how safe or reliable it is to check the resistance of the wiring on the MAF plugs (male or female). Your resistance checker is introducing a small voltage into the circuit which may affect or damage MAF or ECU circuits.

Not sure what all the components are in this typical MAF circuit, but I see a transistor and a signal amplifier

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pin 1) earth
pin 2) signal from the ECU to turn on the MAF
pin 3) 12volts power
pin 4) MAF output signal.

 

If you're checking the MAF to ECU pins and there is a discrepancy, then this would suggest a wiring fault or ECU fault. Can you do wiring resistance checks between the MAF and ECU? (with the ECU disconnected).

MAF plug pin 1 (black wire) should show a short circuit (low ohms) to ECU plug sockets 6, 28 and 34. It should also show a short to the engine block.
MAF plug pin 2 (red/green wire) should show a short circuit to ECU plug socket 45
MAF plug pin 3 (green wire) should show a short circuit to ECU plug socket 54
MAF plug pin 4 (red/black wire) should show a short circuit to ECU plug socket 17

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Make sure that none of the wires are shorted to each other.

(EDIT... my earlier mini diagram shows the wrong ECU pin number on MAF pin 2)

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When you short your multimeter probes together (in resistance mode), what reading do you get?

 

Regarding the ECU to ECU interconnect wiring, it looks like these are definitely the plugs:

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The Ferrari 456 also has 8 pin plugs.

I don't know why the 550 wiring diagrams show a 12 pin plug with 9 wires on it.

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I can't modify my coloured diagrams until I figure out what to do with the 9th wire.

If you find that plug, maybe you can tell me what the wire colours are

Perhaps I'm just going blind and there are 12 pins?