This problem is most common with E-Series BMWs (E60, E90, etc.). The cause of clock reset is the deactivation of the memory power supply to the radio or head unit.
Now you might be wondering why the power supply is deactivated. Well, there could be a number of reasons. Let’s take a look at how this system actually works.
Here’s what happens when your clock resets by itself:
The engine control module (DME or DDE) monitors the standby current and battery condition. When the battery capacity drops close to startability limit, the DME module will wake the vehicle and send the message to the Junction Box Electronics (JBE/Fuse Box) to reset or shut down the cutoff relay.
The Fuse Box Electronics (JBE) then regulates the bi-stable relay accordingly.
So, the main purpose of the power cutoff is to prevent the battery drain so you can start the car. But this is not a bulletproof system: if the car electronic models frequently wake up because of some fault, the wake-ups will eventually drain the battery despite this safety mechanism.
In some models (especially the E9x series) you can tell the power was reset or cutoff if the welcome lights are not working after unlocking the car.
In order to diagnose the root cause of the power cutoff, and thus the clock reset, we need to discover what is causing the power cutoff.
Before we continue, let’s put some owner operating causes out of the way:
- Lights, parking lights, blinkers left on for too long
- Ignition or ACC left on too long
- Radio left on too long
These are operational causes that can cause the power cutoff and thus the clock reset.
Now. let’s get onto the “BMW” faults:
- Weak battery/alternator fault
- Control modules don’t “go to sleep”
- Control modules being woken up
- Excessive standby current
- IBS sensor defective
- Weak Battery / Alternator Fault
If the battery is worn, the DME control unit will get the information on the weak state of the battery via the IBS (Intelligent Battery Sensor) located at the negative battery terminal. After the message comes, the DME will initiate the procedure to save the energy for the engine start.
The “alternator fault” part means that the battery is not charged enough.
- IBS Sensor Fault
Just like any digital device, if faulty, the IBS sensor can send the wrong message to the DME module (i.e. the battery is flat even though it is brand new and fully charged.) The early E6x and E9x models (up to 12/2006 production) are especially prone to this fault.
In the case of 1-Series (E8x) and 3-Series (E9x), the moisture can cause the faulty IBS to send wrong messages on the state of the battery to DME. The faulty IBS sensor can even prevent the engine from being started despite the good battery.
More common symptoms of faulty IBS are frequent wake-ups, and this brings us to the next possible cause.
- Control Modules Being Woken Up
Almost any faulty control module, sensor, or actuator can cause unnecessary (and unwanted) wake-ups. In the case of a faulty IBS sensor, the sensor itself will wake up other control modules so many times that they’ll drain the battery.
Consequently, the clock will again reset because of the power cutoff.
While the IBS is the most common cause of this problem, keep in mind that any device on the network can cause the same problem (wake up the locked vehicle).
- Control Modules Won’t Go To Sleep
This case is similar to the one above, with the exception that the control module stays awake for too long. One of the modules, sensors, actuators, or wiring problem can prevent the vehicle from going into sleep mode.
- Excessive Standby Current
While there can be many different reasons for an excessive standby current, the most common cause is aftermarket retrofitted equipment.
I’ve seen a lot of aftermarket retrofits done very badly: the power supply taken directly from the positive battery terminal or from the wrong fuse, usually from the first “live” free fuse spot in the Junction Box.
Pro Tip: Any aftermarket device power supply should be taken after the IBS sensor! When you take the power supply directly from the battery, the IBS sensor can’t monitor the current, so it will assume that the battery drains itself. The same goes when charging the battery: always use the terminals in the engine compartment.
- Battery Not Registered After Replacement
This is how the system works: The IBS monitors the state of the battery and shares the information with the DME. According to the information from the IBS, DME manages the battery charging via the alternator.
Let’s say that the old, worn battery had a capacity of 60%. You’ve replaced the battery with a new one, it doesn’t matter if the battery is genuine BMW part or aftermarket, but you didn’t register the battery replacement in the DME module.
The problem is that the parameters in DME are still set to the old battery and the alternator won’t charge the new battery, which has the 100% capacity, properly. The DME still thinks the battery has only 60% of the capacity.
I had the same problem on my BMW a few years back. The colleague replaced the battery for me (aftermarket) and I forgot to register the replacement. After three years the symptoms began to show, including clock reset, welcome lights not working, and some random faults throughout a few other modules.
You can register the replacement for either OE or aftermarket battery. The genuine BMW batteries are managed more precisely by DME, and thus they last much longer.
Troubleshooting
When I get a customer complaint about the clock being reset, the first step is to run the Energy Diagnosis with the ISTA application. There is no substitute for ISTA and no other tool can help you to diagnose the fault even close.
Later I’ll give you some tips on what to try if you don’t have access to ISTA.
The energy diagnosis is a powerful feature inside ISTA that will give you a lot of useful information:
- State of battery capacity in % (only if registered properly)
- How many unwanted wakeups and when
- Charging history (how many short drives, and so on…)
- And much more…
Energy diagnosis: Vehicle sleep mode
The following events occur in the case of a restricted waking. In the event of a fault, all of the precautions are taken to ensure the vehicle’s starting capabilities and to determine whether the fault has resulted in a flat battery.
| Index | Explanation | Index | Explanation |
| 1 | Terminal R OFF | 2 | Registration of the cause or causes in the energy history memory |
| 3 | Deactivation of terminal 30g(30 or 60 minutes after terminal R OFF) | 4 | JBE sends the power-down command 5 minutes after cutoff of terminal 30g |
| 5 | Reset of terminal 30g-f | 6 | Deactivation of terminal 30g-f |
| 7 | After terminal R is off, the vehicle does not reach an idle state. | 8 | Terminal R ON Bus communication is active. |
BSD communication line–
Glow plugs module, Oil level sensor, water pump, IBS sensor.
Troubleshooting Without ISTA
Troubleshooting electronics without the proper tools is like walking in the dark. Nevertheless, I’ll give you some tips, guides, and most common causes.
Most common causes
- Worn/old battery
- Faulty IBS sensor
- Unwanted wakeups (
Worn/old battery
You should observe how fast the starter cranks at the first-morning engine start.
Faulty IBS sensor
The first thing you want to do is unplug the IBS sensor. You can drive normally without it – the alternator will charge the battery just as in other (less sophisticated) cars. If the clock now doesn’t reset and you can start the car the next day, you know that IBS (when it was connected) has activated the cutoff relay because:
- The battery capacity drops below startability threshold
- There is excessive battery drain
- The IBS sensor itself is faulty
- The battery might be old
- The IBS might be faulty
- The BSD system might be faulty
You have eliminated:
Unwanted Wakeups
Here is the list of the sensors/modules I usually found to blame for unwanted wakeups:
- Front/rear ride height sensor
- IBS sensor (especially pre-2007 versions)
- Water ingress in the trunk (most common in E60, E61, E91, E64)
- Active steering
Conclusion
I hope that I shed some light on the “clock keeps resetting” topic. While the best way to deal with this problem is to take your BMW to a reputable shop or dealer, the diagnostic job for this kind of problem can be a real PIA. And consequently, a lot of thrown $$$ to find just one corroded wire.
So, I’ll conclude this article with a few real-world examples that I have faced in the past few years.
Case 1: 2007 BMW E60 530i
Customer complaining: Clock resets after a few hours (locked)
Cause: Aftermarket tow hitch power supply connected to battery positive terminal.
Solution: Power supply moved to rear fuse box 30g fuse.
Case 2: 2008 BMW E92 335i
Customer complaining: Clock keeps resetting overnight
Cause: Comfort Access passenger door handle keeps waking up the vehicle.
Solution: Replacing passenger door handle.
Case 3: 2009 BMW E60 525i
Customer complaining: Clock keeps resetting overnight
Cause: Battery is worn out
Solution: Replaced and registered battery
Case 4: 2008 BMW E90 M3
Customer complaining: Clock resets after a few hours (locked)
Cause: Retrofitted CIC iDrive head unit with emulator (Chinese)
Solution: The emulator was removed and the CIC head unit was activated with a patch.
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