My ML 320 (2000) is going crazy with the BAS/ESP light: On the front panel this light is coming on and off in a random way, noting that:

- WhentheBAS/ESPlight is on, the ESP is still working and flashing in the panel (I tried it on slippery roads) but youcan't turn it off manually,the yellow triangle will not appear in the panel.
- When theBAS/ESPlight is off, all is working and you can turn manually the ESP off.

When scanned with the 'Star' scanner, it is giving the following faults:

- Instrument cluster fault: CAN communication with the bas control unit.
- Test control module N47-5 (ESP/BAS) control module.

Please help me asI have changed the break light switch and still the BAS/ESP light is coming 50% of the time on in a very randomized way!
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Hi,
I'll reply with what I can.

Firstly thepanel lights are working as they should if indeed something is wrong with the BAS/ESP.
However you haven't mentioned ABS.

The light in the ESP switch shows that the system is INOPERATIVE rather than working.
The Yellow Triangle ON shows that the system is actually MODULATING WHEEL SLIP. i.e. WORKING rather than just ON / OK.

So what could be causing this.

OK you have had the system scanned but the codes do not help (me) much. They show a CAN (digital highway / network) fault and that the ECU is suspect. Diud they infact test the module N47-5? Unless something dire has happened i.e. Car got flooded etc.
You do not give much history regarding the fault. i.e. When it started, what other symptoms have shown up, weather at time, frequency/ duration of fault etc. All helps with this sort of problem.

I would start by ENSURING that battery violtage is OK. What is the battery voltage with engine off. 13v? During starting. 13v? With engine warm at idle. 14v? Engine at lets say 2000 rpm? 14.5v?
ESP and similar systems are voltage sensitive. Low voltage during start can cause these systems to shut down till next start.

Next I would check the wheel speed sensors for dirt (on sensor tip / will need to be removed) and good connectivity to the vehicle wire harness. Careful visual inspection.

You say you have CHANGED the brake light switch. Sure this was fitted / adjusted correctly or was it just inspected and replaced. The switch has two circuits NO / NCand often exhibit erratic connectivity within the switch at least on one circuit. The fact that the brake lights come on does not signal that the switch is OK?


Sure your tyres are OE spec/ size and in reasonable condition for wear?

If all of the above prove OK then it gets a LOT more difficult / expensive.
Basically you have to determine where a CAN fault could be occuring.
This is not a DIY type activity since there is no simple guide as to what to do.
Modules attached to the CAN has to be isolated and every connection checked for corrosion, water ingress etc to see where/ how a short (especially an intermittent one) is potentially occurring.

With the codes you have got a dealer would most probably change the ECU (watch your pocket book).
This MAY resolve the problem although I would place a bet that it won't.
If it doesn't then the dealer would most probably continue changing other parts till the problem is located and issue you with a big bill for parts that may, or may not, need changing.
Changing an ECU is often though to be the solution to a problem when in reality the fault was a poor connection to the ECU.
Removing / refitting another ECU may just happen to cure the problem by improving the connection. Likewise bent pins, backed out pins in connectors etc.

ECU;'s are very expensive to replace (although low cost to make!). Reliability is extremely high.
However they do not like water / moisture. Issue is nearly always with inputs or the CAN linking the parts of the system together.

If they didn't test the ECU why not? What were the results?

Good luck.

Stuart

Let us know how you get on with the initial checks.

 

First of all I would like to thank you for this very detailed answer, I really appreciate it a lot especially that I am in deep need for help.

Regarding the ABS, the system is working perfectly with no symptoms.

I think that I wasn't clear in the ESP part: what I meant is that when the BAS/ESP light is on in the panel, I can't switch off the ESP anymore but this ESP light will be flashing (modulating the wheels) in slippery conditions meaning that it is working. The only thing abnormal is that when I try to switch it off manually, the yellow triangle should come on and remain in the panel and this is not happening when the BAS/ESP is on. But when this BAS/ESP light is off, everything is normal.

Regarding the break switch, there was no fault in the scanner related to it, we tried to disconnect it and scan the car a second time, and the fault appeared. Finally we placed it correctly again and during the third scan no fault related to the break switch was there.

Regarding the wheels, I don't think there is a problem because, when I first bought the car with the same tires, the BAS/ESP light was not showing for the first 3 or 4 months.

I would say in relation to the frequency in which this light is coming on that always in the morning it is off (even if I turn on and off the car 5/6 times) usually it comes on during ignition only and most frequently around noon and after noon, when on it will remain until the next day and would disappear as I said above in the morning time.

Regarding the battery, I would say that we didn't check it with that attention and thanks for highlighting this point (would be grateful if you could give more details in relation with this subject). Will check it and come back to you.

If everything is ok with the battery (I hope not) what would be the next step to do? As you said in your reply, the dealer is insisting on changing the ECU (700 US$) is there any way to test the ECU and make sure that it is not damaged?

Many many thanks for your help...
George

 

OK,
These warning lights are so confusing.
I'm not an ML owner so assumed there was a light in the switch. Maybe this wasn't correct.
Fundamentally it doesn't make any difference whether the light is in the switch or elsewhere.
The important bit is that there are two ESP lights.
A malfunction (warning) light and a system operating (modulating / intermittent) light. On MB's this modulating light is usually in the form of a Triangle.
In addition the triangle is often illuminated (continuous) to show that the system has been turned OFF manually. = Take Care.

I will continue on the premise that the system is no longer working as it used to and that the tyres etc were fitted before the fault occurred.

As I stated previously it is important to ensure battery voltage is within spec.
All you need is a voltmeter at the battery terminals.
Since microprocessor output cannot be predicted if operating below specific voltage many systems like ABS shut down if voltage drops outside a threshold.
Many people think that vehicle electrics are 12v. In reality they are more like 14v!
Once voltage goes below 12.5v the battery is damaged beyond "repair".

Now if the dealer wants to change the ECU I see no reason for stopping them doing so long as there is an understanding that you do not pay if it doesn't resolve the problem!

Finally Star identified that N47-5 needed to be tested. So what were the results?
If indeed this test was done and it confirms the ECU needs replacing the ECU should resolve the problem.

Personally I would unplug the ECU, examine its connections very carefully and reconnect to see if this resolved the problem before actually changing the ECU.

The CAN fault suggest an Open or Shorted connector somewhere.

 

What's making me hesitant to change the ECU is that itis not always malfunctioning meaning that the ECU is not damaged?!

I am more convinced with your opinion: Batery or connection problems, will investigate on this tomorrow.

 

Yep.
So what are the battery voltages?

Finding a CAN fault is not a DIY type job. It requires a systematic process of elimination and extremely careful observation.

Star diagnostics is actually designed to take a technician thru a series of tests by means of a series of screen prompts so that a relatively untrained individual can determine the cause of a complex problem BUT AT A COST TO THE OWNER since only MB have such a diagnostics procedure.

If this series of tests does actually point to the ECU then I have to agree that the chances of the ECU being at fault have increased BUT I CONSIDER THAT THE RESULTS ARE NOT 100% CONCLUSIVE.

The alternative is a highly experienced individual with an understanding of all systems from first principles. However this can be a very time consuming job.

Any other clues to help. Something else that doesn't work. Collision damage, car went for a service and problem has been since etc.


So back to the beginning.

Voltages?When was the battery last changed.
The fact the battery actually manages to start the car does not give it a clean bill of health. Voltages can drop below a threshold as the max crank load is applied which is why I ask for cranking voltage to be measured. Modern highly geared starters are much kinder to a battery than the old fashioned high current devices and battery failure is not quite so clear cut.