2000 550 maranello - intermittent no start

Helping my friend diagnose an intermittent no start on his 550.

The car has been to multiple repair facilities and no one was able to diagnose it properly.

Issue is as follows: the vehicle will not start sometimes, it will always crank once the alarm is disabled (using the red, master fob) but sometimes would not fire.

This usually happens after the car has been left overnight, I noticed that when it doesn't start, the check engine light isn't lit on the cluster and there is a slow down message.
Cycling the key on and off a few times, check engine light is lit, wait a few seconds, "check ok", vehicle will crank and start.

I checked all the inputs (constant power, switched power and grounds) to both M5.2s on each side and they're ok.

I checked the two injection relays, on the control side they receive constant power from the fusebox and a switched ground from the ECUs once the key is turned to the on position.

I found that the switched ground to these relays is consistent with the behavior of the vehicle.. when the there is no check engine light on the cluster, the ECUs do not ground the relays and the vehicle does not start.

From my understanding, the immobilizer on this vehicle will only kill the starter, the ECUs should still power up correctly (check engine light) should be lit with the key on, engine off. I don't think it's an immobilizer issue.

To me it seems like an intermittent failure of the M5.2s, perhaps something with the power circuitry, faulty passives etc..

Has anyone experienced these issue? Any M5.2 gurus?

Any help will be greatly appreciated.

 

Thank you for your reply.

The car does have an OBD2 port, and as I stated, I know the ecus booted up correctly once the check engine light is lit (key on engine off) then there is also communication via a scan tool.

Thanks for the great info, the Slow Down message only happens when the ECUs fail to power up. All the relays have been replaced and the car has a GT car parts reman fuse box. The car behaves the same with the thermocouple ECUs unplugged.

What you inferred corresponds with my findings.

I'm leaning towards a Motronic failure, I don't know these well enough but must be some passive in the power circuitry. I don't know if these have electrolytic caps and perhaps they leaked? Maybe an oscillator issue?

I'm not sure what else will prevent the Motronic from booting and grouding the ECUs relays.

I only have the horrible factory diagrams, I will greatly appreciate anything other than the factory ones.

Thank you!

 

Thank you, it's definitely not a fuel supply issue, there is also no ignition when the Motronics do not power up and ground the ECUs relay.

The car runs amazingly once the ECUs are awake.

Also, sometimes even after a few days, turn the key on, CEL on = fires right up and runs beautifully.

Other days, no CEL with ignition on, and a no start condition.

I inspected both ECUs connectors when I was testing inputs to them, no signs of corrosion whatsoever. The connectors are very clean, as per the pins.. the female sides on the harness connector have an awful design I think, I tried to squeeze each pin gently to ensure a proper connection to the ECU male pins.
I like the idea about replacing them anyways, any good source for these?

I attached a picture showing the connector on the driver side, it's clean, same goes for the passenger side.

Image Unavailable, Please Login

 

Thanks for the reply.

We are using Leonardo for diagnsotics.

I doubt an SD3 will be more useful at this point as it seems to be a wiring issue or hardware failing.

 

Small update, replaced injection relays, now have terminal 87 output from both consistently, meaning motronics grounding the relays.

Check Engine light still coming on intermittently.

Noticed whenever no CEL (and obviously no start), ASR message is on.

Almost like a can bus issue where the ASR kills the bus or something or the motronics aren't fully powering up.

Wondering if Qavion may have a diagram for the ASR system and/or full CAN BUS plan.

Thank you

 

Thank you for your reply.

Would you mind expanding a little?

What was your exact issue? Was your CEL coming on intermittently when the ignition was switched on? With CEL car would fire, run normally? No CEL with key on = crank no start?

I was under the impression the alarm on this car only kills the starter, I "proved" it by getting a CEL with the alarm armed, but I couldn't crank the engine.

Please share more if you can.

Thanks.

 

Thank you!

Will scope the bus when I have more time to spend with it.

BTW the lack of CEL is always due to the ground from the RH motronic, bulb gets power from terminal 87 of the RH motronic relay, but it seems like the ECU fails to power up correctly (or missing some handshake with the alarm module over the bus) to ground the bulb and complete boot.. the lack of SI is the main challenge and I'm very grateful to all of the ones contributed.

I know some Alfas that used the same M5.2s would fail to power up if the alarm wasn't happy, if this system works the same, I guess I should investigate the alarm more.

If it is the alarm module, I wonder what will make it act up so intermittently.. I will first verify the inputs to it and make sure all are there, maybe this is the module failing to wake up / missing terminal 15 signal sometimes?

In case all the inputs are there and the failure is internal, I will see if I can spot which IC(s) store the immo data and perhaps will try and clone it to a donor module.. from previous experience with bosch systems, immo data is usually on an external eeprom and not internal to the mcu but I don't know if that's the case here as well.

I will make sure to update if I make progress.

 

Thanks.

I made a backup of both motronics before all the diagnostics, I was able to obtain the pin code and verified it by disabling the alarm with the pin I extracted using the key and ignition switch.

I need to verify all the inputs to the alarm module before attempting anything else, as there wasnt a difference to the CEL behavior with the alarm armed / disarmed I didn't thinker with it extensively.

As far as cloning, I was referring to the alarm ecu. I don't know what memory is in there as of now, knowing bosch systems from that era, most likely an HC05 or a custom chipset with a soic8 eeprom to store the immo data itself or neither.. I'm hoping to find a lack of some input to the module rather than a faulty module.

I wasn't familiar with immofixer, maybe he can provide insight as to whether or not a faulty alarm module would stop the motronic from booting up. If he can confirm it and has a solution then we will gladly ship the modules to him for a resolution. my extensive effort to diagnose this issue properly is simply because the vehicle has been to professional repair facilities that ran out of ideas and parts to throw at it.. previous facility also mailed out both ecus and immo modules to the only NA company that specializes in them just to get them back in the same condition without a solution.