Thank you everyone for your posts. Was that bet made on a 456M or 456? Is it a possibility that the 2 ECU versions output to be PWM on one model and DC voltage on the other? When cycling ignition switch on/off - there is a momentary voltage reading measuring across the ECU outputs. Waiting to borrow a handheld oscilloscope to further confirm. Yes, 100% duty condition was the intention. Hopefully didn't burn it out with 12V. Incidentally bench tested the old servotronic with 12V. It didn't react nor did i see any smoke, which led me to believe the unit was bad. How much resistance should be expected across the terminals on a solenoid like this? The servotronic (spoolvalve/TC) is a new unit. Harness from ECU output to spool valve Continuity test OK. I thought as a safety feature should PS ECU or power failure occur, that the spool valve would automatically set itself in a position of min assist (in case failure occurred @ 200kph.) If the opposite were true, then then this car's PS problem is not a software issue. Today the harness was unplugged/open circuit and had to move the car. There was a few moments when there was power assist! The pump is new. The rack works mechanically and isn't leaking externally. Is it possible an internal seal/rings is bad, allowing high pressure straight back into low pressure or some kind of blockage in the lines?
Just found this info from a BMW forum. Same 6V rated spool valve should measure 8.5ohms. They use 9V batts to test. I will do the same test/measurement and report back. https://www.bimmerfest.com/forums/showthread.php?t=1258146
It was a 550 steering ECU, but I suspect since your rack has the same Servotronic spool valve as our 550's, then the signals are similar. The ECU's are just packaged differently. Didn't realize you'd already replaced the spool valve. This is indeed puzzling. It'll be interesting to see if your measurement of the valve solenoid's resistance is the same as reported on the BMW forum.
Apologies for delayed response. Been so busy, not had time to post. Happy Holidays Everyone! Purchased a new Solenoid - Tested Ohm 7.9~8.1 with DMM. Internet research mentions spec Ohm on this BMW solenoid should be 8.5Ohm. - Both original solenoid & replacement solenoid tested with 7.9~8.1 Ohm reading. (both these solenoids had been connected to 12V) - If Ohm tests check within spec, could the solenoid still be damaged? Good Friend came by to help with O-Scope. - Speed signal is fine as seen in images, as speed changes so does frequency of PWM signal. Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login BUT... Still NO output from the ECU! - Both orig and brand new ECU's tested same. - Both ECU's double checked for 12V & Ground - Both ECU's produce a blip[ reading voltage output when first cycling ignition. So... still stumped. - Tests above were run with the (replacement) solenoid connected with ECU (just in case it needed to see a resistance to work). O-scope took readings with wires "T'd" into pos/neg wires. - Not sure what is the best practical test route from here... Next: Find a voltage pulse generator with enough juice to test the solenoids for movement. Mechanical Failure? - At one point, whilst driving the car @ car park speeds, there was about 15 seconds of marginal power steering! This was with the solenoid detached. Even with the solenoid detached, should there be at least some power assist? Electronics aside (there may be an issue here also), I wonder if the rack is failed internally, pressure is passing straight from high to low side?
Quite baffling. I do find it hard to believe that a mechanical problem would stop the ECU operating. There aren't any wires for position feeback circuit from the solenoid (to tell the ECU that it's not doing its job), so you expect it to continue ouputting the appropriate signal. Circuits, however, do behave differently under load. Have you, for example, checked the input voltage to the ECU during operation or just with the ECU disconnected? Maybe there is a bad splice in the green-white power wire? Or try testing the voltage with the ECU disconnected with a test lamp rather than a multimeter. Those test probes with built-in lights seem to be useful in loading up circuits. Anyway, it's good to hear you're still persisting. Good luck!
When I was developing & testing new output curves for the 550 Steering ECU's I had the ECU's on the bench with an 8 ohm resistor connected across their output terminals and I used a variable frequency signal generator to simulate the speed signal. What I know to be true is that when I supplied +12 to the "15" terminal of the steering ECU, grounded the "31" terminal, and varied the frequency of the signal generator at the "V" terminal, I was able to measure the specified range of currents at the ECU output. Note, I said I measured current, not voltage. So you must have either the solenoid valve or a dummy resistor across the ECU output terminals, and you must be setup to measure current, not voltage, at the ECU output if you want to see the curves that Ferrari provide for this system. Again, all this was done with 550 Steering ECU's, not the 456 Steering ECU, but I'm sure the same procedure would work with the 456's steering ECU. This is truly confusing as it contradicts our understanding of how the system works. With the solenoid valve detached, there should not be "any" power assist available. So perhaps your conclusion that there's a mechanical issue, could be valid. I know you must be tired & frustrated with troubleshooting but I would completely reconnect the system again as it should be for normal operation, but tee your DC ammeter into the harness going to the solenoid valve so it's setup to measure DC current in that circuit, then test the system at idle without the car moving, and you should see around 600 milliamperes on your ammeter. If you don't see this, then confirm there is power and earth on terminals A3 & A2 of the ECU. This ECU should be outputting maximum current when it has power, the speed signal is connected, but showing zero speed, and the solenoid valve is connected. See the pic/illustration below for a description of the operation. Image Unavailable, Please Login
John, when testing on the bench, did you use the earth pin (A2) for the signal signal (earth) as well as the negative power terminal? I was thinking of investing in a square wave signal generator like this: https://www.ebay.com.au/i/401925687410? The amplitude of the output signal is the same as the input voltage. Just wondering if a 9 volt smoke alarm battery would work (the input to the steering module is supposed to be 0~8volts). Thanks!
Ian, yes I used A2 for both. That's a cute little signal generator! Wish I'd bought something like that instead of mine, which is a plug in type.
Cribbj - Thank you so much for posting this info and your advise. As you pointed out, erroneously measured for PWM and Voltage, rather than Current. Thank you to everyone following and commenting. Test Method: Shorter harness connected inside cabin, between the solenoid and solenoid ECU. This allowed solenoid to be physically monitored @ speeds. Results: 860 mA when stationary and drops to about 350 mA @ 100 km per hr. Results are in line with graph from Cribbj's post. Solenoid pulses felt and visual movement from inside ports @ speed. So... The electronic system is working properly. No change in power steering assist, zero @ any speed. Checked PS reservoir: The system was properly bled after replacing the PS pump. Bled with wheels off ground, after cycling - clear red fluid and no bubbles. At that initial point, no hint of power steering. After several rounds of testing however, the reservoir has become extremely aerated, pink in color. No pump noise. No external leaks. aeration is persistent, does not clear up after sitting. Replaced aerated fluid and bled until system was clear again. Same result, no assist and after repeated testing with wheels full load/weight on the ground - fluid becomes aerated again. Few theories - Hoping you guys can share thoughts here. 1) There's an air leak under pressure on suction side. Could this be coming from the suspension circuit? How does this explain zero power assist? 2) Blockage some where on pressure side that prevented full bleeding in first place & causing pressure drop. Are there any hoses suspect/common issues to check or valves in circuit that could jam and cause this? 3) Bad Pump? Pump sourced from reputable eurospares. Before the change, the old pump was noisy/intermittent PS assist. 4) Bad Rack? No significant external leaks. Could the rack be leaking high/low side causing pressure issue and possibly source of aeration? 5) Filter inside reservoir Fully submerged in fluid. Could blockage here cause symptoms described? Solenoid: As an aside - Results from 3 solenoids with the (C) being brand benchmark: A) the original solenoid did have correct ohms, but did not activate @ speed. B) 1st replacement solenoid is still working, after prolonged 12V testing (not advised, just reporting result). C) 2nd replacement solenoid same ohm reading and function as (B). - Just because ohms are with in spec, does not mean the solenoid is good. Thank you!
Seems like a mechanical failure, after all. Since the hydraulic system is shared with the suspension, which operates at a different pressure, do you also have problems in that system? Can it be, for instance, that the pump developed an internal leak between the power steering part (high pressure) to the suspension part (low pressure)? It doesn't quite explain the air, though??? Did you bleed with engine running?
Thanks for your reply. Intermittent warning light for the suspension but goes away after start up, and only see it may be once every 15 times cold start. Suspension height is fine. Bled with engine running and wheels off ground. Even if there was a slight leak, would still expect there to be some power assist.
If you can manually steer the car OK, and you're not feeling any binding in the rack, I would be suspicious of the new pump. If you have access to a P/S test rig, put your pump on the tester and see if it's developing pressure. If it's making good pressure, then it has to be the rack. Surely there must be some P/S or hydraulic specialists in Hong Kong?
Hong Kong is a small market, there are no true PS/Hydraulic specialists and certainly not many independents that are familiar enough with this particulars of this system. Agreed with Cribbj's suggestion seems reasonable next step to rule out the pressure issue. We could rig up a test rig. Should it be placed in front or behind the damper reducer. This part is described in detailed in the following link: https://www.ferrarichat.com/forum/threads/456-power-steering-suspension-pump-and-lines.536363/ And what pressure range should we be looking for? Might as well replace the pressure line to rack from pump whilst at it. I wonder if the reducer is plugged up. Has anyone overhauled this hose section by removing/re-crimping the reducer? Aeration could be coming from the return lines from shock portion of the damper system.
I would suggest using fittings & putting a Tee section in either at the pump or at the rack, unless you really want to replace that high pressure hose with the dampner, and they're pretty expensive. Last I remember they were around 600 USD? I've forgotten how much pressure that hose sees, but I vaguely recollect 800 to 1000 psi? Someone jump in & correct me if you know better. I think Brian or another pro mentioned they were able to salvage the dampner and put it back in a new hose. I don't see how because it's already crimped on both ends, but pro's have ways of doing things that we mere mortals don't know about......
Thanks to contributions of members here, have finally solved the issue. Replaced all hoses: Image Unavailable, Please Login Re-crimped the reducer and re-used ends to make a new hose section locally. Fabricated an adapter for pressure gauge for banjo bolt. The pump after bleeding was only making 12-21psi. Replaced it with the old pump and pressure blew out the gauge (maxes out at 100psi) and Voila - Got power steering! In Summary: Mis-diagnosed bad rack solenoid for a failing PS pump. Replaced with a rebuilt unit, that was bad out of the box.
Congratulations DrivenHK! So pleased to learn that you've sorted it finally. This thread has been in the back of my head for months now, wondering what could possibly be wrong with your P/S system, making it behave as you described. Glad your logical fault finding approach paid off and you'll soon be able to drive your car normally.
A lack of understanding of Greek, perhaps.... and most definitely "Ferrari" In which language? Speed signal is standard for speed signal in english and I thought Italian for speed was velocita? Using Google translate, tachometer translates as tachometro in Italian. This was my first contact with the Tach- words (in the WSM wiring diagrams). Image Unavailable, Please Login Not finding a translation for CONTAG, I firstly assumed TACHIM was the Tacho. Of course, the location of the instrument is the first clue as to its real meaning. Anyway, we digress.
