Hi all, I have a SDL light in my 97 5.2 motronic euro spec. As it starts to flash from cold, but does not go solid, and I have no CEL, I never really bothered to fix it (I had other issues to fix with this car, like the lhs fan, but that is ok now) So I read the extensive report from Jevs about the Cat Ecu's , which helps enormously to examine what has gone wrong. Great post. But now for the funny part: - when fed 12V to each cat (bypass directly from battery) ( I have 2 cats, euro version) , the output at ambient temp is 0.68 v and 0.7 v. So that sounds good, and no need for the motronic to let that SDL flash. The cat Ecu's are at least not giving a signal of over 5V, so the cause of the SDL is not in that direction. - the cat ecu's also receive 12v directly when the key is turned (actually 14v, engine not running) , and ground/earth (GRD) resistance checked out fine on both sides. So the power supply in action is good as well. - the resistance of the connector+line+motronic is 317k Ohms on both sides, which is near the 312k ohms in the investigation of Jevs. So sounds ok as well So the cat ecu's work as they should, there is no short or open circuit on the connection to the single motronic, so the 0.7v reaches the motronic 5.2 from both sides. Why then do I have a flashing SDL from cold... Do I need to clear a code, even if I do not have a CEL at all?
I don't know how your reading the voltage outputs of the SDECU but that is the correct way to diagnose the problem. If you have tapped the outputs or backprobed them, run a long lead into the cabin of the car from both locations and check the outputs real time. I have seen spikes caused by thermocouple shorts set off sdl and to low of voltage at startup will also. I have some aftermarket transmitters installed in my car that start at .2v when cold and I have flashing sdl at startup that go away after awhile. Put your dvom on each output and watch it from cold. It's should start at .5v and gradually rise to around 3v when hot with not spiking.
Do you know if the SDL has a memory? I mean, once a voltage too low or too high started the DSL flashing, does it stop flashing when the voltage is within range again? Because I have read of a SDL going away again (like with you) , but also that once started, it will remain flashing until the engine power is turned off again. If it goes away, the initial spike or too low a voltage cannot be the cause of the SDL keeping on flashing...
In my case it goes away without having to turn the car off. It does not go away immediately on the voltage reaching a normal state and it also doesn't go away the same every time. There must be some parameters in the motronic that need to be met over time or something. It is not an absolute relationship. There are a ton of electronics on board the sdecu beyond what a simple voltage transmitter has and possibly some of the subjectivity is within the SDECU itself. Regardless, I have found that if you get the output to start at .5v and get no spikes, you should have no sdl. Watch your voltage realtime through some cycles and see if you don't have some spiking issue. I have a video of one of mine doing that at idle that I will try and find and post.
I set up the connections to control the cat ecu at startup. Contact off: 0.0 V. Contact turned to ON: 0.61V Starting: dropped to 0.59V, then rose again to first 0.61V, then within seconds to 0.65V There it stayed for a few minutes, while the car was warming up. Then it slowly rose to 0.66V, 0.67V up to 0.71V (water temp around 80 degrees C or so) where I was convinced that it was working as it should. The other side gave the same pattern, but for the slightly higher starting temp and thus starting voltage. So I am still puzzled.
Have you tried unplugging the TCUs and mimicking the signal to the ECU with a 1.5 V battery? If you do that and still get a flashing SDL if would suggest that it's something with the ECUs, nit the TCUs. If so, I would then clear the ECUs and see what happens.
I just tried it, thanks. A penlight AA battery, connected to Ground and Signal on the connector, one on each side. Measured 2.03 V to the ECU on one side, and 2.05 on the other. So the ECU should consider that in range. Unfortunately after starting, the SDL still blinks. We can rule out the vescovini cat-ecu's for sure now. So do I have a bad main ECU? or could it be something simple as a loose pin in the ECU connection? As far as I know I do not have other symptoms, but then the resistance test would not have shown the 317k Ohms...
Hum. How are you getting a 2 V reading from a 1.5V battery? It you haven't tried it, I would do a batter disconnect, then reconnect, then connect an OBD II reader and do an OBD II reset. Then start the car. If it's still flashing after that I haven't got a clue.
Thanks, will try that tomorrow. (by the way, the batteries were Ikea 1.5V AA penlites, maybe Ikea is giving 0.5V away for free like their breakfast, to lure people in )
Have you tried checking OBDII codes? I had an SDL from an electrical connection issue. No more SDL after I fixed the connections and cleared the codes.
Check your meter as well. Mine that I have had for 20 years just went and I pulled half of the wiring in my car hauler apart before I realized it was the meter. First time that has happened, next time I will check meter first.
The batteries were new, and gave 2.03V and 2.05V. The output from the vescovini's in normal starting conditions was around 0.6. So even if my meter was 0.6 optimistic, the batteries would have given 1.4V in reality which would have been good enough to satisfy the ecu...but it didn't. Now I will first have to make the OBD scanner that I have, work with the car. (known issue, euro car 3 pin connector OBD, and reader has the full 30 or so connector pins) Maybe instead of ordering a special connector and having to wait a week, I can make it myself, there is info on this on the forum, I will have a go at it.
Clear the codes before you do anything more. I've chased a few of these and solved all of them before. It sounds as if your cat ECU's are ok, but they only way to be 100% sure is to scope the output (a meter can't show intermittent spikes or transients on the signal wire in real time which is a failure mode of the vescovini boxes). Be careful applying voltage to your main engine ECU inputs, if it's not broken that's a very good way to make it broken. Safer to use a 2v zener diode and a series ~1k resistor to clamp the pin with a reference voltage to ground. As it has an internal pull up to 5v the zener clamp is a safer way to get a known voltage on the pin. But, before you do any of this, clear those codes.
Yes, I think it is wise to first read and clear the codes, and then work on a sure way to get a known voltage. But another small setback, I can't get my OBD scanner/reader to work with my 355. I connected the 3 pin OBD to the correct 3 pins 5,7 and 15 on the scanner, but it gave a connecting error. Now it was a cheap 50 euro reader that gives connecting errors on more cars, so I will now have to look for a OBD reader that will work on the 355. I have posted the question about a working reader before a year ago, and I even got an answer, but I saw that too late, and the link in the answer was not working anymore. So does anybody know of a reader that will definately work, and that is available in Europe (ebay or so)? (a US item would takes another 2-3 weeks to arrive)
I use a KIWI 2 bluetooth reader in my US 96 OBD2 car. You can control it with a phone app. Does everything for me.
As I did not get the OBD scanner to work, I took a motronic from a 355 project that I plan to rebuild one day. That motronic was corroded, and open, so I had no faith what so ever, but installed it anyway. To my surprise, it worked, and the SDL is gone! So it definately is something in the other motronic, an error somewhere in it or maybe a code that needs to be cleared. The Ferrari part numbers where different between the both 5.2 motronics however, but both labelled 129 EU . The old one with the SDL was 176224 (not for USA, CDN, AUS etc) The "new" one now installed is also not for USA etc, but is specifically for Japan, Swiss, and Sweden. (which is not EU, except for Sweden) Does this mean that it might develop lower HP? Or any other aspects or reasons why I should not keep it in the car for the time being?
Now I have the car working SDL-less with the other motronic, I am not in a hurry anymore to get a scanner fast. So maybe I give that Kiwi thing a try even if it takes 2-3 weeks to arrive. You used the cigarette-lighter for 12V?
Powers through OBD2 port. I have no experience with euro cars, so I cant say how it will work for you. I like it because I can stream live data and record it. You cant monitor Cat ecu's but there is a lot of other stuff that is fun to watch. Coolant temp, fuel trim etc. I guess it is possible your new motronic is not showing a light because the code is still pending. After some time the car may throw the code is the problem isn't corrected. Most scanners will show "pending" codes. No way I could have diagnosed issues on my car without a scanner. Must have tool.
OP - i may have missed this while skimming the thread...did u look at your cat ECUs? When my SDL was acting up 5 yrs ago i checked them and they were black, with visible cracks in the epoxy, so i just replaced them with the updated green pot units. The black units are notoriously bad and by rule fail eventually. Didnt bother with any testing. They were about $200 apiece and it took an hour to change them. Havent seen an SDL since.
He's gone through thorough diagnosis of his issue and it doesn't look like it's the SDECUs. He's measured the output voltages and determined that his ecu are working as designed. Fortunately he didn't just throw $500 at the problem and buy new ecu. I think folks on here pointed him on the right track in getting a euro OBD setup and clearing any existing codes and monitoring from there.
Dr. Bob - Yes I understand that he went through the procedure in a methodical manner but I wonder if rudimentary testing will pick up intermittently faulty circuitry. After all, the faults are typically intermittent so one may not catch the problem at any given point in time. My point was that with the black potted ECUs, they will eventually fail if not failed already, so that money is going to be spent anyway. If the ECUs are green, then I fully agree that replacing with new units would be imprudent without ruling out other causes.
