neiloakley Posted August 15, 2014 Share Posted August 15, 2014 I have a problem with my 2007 TDV8 Vogue. The power steering is heavier than it should be (and compared to my other TDV8 vogue). Had the car a month and issue has been there since I bought it (it was very cheap so couldn't say no). Symptoms: Steering is heavy regardless of engine speed Road speed seems to make no difference (although less noticeable at higher speed due to less steering input required) Very occasionally, the steering will be light after start up but not managed to link it to any other event that would cause it to go light Sometimes when starting, the instrument cluster turns off for a split second and then goes through it's start up procedure when the engine is started. Not sure if this is related Things Tried: New servotronic valve New BCU (or GEM as they are known on the 07MY). Hours of internet forum searching. I understand that on models up to 2007, the servotronic valve was controlled by the BCU and would open and close depending on a speed signal the BCU got from the ABS ECU. However reading the 2007MY workshop manual, the BCU has now been renamed the GEM (general electronics module) and the description of it's function makes no mention of the Servotronic valve. I was hoping to find some wiring diagrams to confirm that. One other 'specialist' said the steering column joints may be stiff, but that doesn't explain why it would go light occasionally. I'm unsure if the quirky instrument cluster is related or not, it could cause a CAN BUS fault, but on the 06MY the speed signal from the ABS ECU to the BCU was hardwired and did not use CANBUS, and the servotronic valve was hardwired to the BCU so cant see that would cause the issue. One person on the web fixed their instrument cluster with a new ignition switch (was only providing 9v output on the switched live during cranking hence the instrument cluster went down, cranking power to the engine was 12.6v). I will check the ignition switch this weekend, but dont hold out hope of that fixing my steering issue. Anyone have any ideas, or come across the issue before? There is a serious drink (or cash alternative) to anyone that comes up with the solution!!!!! Thanks in advance Neil Quote Link to comment Share on other sites More sharing options...
Ally V8 Posted August 17, 2014 Share Posted August 17, 2014 In a way you are in a good position in having a similar fully functioning car car to test from. I had to deal with a similar fault on an 04 L322 a while back.It would give power assistance perfectly until about 3 secs after reaching about 30mph... That one turned out to be a faulty BCU.The info on Topix is limited and I sorted that one out with the help af my oscilloscope.What happened was the servotronic valve was fed battery voltage across it until 30 mph was reached,it then started to pulse the feed to it as a square wave.This progressively opened the valve lessening the power assistance as speed increased. For your car I would do two things,first check the output pressure from the pump.(You could swop it from your other car if hooking a gauge up is too much trouble)Secondly tap into the wires right next to the servotronic valve so you can monitor the feed to it.Probably best done by sticking a pin through the wire and taping it up,then use cable ties to get extension wires back into the car.A decent multimeter will be good enough to show whats happening.After the repairs are completed clear nail varnish on the pierced section of wire,then self amalgamating tape are a good way to re-weather proof the wires. Siezed column uj's are not common on L322's and they usually show as being stiff for part rotation then free up as they continue to rotate,going stiff again as they get to the same bit - if that makes sense.... Quote Link to comment Share on other sites More sharing options...
simonr Posted August 17, 2014 Share Posted August 17, 2014 The Servotronic valve, as Ally V8 mentioned is fed with what's known as a PWM or Pulse Width Modulated signal. It changes the ratio of the time the valve stays open versus closed. This happens quite fast so it just feels like the valve is partially open - and the ecu can vary the timings to give everything from full to no power steering. Try disconnecting the valve from the wiring harness. This should close the valve and give you full PAS. If this works, you know that the steering pump, rack and valve are working OK. _____-______-_____-_____-_____ = What the trace should look like for 0 mph ------- _-------- _-------- _------ _------ = No PAS - valve fully open -----___-----___-----___-----___-----__ = Valve 50% open / half PAS You really need a scope to see if the pulse train going to the valve looks appropriate - switching between 0v and somewhere close to 12v. If the pulses look OK - and you can see both 0v and 12v(ish) then the GEM may be OK. If it's stuck at 12v (no pulses), I would suspect the GEM is either broken or not interpreting the CAN signal telling it the road speed correctly - though if the latter, I would expect it to sit at 0v, the equivalent of 0 mph. If the pulses are not going to 0v (I suspect this may be the case), the valve is not quite able to close - then the transistor (MOSFET) that drives the valve inside the GEM has likely fizzed itself. This may well be repairable. You are unlikely to be able to diagnose this with even a good multimeter as the pulses are too fast for the meter to resolve. Find someone locally who has a scopemeter. Many of the car test systems include a scope function. Either way, the GEM is the most likely problem. CANBUS problems would likely cause many other faults - but it's rare for the CAN Transceivers to go faulty. The Servotronic valve (for the benefit of anyone else) is easy to test. Connect 12v to the valve and it should have no PAS. Disconnect and it should have full PAS. Worth poking around with a few bits of wire before replacing. Si Quote Link to comment Share on other sites More sharing options...
Ally V8 Posted August 17, 2014 Share Posted August 17, 2014 I apologise if I'm wrong,but I think you will find that the valve gets closed by full battery voltage at less than 30 mph,so disconnecting it would the least assistance. Quote Link to comment Share on other sites More sharing options...
simonr Posted August 17, 2014 Share Posted August 17, 2014 You may well be right - it is possible that it works the other way round, so the valve closes when power is applied rather than opened but the convention is to open (allow flow) with power applied to the solenoid. The diagnosis method still holds if this is the case though - just the result of applying power directly to the solenoid is reversed. Si Quote Link to comment Share on other sites More sharing options...
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