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daviesto
Member Since: 18 May 2015
Location: Reading, Berks
Posts: 67
  
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Our MY12 has developed and intermittent fault where it won't crank. It's done it three times now since December. Ignition on, self test OK, press brake pedal (brake lights come and and "press brake pedal when starting" disappears from cluster), press start button....nothing. No cranking, no relay clicks, no error messages.
On the first two occasions the RAC got it started by holding down the start button and stamping on the brake pedal really hard. Our garage could not find any faults and no error codes through diag so we changed the brake pedal position sensor as the most likely fault, but the problem occurred again today. As before, I eventually got it started by holding down the starter button and stamping on the brake pedal REALLY hard.
So, given we've already changed the position sensor, does anyone have any other ideas as to cause?
Thanks in advance.
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 28th Jan 2017 1:18 pm |
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daviesto
Member Since: 18 May 2015
Location: Reading, Berks
Posts: 67
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Anyone know if brake servo pressure is part of the logic loop here or is brake pedal position the only input?
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| 28th Jan 2017 11:14 pm |
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daviesto
Member Since: 18 May 2015
Location: Reading, Berks
Posts: 67
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Really hoping someone can help point us in the right direction here. As an update, the car refused to start again today after my wife had popped out to the shops. No amount of pushing and shoving the brake pedal (our earlier assumption) would get it started. And then all of sudden, with very light brake pressure, it started.
So now I'm wondering whether it's connected with the brake signal at all. If the brake interlock is a simple yes or no logic, and the brake lights are on, plus the cluster display message disappears, that implies that the ECU is getting a "brakes on" signal. If I further assume that there is no kind of interlock for e.g. brake servo pressure, then maybe it's something else entirely. So where do we look? What other signals does the ECU need to allow it to start? Or maybe it is trying to start, and there's something the other side of the ECU (starter relay etc) that has an intermittent fault? My only hope at the moment is that I can persuade it to go wrong and stay wrong and then at least the garage has a chance of tracing it.
Any thoughts?
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| 30th Jan 2017 5:28 pm |
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discoteca
Member Since: 08 Mar 2010
Location: Warwickshire
Posts: 1477
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I was going to suggest that maybe the button itself could be faulty but given the ignition comes on then probably not.
However, I've never started a D4 in the way you describe (i.e. press for ignition on, depress brake, then press again for start). I normally jump in, put foot on brake pedal press button once and it all happens in one go. Just out of curiosity, when the fault shows itself, I wonder what would happen if you tried that technique? I.e ignition back off after no crank fault, foot on brake first, one press on button.
Sorry to not be of more help though 
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| 30th Jan 2017 5:39 pm |
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jonno1
Member Since: 16 Jun 2010
Location: SW London
Posts: 707
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Pretty certain there is a TSB for this as long as you can hear a faint click.
TSB LTB00561v4/2015
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| 30th Jan 2017 8:00 pm |
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discoteca
Member Since: 08 Mar 2010
Location: Warwickshire
Posts: 1477
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From the workshop manual:
OPERATION
The starter solenoid is energised by a signal from the ECM when the stop/start switch is pressed and the driver has depressed the brake pedal. When engine cranking is requested, the ECM checks that a valid key code has been received before granting the crank request.
Once engine cranking has been granted, the ECM energizes the starter motor relay located in the engine compartment fusebox. The closing of the starter motor relay contacts causes battery voltage to be applied to the starter motor solenoid.
The solenoid is energised and the pinion gear is pushed to engage with the flywheel ring gear. Simultaneously, the starter solenoid contacts close, causing current to flow into the motor brushes and armature which operates the motor. The armature rotational force is transferred to the engine’s ring gear through the pinion gear, rotates the flywheel and starts.
Troubleshooting suggests the following to be checked:
Symptom Possible Causes Action
The engine does not crank (starter motor does not turn)
Gear selector not in P or N position (vehicles with automatic transmission)
Battery
Starter relay
Invalid key code received by
Central Junction Box (CJB)
Harness/Connectors
Starter motor
Ignition switch
Generator
Transmission Control Module (TCM)
Engine Control Module (ECM)
Engine seized
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| 30th Jan 2017 8:57 pm |
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daviesto
Member Since: 18 May 2015
Location: Reading, Berks
Posts: 67
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jonno1 wrote:Pretty certain there is a TSB for this as long as you can hear a faint click.
TSB LTB00561v4/2015
Pretty sure there is no clicking but in fairness I was to busy swearing and shouting. I'll give it a careful listen next time it happens.
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| 30th Jan 2017 9:30 pm |
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daviesto
Member Since: 18 May 2015
Location: Reading, Berks
Posts: 67
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So I've been driving the car for three days now with no faults, gave it back to SWMBO today and it failed to start in the school car park after dropping the kids off!! Now shows "Engine System Fault" on dash when holding down start button. Didn't get any sensible judgement on whether there is a "clicking" noise or not. Fault cleared after about 30 minutes of trying and car running OK now. Booked in for next week.
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| 2nd Feb 2017 5:41 pm |
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daviesto
Member Since: 18 May 2015
Location: Reading, Berks
Posts: 67
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Solved. Loose connection to starter solenoid. Lesson I learnt....check the basics and don't assume something complicated has gone wrong
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| 9th Feb 2017 7:39 pm |
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