Sometimes, the Auto Hold despite being engaged and showing green on dashboard doesn’t hold the car in place
BHPian Tmittal93 recently shared this with other enthusiasts.
I got my XUV 700 AX7L Petrol from Indraprastha Mahindra Delhi on 17 May 2023 after booking on 07 October 21. Glad as I could be, the car has started to show issues after driving merely 350Kms.
The major issue being problem with EPB and Auto Hold.
Now before I go in detail, i searched plenty about the issue but couldn’t find any discussion on same anywhere on net.
The problem arises during cold start and witnessed it first on 06 August and again on 09 August.
Once the car is parked and put in Park mode, the E-parking brake engages automatically, following which I turn off and exit the car.
However, when I cold start the car after 1-2 days, wearing seat belt, all doors closed, shift to D from Park, the car starts to move forward without me pressing the accelerator, while EPB is still engaged. The red light on EPB switch glows and the dashboard shows EPB still engaged. Yet the car starts to move forward. I have to press the brakes to stop it.
This only happens on cold start. Consecutive stop start, the car functions normally and does not move until I press the accelerator when D mode is engaged and EPB is still active.
Now, normally, once you enter the car, put on seat belt and close the doors, turn the car on and shift to D mode, press accelerator, the car automatically disengages EPB and moves forward.
This still works fine but not at cold start.
Issue 2: The Auto hold problem.
Sometimes, the Auto Hold despite being engaged and showing green on dashboard doesn’t hold the car in place even on flat road. The car crawls forward if i leave it in Aito Hold + D mode. This happens very less but does happen. I also make sure to press the brake fully so that Auto Hold can maintain enough brake pressure and yet the issue arises.
Issue 3: Beading near left ORVM came loose: I used a strong double tape to stick it back but quite surprised beading falling loose on a brand new car.
Issue 4: The Mahindra A.S.S.- to get above issue checked, I called the service center 13 times for appointment and in turn got one call back to book appointment. I started calling them at 10.30 in morning and was finally able to make appointment at 6 in evening.
Anyone here knows, what might be causing above EPB issue? The car should not crawl forward like this at cold start.
Also, can anyone advise on a good Mahindra service centre in Delhi?
Here’s what BHPian ashvek3141 had to say on the matter:
This is the 2nd issue I’m reading on the E-brake of the XUV700 and it is quite concerning. This definitely is a major safety concern if your ask me! So gimmicky feature not working as required is still acceptable; but such failures are non-negotiable.
Not to forget, these issues are only from the BHPians who possibly are members or know of TBHP. There might or possibly will be so many owners across who’ll be facing such issues and have no access to such a platform or don’t know about.
Here’s what BHPian NomadSK had to say on the matter:
True the car shouldn’t crawl ahead when EPB is engaged, specially when it’s almost a new car and assuming you are doing everything as mentioned in the owner’s manual. I’m ruling out mechanical issues, sensor issues, low break fluid, or worn break pads.
Technically This is how the EPB system works;
If the EPB system detects any rolling after EPB is applied, the motor on caliper re-clamps the disc to avoid any rolling.
As an added feature, to avoid roll away due the reduction in clamp force due to decrease in temperature, the EPB motor on caliper re-clamps the disc multiple times based on the temperature.
As you have mentioned, it’s happening during the cold start only (generally engine RPM is higher during this time), so more torque is produced initially during the power strokes while RPM’s are high initially, which is getting transferred to the wheels. Hence the brake calipers are not able to hold the vehicle in stationary position for this additional input of torque initially.
Since it’s an electrically/electronically – hydraulically operated system , I would first troubleshoot based on the assumption that either the voltage provided to booster break cylinder which is supposed to clamp the disc/drum, which is either providing irregular voltage, If it receives more or less voltage than necessary, this may be due to a fault in the battery and/or ECU or any software related issue. Hence check the electrical circuit/battery conditions and terminals.
Or the hydraulics of the break booster cylinder is at fault for not able to raise the pressure to clamp the disc and hold the vehicle steady. This would be the same logic for AVH too.
I would just plug-in the OBD scanner and see what error codes it throws. Probably you can visit a reputed service centre to see if any error codes pop-up before giving it to Mahindra service centre.
But but, it is strongly advised to get the critical component like brake system to be rectified/checked at service centre.
Good luck
Here’s what BHPian GoBlue had to say on the matter:
Sounds like either a software or hardware defect.
The EPB application software which is controlling the actuators is meeting all necessary pre-requisites for EPB HOLD, which is why the EPB remains engaged.
However, the CAN communication between this ECU and the TCU could be contradictory. The TCU may not be receiving consistent CAN signal from the ECU that hosts the EPB software, that EPB is engaged. It may instead be receiving a signal that says EPB is disengaged.
Thus the TCU could be getting into D mode operation (which it should not in this case, the driver command to put gear D should be overridden and prevented).
Another probability is this could be a hardware defect. There could be a feedback loop within the EPB system that measures whether the EPB is actually engaged, which could be giving a false negative during this cold start scenario. As a result, while the brakes are actually applied by the EPB actuators, the feedback from the actuator assembly to the CPU (that’s executing EPB software) could be incorrect. Thus the EPB software interprets that EPB is disengaged and sends a corresponding signal to the TCU, which then proceeds to move from P to D interpreting this as a valid operation. Please note that the TCU would also have a EPB DISENGAGED pre-requisite to allow D gear-mode operation.
As to why does the EPB not disengage on its own while the vehicle begins crawling, this could be because the EPB software application is already in EPB disengaged state (due to the scenario mentioned above).
While this is just one of the probable root causes, in order to identify the actual root cause of this issue, the first step should be to monitor/analyze CAN communication between the ECU that hosts EPB software and the TCU. This logging needs to be done while this scenario occurs, hoping it’s reproducible.
Do note that this is a safety critical issue, if the vehicle is parked on a ghat decline or on a highway shoulder, uncommanded crawling could result in fatality. Please insist on the root cause being analyzed by Mahindra, prior to accepting any warranty replacements of the EPB assembly. If this is indeed a software issue, the defect should go through the problem resolution management process at the Tier-1 supplier that manufactures this ECU (and its software), such that it doesn’t affect other owners of this vehicle.
It is also possible that this issue could be part-local, which means that there’s a variation in the EPB hardware assembly at the Tier-1 supplier’s manufacturing line where-in due to some anomaly, the behavior of the hardware is different for this specific unit, while the software itself may be functioning correctly. Other EPB hardware units are OK. In such cases, root cause analysis by the OEM is MUST, to ensure the Tier-1 goes through specific process improvements at their manufacturing line, to ensure zero part variance.
An interesting question to ask (for M&M) would be, why didn’t this get detected at EoL of the Tier-1?
Someone needs to do a fun 5-Why Analysis. And it surely cannot be the owner of this vehicle.
Keyword: Facing E-parking brake & auto-hold issues on my brand new XUV700 petrol