It’s often tempting to save a few bucks by taking your car to a cheap, backstreet mechanic for service or repair, but this has often proven to be a false economy that could end up costing you a great deal more in the long run. Do you really want to trust your expensive Mercedes import to a cowboy outfit with no provable track record, just because they’re a cheaper option?

Always Choose Experienced Specialists Like Mercedes Car Service North Shore

Our mechanics have years of valuable experience working with across the full range of Mercedes models and carrying out everything from simple oil changes to complex diagnostics and full engine rebuilds.

We have invested over the years in all the Mercedes-recommended equipment and always insist on using high-quality components that will stand the test of time and ensure peak engine performance. Cheap, generic spare parts may save you money in the short-term but it’s always preferable to invest in authorised Mercedes spares, where possible, if you want to prolong the life of your car.

Diagnosing Braking System Issues with a Mercedes Benz E320

Last week, for example, we received a call from the owner of a late model Mercedes Benz E320, telling us that the brakes had failed and that he had taken the car to a local auto electrician to look into the problem. The ‘specialist’ they tried bleeding the system, but without any luck. The vehicle’s owner also informed us that a warning message ‘Brakes Defective – Visit Workshop’ had popped up on the instrument cluster. At that point, he sensibly called Mercedes Car Service North Shore for advice.

Details on the exact nature of the problem were not forthcoming during the conversation however, and all we gathered by the end of the call was that the brakes were not working properly and a repairer had tried to bleed the system but failed.

I advised the owner to get the vehicle towed to our Artarmon workshop, where we would address the issue for him, starting with one hour of diagnosis, which would involve scanning the vehicle with our Mercedes SDS (Star Diagnosis System). Next, we would need to make sure the brake lines were attached correctly so we could do a wheel alignment.

Our Expert Knowledge of the Mercedes E320 Model Aroused Suspicions

Alarm bells had gone off in my head through this entire conversation, as these cars have SBC (Sensatronic Braking Control) systems, which generate apperoximately 100 bar (just under 1,500 psi) of pressure. Without the previous mechanic having proper equipment and specialist Mercedes E320 knowledge, my instant fear was that a lot of things could’ve gone wrong during the previous service and made matters worse. We suspected the owner could have saved himself hundreds, if not thousands of dollars, had he appointed the right person to do the right job with the right tools in the first place.

Fortunately, all roads on the internet lead to Rome. And – to run with the metaphor – when it comes to repairing luxury European imports, Mercedes Car Service North Shore is Caesar!  Which is another way of saying that there isn’t a Mercedes problem we can’t fix.

 Interpreting the Issues Behind the Mercedes E320’s Warning Lights

The Mercedes E320 arrived at our workshop on a tow-truck as scheduled. We immediately noticed the brake pedal was very hard, then became spongy. Warning light messages showed:

– SRS (Supplemental Restraint System) warning light on instrument cluster.

– Service E is overdue.

– Brakes defective

– ESP (Electronic Stability Programme) defective

We could hear the SBC (Sensatronic Braking Control) system pumping but it sounded very weak, as if there was no fluid in the system. There was also blue brake fluid all over the SBC unit, which was a bit of a concern.

What’s more, the tow-truck driver complained the transmission would not move out of ‘park’, so he had to remove the gear-stick surround and activate the manual release to get into drive or reverse gear and load it on the tow-truck.

With all the information to hand, the first part of the diagnostics was to scan the electronic system with the authorised Mercedes SDS (Star Diagnosis System).

The main complaint was that the brakes were faulty, and that there was a lot of under voltage faults and hydraulic faults found within the SBC system. Consumer shut-off was at stage 2 – a bad sign. The main battery also needed to be replaced before any further diagnostics could be done.

After the initial 1 session of scan and data reading we contacted the owner of the Mercedes and advised him on what we had done so far and that another two hours and a replacement of the battery were required before we could proceed, at which point we got the go ahead to continue.

 Further Diagnostics Required on the Braking System

We replaced the main battery with a Duracell battery, cleared faults and re-scanned the system. Much of the under-voltage faults disappeared (but there were many other faults), however we were only asked to look into the braking system not the other issues.

The faults in the SBC were hydraulic solenoid faults and a pressure reservoir fault.

Some useful facts for you regarding SBC (Sensatronic Braking Control) systems:

– The SBC system has a life of around 300,000 depresses of the brake pedal, and when this is reached the unit must be replaced.

– When the brake pedal is depressed, the SBC system gets an input, together with other data, like steering-angle, yaw-rate, wheel-speed, etc. At which point the SBC decides which wheels to activate the brakes on and how much pressure to apply.

– Opening the driver’s door will pressurise the brakes. If the SBC system is not deactivated before repairs, just by opening the driver’s door will send 50 bar of pressure to the brake lines (1 bar of pressure = 14.5 psi) Just imagine 50 bar of pressure exploding at the mechanic working on the car. It could be catastrophic and even life-threatening.

We checked the system to see the operating time of component A7/3 SBC unit. But the scan tool flagged ‘Service Threshold Reached’. We did not get the fault C249F. The operating time of the SBC hydraulic unit had been exceeded (brake pedal count had reached 300,000 depresses) and we were only getting hydraulic solenoid faults and pressure reservoir faults. In addition to these findings, there was also incorrect brake fluid in the system.

Bleeding the Mercedes Car’s Faulty Brakes

We carried out a manual bleeding procedure to the SBC system. We also carried out electronic bleed procedure with Mercedes SDS (Star Diagnosis System). In total about two hours’ labour and 4 litres of ATE SL6 Brake fluid were required to try to bleed the system and to get rid of the incorrect brake fluid. It transpired that the electronic bleed procedure had failed.

We also found a fault, while bleeding the brake system, that informed us that the solenoid was only receiving 6.1V. That did not make sense, because there was a brand new battery in the car plus we had a Fronius power supply, offering 13.5v at min 20amps to the entire car.

Next, we looked up the wiring diagram, as the front SAM (Signal Acquisition Module) supplies power to the SBC. We checked that the terminal in there was 13.5v. We also checked ground terminal to body and noted that there was no voltage drop (the SBC supplies voltage to the ESP internally). 

Interpreting the Mercedes E320’s Diagnostic Results

  1. The official service threshold has been reached.
  2. The system would not build up pressure (pressure reservoir fault).
  3. There were hydraulic faults in the braking system and it would not bleed.
  4. SBC only supplying 6v to ESP solenoids.

Keeping the Mercedes Owner Informed During the Diagnostics Procedure

We called the owner, advising him that our diagnosis led to the conclusion that the SBC unit needed replacing.

The customer then advised us that the electrician he originally asked to fix the problem tried to bleed the brakes but could not, so he hired a “mobile Mercedes guy to fix it”.

The second mechanic put in a second-hand SBC unit and tried to bleed the system but failed. The left front brakes also couldn’t be bled properly.  It was at this point that the car was towed to Mercedes Car Service North Shore.

During our investigations of the E320, we also noticed that the steering rack was replaced due to oil leaks, but noted that the brakes had failed before that.

So, to recap: the owner (at this point) firmly believed a ‘new’ SBC unit had been installed (even though the one installed had already reached 300,000 depressions!). He was justifiably angry when we told him that the unit wasn’t new after all, but actually second hand! All of which meant that the customer had (prior to bringing the car to us) now paid two so-called mechanics to fix his Mercedes (three counting us) and was no closer to having the car back on the road.

We asked if there was anything else we needed to know about the previous repairs on the car, before proceeding, and advised the customer that we could not trust the other mechanics’ diagnostics and repairs, and that we need to carry out our own analytical diagnostics.  The owner understood and gave us the go-ahead to fix the problems. 

Swiftly Correcting the Faulty SBC Hydraulic Unit

These are the repairs that we performed on the Mercedes E320:

  1. We replaced the SBC hydraulic unit.
  2. We ran initial start-up procedures.
  3. We performed the manual bleed procedure.
  4. We carried out the electronic bleed procedure.

After the replacement of the SBC unit, the bleed procedure went off without a hitch. The pressure reservoir passed the test and nd the pressures in each wheel were at 56 bar and even.

The Importance of Always Road-Testing Vehicle Repairs

At this point, it was time to road test the car’s brakes. Fortunately, it was raining on the testing day. The ABS (Anti-Skid Braking System) and ESP (Electronic Stability Programme) tests, when performed on wet roads, are much more revealing. Happily, all systems tested were working correctly.

However, at this point that we noted that a new fault had appeared on the ESP (Electronic Stability Program). It was a fault for the ‘left front-wheel speed sensor implausible signal’ (yes, that’s actually a thing!). The ESP pressurises the wheel so if it’s losing traction, the car doesn’t spin out of control. So, it is a fault that must be fixed, as a matter of priority.

Further Issues Detected with the Steering-Wheel Alignment of the Mercedes

While driving the car, we also noticed that the steering-wheel alignment was significantly off to the right, pointing to 1 o’clock rather than 12. While testing the ESP, left rear-wheel spins on take-off and the system would lock up the left front-wheel and log a fault with the ‘left front-wheel speed sensor implausible signal’. All of which meant we had yet another fault to iron out!

The SBC system was now fine, but the ESP presented a new problem, an issue we couldn’t identify earlier because the brakes were not working at all, hence we couldn’t road- test the car.

But, further problems equal more expense for the owner, so we contacted him, explained our findings and said we needed more time to carry out diagnostics of the ESP system fault (approx. 1-2 hours in total). He begrudgingly gave us the go-ahead!

Discovering the Mercedes Benz E320’s Tie Rod is Bent

Back in the workshop we hoisted the Mercedes, to swap wheel sensors from left to right, road-tested it again and revealed the same fault came back on the left-front. We also read the live data and the wheel-speed appeared to be okay.

We then examined the wiring diagram. The wheel-speed sensor wiring runs from the sensor to the ESP unit, via a single connector, which was functional. We then connected an oscilloscope to read live voltages to the sensor and ESP unit, which were spot-on. By this point we deduced that the ESP (Electronic Stability Programme) was logging a fault, because the steering-wheel was off-centre, so it falsely believes the wheel to be spinning.

Armed with this knowledge, we carried out a wheel alignment and found that the left-front tie rod was bent! We needed to rectify this before further testing could be done. Then we remember that the owner had said that he had the steering rack replaced, due to oil leaks, and the tie rod is part of the steering rack.

Occam’s razor being our friend in such situations, we rang the owner to ask if he had been involved in any accidents due to the braking system being faulty? He replied that he hadn’t, and that the car had not been driven since the brakes failed (at which point it was taken to the first mechanic). The steering-rack was replaced at that juncture but the repairer could not fix the brakes, so just replaced the steering-rack.

We then discover that the steering rack (which had a bent tie rod) was also a second-hand unit from the recycler! You see why it always pays to take your European luxury automobile to a fully qualified mechanic in the first place! With Mercedes Car Service North Shore, you are guaranteed quality, brand name, brand new parts installed and diagnostics performed with the correct software and machinery.

 Further Mercedes Benz E320 Repairs Required

 So, with more dodgy dealings discovered, we needed yet another hour’s labour to replace the left tie rod and carry out wheel alignment, before any further diagnostics could be attempted.

This done, we replaced the left-side tie rod, carried out the wheel alignment and steering angle adaptation, then performed another road test. However, the same fault with the ESP was displayed.

What Our Expert Mercedes Diagnostics Had Revealed Thus Far

– The SBC is fixed.

– The ESP is part of the SBC unit.

– The wheel-speed sensor has been swapped and the left side is faulty.

– The signal coming out of the wheel-speed sensor is correct at the ESP unit.

– The SBC unit was covered in blue brake fluid when the car came in.

– The second technician changed the SBC unit with a second-hand one.

– After the second-hand unit was fitted the left-front wheel would not bleed.

– The left front wheel locks up when the left rear wheel keeps spinning, then logs a fault.

Finally Getting to the Root of the Problem

So, could it be that the lines were fitted incorrectly? With multiple lines running through a system, it’s always best practice to mark which goes where and ideally take photos, so you can refer to them if needed.

When we replaced the SBC unit, all the lines were marked and fitted exactly, but that doesn’t help if they were incorrectly set up by a previous ‘mechanic’ and were wrong to begin with! Given the questionable practices of the two previous so-called-mechanics, we feared the worst. So, we conducted a thorough search through our Mercedes WIS (Workshop Information System) for more information. WIS has factory diagrams and correct factory ‘lines map’. And voila! We discover the left-front and rear lines had been swapped!

This could be a major safety issue if the ESP system, sensing a left-rear wheel spin, applies the left-rear brakes at the wrong time, causing the front-left brakes to lock. In addition to which, if the ESP thinks this is going on, it logs a fault for ‘left-front sensor implausible signal’.

So, armed with this important information, we re-routed the lines, did another road-test and, finally, all was well!

Drawing Conclusions from the Experience

The moral of this story being that the owner of this car could have saved themselves many hundreds of dollars if he had brought his Mercedes E320 to Mercedes Car Service North Shore in the first place. Because, as with all things in life, you get what you pay for. And with so much at stake, it always pays to take your car to a fully qualified Mercedes specialist whenever a problem arises.

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